Logitech Squeezebox Boom VFD Display Repair Guide Part 2: Filament Power Supply

Please refer to Part 1 for instructions on VFD common information, Boom disassembly procedures etc.!

Fixing the "Filament Starvation" Phenomenon on the Logitech Squeezebox Boom

This entry is about a problem that apparently exists mostly in Boom units. I never found it in Classics or Transporters.
So what is filament starvation anyway? I got this term from the Noritake technicians - Noritake Itron is the manufacturer of the beloved VFD displays in the older Squeezebox devices such as SLIMP, Classic, Boom, and Transporter. It means that the heater wires which you can see horizontally across the display in the frontmost position are supplied with insufficient power so the display cannot show its full brightness. Even worse, the display may show shadowy sections especially at the left and right side. No matter if you just replaced the old VFD by a brand new one, you may be greeted with a sight that looks pretty rotten.
Here is an example I took of a unit in factory button test mode. Observe the inconsistent brightness of the blocks across the display:

Or even worse: this is a brand-new display on brightness level 2 / 5 (lower brightness makes the problem much more apparent):

The same display can also look like this (same brightness level):

So how is this issue identified vs. a generally-aged display?

Idenfying the Actual Boom Display Issue

When a display begins to look shoddy, there are multiple (mostly concurrent!) indications for the respective problem behind the symptoms:

• display shows 'shadowy' sections rather in its center --> probably burnt-in pixels --> display replacement advised. This can go as far as recognizable digits from the clock screensaver which appear as a permanent dark cast across the actual display content, of course mostly in the places where the clock would have shown its digits
• display gets darker beginning at the left or right side. The center is the brightest part until it fades away completely --> power supply failure
• display is completely dark, or quickly fades from barely readable to completely dark shortly after powerup (after being separated from the power supply) --> power supply failure. This recovers when the Boom has been sitting around without power applied for some hours, but quickly comes back after powering up again

Most Booms have both simultaneously, i.e. burnt-in pixels as well as a failing power supply. When you replace the display anyway, it's worth while applying the power supply fix described here. That is, if you find that the display replacement alone did not end in the expected bright and shiny new look.

Edit 2020-06-08: there is a new blog post about this matter specifically, to be found here: https://joes-tech-blog.blogspot.com/2020/06/vacuum-fluorescent-displays-how-they.html

About VFDs

Wikipedia.com gives you extensive information about how a VFD works. Please take a look to understand the basic principles of operation.
The Noritake displays employed in Squeezebox devices need mainly four supply voltages:

a) +5V operating voltage at low current for the embedded controller chip
b) +55V grid voltage
c) +5V filament voltage #1 (left side)
d) variable voltage between +1.5 and +3.0V for filament voltage #2 (right side)

A high current flows between c) and d), I estimate it about 800mA.

EDIT 2023-01-19: well, after all these years, I have finally come to measure it and actually it is far less. It's a unit where the the diode fix is already in place. With that in the loop, the amperage is around 105mA constantly. It's a little bit more when the display brightness is higher, and is zero when the display is off.

What we are going to fix here is d). A little theory for those who did not visit the Wiki article above. A VFD is very similar to a classic vacuum tube in that it has a heated cathode that emits electrons, a grid that controls electron flow towards the anodes, and eventually anodes to "pick up" the electrons which in a VFD are the individual pixels. If a pixel is positively charged, it attracts the electrons emitted and the phosphor coating causes the pixel to glow.
While the heater wires are supposed to permanently emit electrons, the grid sections between the heater wires and the pixels control which group of pixels receives electrons at all by setting all grids that should be blocked to the a positive potential so they basically catch all free electrons. Only the grid section where electrons should pass through is switched to a neutral potential so the electrons can get past it. The neutral part in the grid sections is scanning to enable all groups of pixels in a cycle. This happens hundreds of times per second so the human eye will not notice it. A slight flicker can be observed when the eye moves quickly across a VFD though.
Filament starvation causes the heater wires to reduce or even stop electron emission. There can be any degree between hardly noticeable to completely dead. In some cases, both heater wire connections are fed with +5V which means there is no voltage drop at all. While the display may be fully operational, it will act like it's dead.
So the thermic electron emission in a directly-heated cathode (such as the heater wires in the VFD) is caused by a voltage drop across the heater wires. The higher the voltage drop, the more the heater wires will glow and thereby emit electrons. In reverse, if the voltage drop gets too low, the electron emission will slow down or stop. A considerable current is needed to heat the wires up. In dark environments, you will even see the six horizontal wires glow. This is also a reasonable limit for the driving circuit. A balance should be found between sufficient electron emission that is just enough to have a good visual impression that is not disturbed by the heater wires glowing. The corridor between both is rather narrow.

Boom Failure Mode

While I never had any Boom with failures regarding the filament voltage #1 which is a stable +5 Volts whenever the Boom is connected to the external power supply (yes, even in the deepest standby mode), the other side of the filament is apparently the output of a power supply circuitry that has some still-unknown component that fails over time. It is meant to supply variable voltages depending on the selected brightness level, so there is a more complex circuitry behind that that is designed to handle the high current... or rather not apparently.
If you have a multimeter at hand, you will be able to measure +5V at any of the three leftmost pins of the display - positive test lead going to the display, negative test lead put to GND which can be found at any of the screws that hold the board in place while mounted. If not mounted, use the gold-plated screwholes instead. You should also measure approximately this between GND and one of the three pins on the right side:

Level 5: 1.418 Volts
Level 4: 1.414 Volts
Level 3: 1.413 Volts
Level 2: 2.513 Volts
Level 1: 2.511 Volts
Level 0 (off): circuit open

By the way, if you switch the display 'off', both filament voltages might be GND or dropping towards GND. There seem to be releases of the Boom where the display is actually turned off, in contrast to what I assumed. Just found this out. Interesting. I will probably investigate deeper here because that is what I would like to see in all Squeezebox devices when their displays are not showing anything. Just imagine how much power might be saved, and most Booms are pretty wasteful in this respect by keeping the heater wires hot all the time, no matter the operation mode.

So levels 5 and 4 mean a voltage drop of about 3.6 Volts which I think is pretty extreme. The voltage drop in levels 3 thru 1 is about 2.5 Volts.
When a Boom begins to show filament starvation, what happens is that the variable filament voltage rises too high. I measured up to 5.5 Volts in defective units which means the right side is even supplied with more volts than the left side, reversing the electron flow, but the resulting 0.5V voltage drop is not getting you anywhere.
So the failure mode regarding the right-side power supply is not that it fails and is eventually 'open' or falling to the potential of GND, but is reaching or even exceeding +5 Volts instead. So what fails is apparently some kind of pull-down circuit that is designed to provide stable voltages below 5V at a higher current.
We have +5V on the display's left side so the right side needs at least 1V more or less for a voltage drop big enough to start the magic, or better 2 Volts. The higher the voltage drop, the more the heaters will glow, so there is a voltage drop where undesired effects begin to show. Heater wires glowing red is probably not what you want. They can withstand a *lot* of power, so they will probably not take damage, but will emit a ton more electrons than actually needed. This will make the active pixels shine brighter which will more quickly consume them. Consequentially this will cause shadows in the display caused by pixels which burnt down quicker than others. Which puts you back to square one, having to replace the display again.
So let's assume that we want to define and limit the voltage drop. Otherwise, you could set the right side of the filament to GND, creating an effective voltage drop of 5V, and you'd be done. But that would be too easy, wouldn't it? A display might last some weeks or even months under this condition but it would cook itself to death.
Unfortunately, to this day, there is no technical documentation available from Logitech, and it is uncertain if it will ever surface. The majority of the Boom consists of tiny SMD parts which are hard to figure out, mounted to a multilayer board (at least 4-6 layers, I think). It's practically impossible to know what part of the circuitry is failing, and what could be replaced to fix it.
Basically, even if we knew, the design has an apparent flaw. A brand-new component will just solve the issue for a time before it starts failing all over again.

The (Pseudo-)Solution

IMPORTANT: You should not apply this fix unless you are more or less convinced that your Boom is suffering from the filament starvation phenomenon! Because there is no way of knowing if an intact power supply circuit could be damaged by the fix so things get even worse.

I have a more 'brutal' approach to this. Assuming that the right-side power supply has failed and generates +5 Volts or more continuously, why not pull it down to a more reasonable level with the help of just a few additional parts? While this will eliminate the ability to create arbitrary voltages, I found that a constant voltage drop will still allow you to fully control brightness levels. And it's really a very simple addition:

What you see here is the right side of the display. The three pins at the top are linked together (a tribute to the higher current that passes them). This is by design. Even if the three pins are not connected to anything, they share the same potential. My idea is to use three simple diodes in series from these pins towards GND, shown in yellow.
The diodes used can be run-of-the-mill 1N400x-type diodes which are available for just a few cents each. Just be careful to order ones which are capable of handling up to 1A of current. Typical diodes have a voltage drop of around 0.7 Volts each, so a chain of three creates a voltage drop of ~2.1 Volts. Assuming that the original voltage is around 5 Volts, the diodes would pull it down to about 2.9 Volts.
That is in the range of the voltage that an intact circuitry would generate; a voltage drop of 2.1 Volts is enough to give you a nice clear display in all situations, and even though this is less than the up to 3.6V voltage drop in the original circuit, giving the display a lower voltage drop is likely contributing to a longer display life. Visually it's negligible.

Current flows in the direction of the arrow towards the 'bar' in the schematic, and the bar is what you can also find on one end of the diode. That is the cathode (or minus) end, whereas the other end of it is the anode (or plus).
The nice thing about the diodes is that they cause a voltage drop but do not convert this drop into a lot of heat like a power resistor would. Furthermore, the current direction is still forced to be in sync with the original design.
This has proven to be a cheap and reliable solution in many cases (up to 60 at this point). Whenever I do a display replacement, many times I'll include this fix because the power supply decay becomes visible. Newer displays at low brightness are particularly good at helping to discover this.

Tools Needed

What you need for this repair is:

• all the tools for disassembly / reassembly (see Part 1)
  
• soldering iron with fine tip (~ 285°C, no more than 40W)
• 3 1N4001 (or 1N4002, 1N4003, whatever) silicon diodes with 1A rating
• 1 pair of pliers
• 1 small piece of heat shrink tube ~6mm diameter
• 1 small piece of heat shrink tube ~2mm diameter
• highly recommended: a "3rd / 4th" hand tool to hold the diodes in place for soldering

Creating Your Own Fix

So here is a guide on how to integrate these diodes. Please consider reading it through the end first before you start your own repair. There are some tips hidden here that could appear out of sequence.
From your collection of diodes, select three:

Keep in mind that we want a chain where one end of the overall construct is the anode and the other is the cathode. All diodes between need to be in line, the anode of one connecting to the cathode of the next. Reversing any diode in this chain will probably end in something nonfunctional that acts like an open link.

Pick two, bend the anode (unmarked) wire of one 90° to the side. Do the same with the cathode (marked) wire of the other.

Now let's join these two with a little drop of solder. First cross the bent pins, put the diodes as close together as possible, and solder:

The result is a 'Pi' pair of diodes:

Now bend one of the pins away 90° again. The third diode will be soldered to this wire. In this case, we bend the anode wire of one diode:

Also bend the cathode side of the third diode that comes in now:

Life gets easier if you clip the wires of the diode contacts that we already soldered together:

Now cross the two bent leads again and solder them together. Ensure that the anode of one diode is connected to the cathode of the next diode, or vice cersa. This needs to be consistent, otherwise the fix will not work.

Finished:

The end result is a series of three diodes in the smallest possible form factor:

The brave of heart could try a little dry test now. If you power up the Boom board, holding the diode cascade's anode to one of the three rightmost display pins and the other lead to the gold plated screw hole next to them (see schematic in "The Solution" section above), this should immediately light up the display to a much brighter level if it works. But make sure you do not touch anything else on the board with any side of the diode cascade! If nothing happens, or it gets blindingly bright and you see the heater wires getting red-hot, there is something wrong. Please stop immediately, recheck, and do not continue because this is not recovering by itself. In doubt, better send me a message and I will try to help you.

We need to isolate the diodes a little to ensure that we won't create any short circuit in the precious Boom board. I recommend heat shrink tube, one piece of ~6mm diameter (yellow in the following images) to cover the barrel of diodes, and another of ~2mm diameter (blue in the photos) which we will see shortly.

Prepare two pieces like so:

Mark one piece of the 6mm heat shrink tube so we know where the cathode of the chain is. It should correspond with a cathode marking on the last diode of the chain (it's the one closest to the camera in the following picture):

Push the 6mm heat shrink tube over the diodes, and the 2mm one over the cathode lead:

Then apply heat (150-200°C):

The anode wire (the unmarked side) will go across the three pins to the right of the display. As there is not enough space on the main board's front side, we will place this piece in the back.
First, bend the anode wire 90 degrees off:

 
Place it across the three pins as shown here and solder:

Please make sure the lead you attached to the display's pins does not touch the Wi-Fi antenna metal pad! Missing this point may damage your Wi-Fi board, or worse. The antenna pad has some degree of GND level. If both pieces make contact, you have around 5V voltage drop, so its way too high, and goes through the Wi-Fi card, too, which can't be good. Please avoid from the start. Place the lead as far right as possible. In doubt, put some isolation tape in between, like Logitech did in the original design (this strip of black plastic adhesive tape is missing in the photos). The diode contact should still touch all three solder pads of the display but this is not vital. It also works if you solder the diodes to just one of these pins as they are shorted together in multiple places on the board as well as in the display itself.

Clip the excess wire and bend the diodes so the cathode wire points to the right:

You can see in the previous picture that there is not much clearance between the diodes and the antenna. The gap should be as big as possible. Or, if you are even smarter, you first read up to here and remember to put another small piece of 2mm shrink wrap to this end of the diode cascade to isolate this properly :o)
I helped myself by bending the entire diode setup after soldering which becomes apparent in the next pictures but it's certainly not the nicest solution.

You may have to adjust the length of the 2mm shrink wrap tube. The wire needs to be soldered to the screw hole. Bend the lead to go there the shortest way. Prepare the diode's lead as well as the outmost section of the screw hole gold plating with a bit of solder:

Now join both:

Make sure the contact is stable because there will be some (mechanical) load on it once you reassemble the Boom.
You should not see any indication of the fix on the front side:

But on the back - see top left corner!

That's it folks! You're done!

I'd be overjoyed if you share your results and thoughts in the comments. Thanks for reading and for your feedback!

Final Words

Some legal stuff because you never know: please bear in mind that I am writing this as a hobbyist, not a professional. I describe personal ideas here which is only one of many ways such a repair can be achieved. I cannot guarantee that following this guide will lead to a good result, and cannot be held liable for any personal, physical, or monetary damage anybody suffers by following this guide.
I am open to advice if anything described here is wrong or can be done better. Please let me know in the comments if you find there is anything left to be desired.
Thank you!

Logitech Squeezebox Boom VFD Display Repair Guide

Tired of seeing this?

No question, the Squeezebox Boom is a fabulous device. However, some small mistakes in the design as well as in the documentation make it susceptible to some annoying symptoms of aging, becoming apparent by a shadowy / fading display, or the display showing nothing at all any longer.

What happened? 

To make it short: we have a mix of aging of the display itself, plus aging of the power supply circuitry. Both lead to faded or completely dark displays.

Edit 2020-06-08: more details on this can be found in this new blog post: https://joes-tech-blog.blogspot.com/2020/06/vacuum-fluorescent-displays-how-they.html

The Squeezebox Boom, like many other devices of the Squeezebox series such as Transporter and Classic, employs a Vacuum-Fluorescent Display (VFD) for user interaction and entertainment. Look here for more info: Wikipedia.com

Why VFDs?

VFDs are kind of old-school today. Most people know them from (older) table calculators, cash registers, video recorders, dash displays in cars, etc. Their main advantages are that they are pretty bright and fast. There is hardly any "lag" when a pixel is switched on or off. They are much better in this respect than LCD displays. They emit a bright cyan/green light which can be easily modified with filters to grey, green, orange or whatever.

I think Logitech chose VFDs because they simply look good in operation. As the Squeezebox UI uses a lot of animations and visualizations, VFDs are the displays of choice for this kind of application.
Logitech picked the Noritake MN16032 glass module and implemented the driver themselves. So what you need is a MN16032, not one of the GU160x32 modules that Noritake is selling as well. The GU series is basically the glass module mounted on a PCB with some microcontroller and power supply. The Boom contains all of this.

Edit from 2017-06-19: Noritake Itron is updating the MN16032 to a new revision. The previous one is the MN16032G, the new one is named MN16032GB. You can purchase any, both will do.

One main disadvantage of VFDs is that they are aging, just like old cathode-ray tubes (CRTs known from TVs), or plasma displays. The phosphor coating of a pixel burns up over time while it is on. The speed of decay is determined by the time the pixes is on, and its brightness. The longer and brighter a pixel shines, the faster it will fade. So aging is no issue when the display is completely blank.
The outcome of permanent content creates ugly artifacts such as these, from a display that actually shows "all pixels on":

Some static text has been in the same place for a very long time. It has burnt in so much you can read the shadow of something like "RDSI: 19,392Mbps" in the third line. The text in the bottom line seems to have varied but not really much as there are clear shadows of M, H, D and T characters.

How does Logitech make it worse? Screensaver!

This process cannot be stopped except by not using the display at all. But things can be improved by limiting the maximum brightness of the display, and not using what Logitech prefers to call "screensavers". Because these actually do the exact opposite. A permanent display of the clock time or the current weather will lead to partial fading of your display. That's not what I would dare call a screensaver.
Moreover, the clock time is displayed in the same place all the time. It does not "wander around" on the display to make use of many different pixels and use them up equally. As a result, most Boom displays fade in the center first. The photos above show how bad this can get. It is clear to see that the shadows four large digits exist where the clock time usually appears.
Generally I accuse them of not mentioning the risk of VFD aging anywhere in their documentation. It's a shame but the people responsible for the documentation probably weren't aware of the problem at all.

Automatic Brightness and Why I Don't Like it

Besides destructive screensavers, Logitech screwed up the automatic brightness behavior. While it is possible to set a minimum brightness and a sensitivity, it is not possible to specify a maximum brightness. And in my opinion, the sensitivity is a bit too far on the high side even on its lowest setting, i.e. the display is at the highest brightness most of the time.
Imagine you have a Squeezebox Boom on your bedside to act as an alarm clock. Sure you want to see the clock time at night, but what about daytime when you are at work? Daylight will cause the automatic brightness control to drive the display at its maximum capability, without anyone even looking at it. I think that is how most displays suffered from premature aging, while nobody cared.
So my recommendations to increase the life expectancy of your displays are:

• don't use automatic brightness. Set a fixed brightness as low as possible
• never exceed brightness level 3 (out of 5)
• in standby, do not have the display show a clock time or anything else that resides in a static position on the display

Many people will now think that these measures render their Boom useless. Well, this is just if you care more for the display life than for your personal comfort. There is still a chance to replace burnt-out displays. That's what this guide is all about.

VFD Filament Power Supply Design Issue

Unfortunately, there is also a design flaw in the Boom concerning the filament power supply. The filament wires are directly behind the front glass. In dark environments, you can see them in the form of six horizontal glowing lines. The Boom VFD has a filament voltage of just 5 Volts on the left and approx. 2 Volts on the right side of the display, but a current of up to 2 Ampères! The supply circuitry consists of SMD components so small they are hard to see, and they run almost red hot. I have measured 100°C and more. Here is a picture taken just after powering on a mainboard, showing the top-right edge of the board. Behind the display there is at least one transistor, MOSFET or something that heats up pretty bad:

It is likely that one of these components causes the lower of the filament voltages to become unstable which causes the display to look ugly, to fade, or to go dark completely. I have found the following symptoms so far:

• right display voltage ramps up to as much as 5.5 Volts after the PSU is connected. The display initially looks good, then begins to fade. The comparatively high voltage on the right means there is no more voltage drop across the filament which causes the electron emission to stop
• right display voltage is 0 so the circuit is open. No electron emission can take place then

EDIT 2017-05-01: there is a fix available for the former symptom! See here

The left side of the display is constantly supplied 5V. I think the left side is more or less directly connected to the main power supply whereas the right side is sub-regulated, and that regulation circuitry fails.
The hobbyist in us immediately assumes that there are electrolytic capacitors involved which evaporate their electrolyte over time, especially in warm environments. Known issue with tons of old electronic devices, but not in this case. As far as I can see, the circuitry around the display voltage generation does not use electrolytic caps.
Logitech does not make technical documentation for any Squeezebox device open for now, so it is hard, if at all possible, to find out what is the failing component.
There is one more thing to say about Logitech's mistakes: many Boom owners will have noticed that their Boom is pretty warm all the time, even if the unit is in standby and configured not to show anything on the display. This is due to the fact that the Boom keeps the VFD filament powered all the time! Even if nothing is shown on the display and the unit is in sleep mode, the filament power circuitry, besides some more components inside the boom, is constantly powered. Eventually you can switch on the Boom anytime through the Squeezebox Server UI, an app, the IR remote etc. so it needs to be aware and keep parts of its control logic running, e.g. the IP interface, the Wi-Fi board. But is is clear that Logitech did not focus on power saving whatsoever. I assume that the difference between standby and "on" is absolutely minimal. Maybe the power amplifier that supplies the speakers is really off during standby. Everything else is fully powered. That's why the Boom is instantly ready when we tell it to do anything while it is standing by.
This is a thermal picture of my Boom after 6 hours of standby with nothing on the display at all:

The constant "need" to supply the filament voltage surely adds to the aging of the circuitry.
By the way, the filament itself does not contribute to the display aging. While it's a shame the filament is always powered, the display just suffers if pixels are on. So the main concern here is waste of energy.

Tools Needed

What you need for this repair is:

• a T10 torx screwdriver
• a spudger or flat but stable piece of plastic to get off the grilles and remove adhesive pads
• straight pliers
• Noritake MN16032-type VFD glass module (MN16032G is current)
• desoldering station (~ 300 °C, no more than 60W)
• soldering iron with fine tip (~ 285°C, no more than 40W)
• isopropylic alcohol (95% pure or better) to clean things up
• recommended: 3M 08984 adhesive remover  

Tools Not Recommended

The solder pads on the main board should get as little stress as possible. So they should not be heated too much or they will easily come off the board, adding a completely new level of difficulty. So please use temperature-regulated soldering equipment, the reliable / expensive sort if possible.

I do not recommend using solder wick to desolder the old display. It takes too long and will not completely remove the solder in order to loosen the display.

When it comes to cleaning, avoid paint thinner or any other stuff that harms plastic surfaces. It is probably no good for the mainboard, too.

Boom Disassembly

Steps to get down to the mainboard:

1. remove the speaker grilles (left and right)
2. unscrew the control panel, four T10 torx screws (one in each corner)
3. pull the control panel flat flex cable
4. unscrew the mainboard, five T10 torx screws (one in each corner and one in the center)
5. pull the mainboard out

Disassembly: Remove the Speaker Grilles

The grilles are attached to the case with rubber-covered tabs. I recommend using a flat spudger that can be pushed in between the outer case rim and the grille. Take care here because the outer case rim is thin shiny plastic so it is very delicate. You may easily leave marks there that look ugly ever after. So be very gentle and take your time.

Once we're in, lift the grille a bit but do not try to remove it completely yet. Do not use the case rim to crank the grille away because that might ruin the look.

The same needs to be done on the other end. There are also fixing tabs on the outer edge of each grille but they will give way once the upper and lower edge are free.

Eventually this is what you see:

Disassembly: Loosen Control Panel

Next level: let's undo the control panel because it is in the way later. First undo these four TX10 screws:

Disassembly: Undo Control Panel Flat Flex and Remove Control Panel

Once the control panel is loose, be aware that there is a short flat flex ribbon cable in the bottom right corner that needs to be loosened on one of its ends. I find it easier to remove the mainboard-side end of it. This is what you will see when you lift the control panel (gently!)

Edit 2022-05-04: The flat flex cable (FFC) has the same style of connector on both ends. Both connectors are facing upwards, so that is the direction that the FFC needs to be pulled out of the connector. I find it easier to disconnect (and later reconnect) the front-panel side, because there is just more room for doing so, and leave the mainboard side connected. Do keep in mind that the FFC does not like to be connected and disconnected a lot, sooner or later the metal strips will detach at the connecting end(s) and that can cause all sorts of trouble.

NOTE: be sure to just pull the cable out of the connector. Do not rip the entire connector off the board! Because: https://poetnerd.blogspot.com/2020/08/squeezebox-boom-microsurgery.html?showComment=1611480568539#c8879436387643920068

So please make sure not to pull the flat flex any other direction than directly away from its connector, opposite direction of how it was plugged in - and just move in parallel to the board. If you pull upwards away from the board with too much force, you may lift the connector or tear the cable.

Disassembly: Remove Mainboard

With the control panel gone, we see the mainboard in all its glory:

Loosen five TX10 screws in these positions. They are the same length as the four we have already removed earlier. Keep in mind the positions and orientation of the two metal tabs beneath both the top screws:

The ribbon cable in the top-right corner connects the snooze buttons at the top of the device. Pull it out gently towards the Boom's front side as shown here.

The mainboard won't come out easily because the speaker connector on the back is still plugged in. It is positioned behind the left side of the VFD display.
To remove the mainboard, push the backside connection panel inwards, thereby lifting the mainboard. It is recommended to push the right edge out first because of the speaker cable that prevents you from pushing the left edge out as easily. If you feel that nothing is moving, there might be glue between the backside of the board and the case. That is because Logitech production did not have the time to wait for the glue to cure before mounting the main board. Be extra gentle then. Keep pushing with as little force as possible. The glue should tear off eventually. If you are too violent or do this too quickly, the SMD components on the board which are covered by the glue might be torn away.

A little more room can be made by lifting the board on the right side, then pushing it to the right a bit until its left edge can face towards the backside of the case as shown here:

Eventually here is the speaker connector, with the right board edge pointing 90° away from the enclosure. It's a really firm connection and the wires are pretty short so there is not much room to work:

I recommend the pliers to pull the plug out (away from the connector). If that does not fully succeed, you can also try to pull the entire board away - but well-controlled, please:

Preparing the Mainboard

Now that the board is out, we need to take a few steps before the VFD can be desoldered.

First the Wi-Fi antenna that is stuck to the board at the top edge needs to go. It's the metal tab at the bottom edge in the following picture:

Why it needs to go? Because the sticker covers three of the display pins we are going to desolder:

So lift the black tape gently. Make sure you do not bend the antenna:

The antenna is usually glued to the black strip with another black adhesive foam pad which won't come off in one part. So at the bottom of it, you will find remains of the pad which I recommend to remove completely to make way for a new pad:

We will have to scrape down layer by layer. Beneath the foam, a tough layer of adhesive comes up:

This is where 3M 08984 makes things really easy. Just cover the entire pad multiple times and let it dissolve the adhesive. You can also use isopropylic alcohol but it will take more time.

One more layer of adhesive comes off now:

Eventually some spudger work removes the last bits of the adhesive, leaving only the metal. A Dremel will also do nicely. The surface will get scratched on the way but that does not do any harm. The antenna is still going to work as it should. Just ensure that the surface is clean so the new foam pad can hold it properly.

The black plastic strip probably left a paper-like layer on the board. Use adhesive remover or alcohol again to remove what is left:

Later:

Besides the three display pins we just uncovered, there are 15 more pins on the other side. All of these need to be desoldered:

You might find that Logitech has put some glue right on top of the display pins to tuck down the antenna cable. That's unfortunate because that glue is really tough. If you find something like this:

or this:

...be prepared for some extra hours. The upper picture shows a rather mild extent of the problem where only a fraction of the glue blob covers the soldering spots. The lower is rather extreme with at least five pins being completely covered and in need to be excavated.
In this state, it is rather easy to remove the antenna wire. Just perform a careful cut beneath the black wire into the glue material to create a slot through which you can push the antenna cable out sideways. It should not be in the way during soldering anyway.
The problem is that you cannot rip the glue off the board because there is a high risk you will tear off the SMD components to which the blob is firmly stuck. It won't come out as one piece and is potentially stronger than the adhesive that links the soldering pads to the main board material. You will need a sharp blade of some sort, and make sure that you do not touch the mainboard while cutting through the glue blob because you might easily damage traces or SMD components. Violence is definitely not an option here. "Shave" off the blob carefully, layer by layer, until the pins you want to desolder are free.
So far I found that the glue resists high temperatures so you cannot melt it. It will turn black but not go away. It will get a little bit softer though. Dissolving it with some chemical might work but my attempts with 3M adhesive remover and isopropyl alcohol were miserable failures as they changed nothing. So it comes down to a spudger or a blade and tons of patience. You must never slip because cutting any vias on the PCB might come out fatal. I have honestly spent hours with that, which is still better than doing this in a rush and creating yet another brick.
Once the display is out, the surface of this area is flat and thereby easier to work on to remove remaining glue.

Removing the Old Display

The display glass module is stuck down to the mainboard with three adhesive foam pads. You can see two of them at the lower edge of the display. Right edge:

And left edge here:

The third pad is hidden beneath the top edge of the display and is very hard to reach.
You can find the foam pad positions in the pictures coming up.
What is also important to note is the black strip on the upper edge of the display. The purpose of this is to protect the ambient light sensor (you can see it a little to the right or the center in the next picture) from picking up the display light which would distort ambient light measurements and confuse the automatic brightness circuitry, if you ever use that at all (again, I don't recommend it but it's still everyone's own decision).

Remove this strip and keep it for the new display.

Before desoldering the display, let's detach it from the sticky foam pads. I recommend a sharp blade or spudger. Be sure to stay as close as you can to the glass. Do not try to cut the foam pad anywhere closer to the mainboard because you will probably damage or even rip off SMD components hidden beneath the display.
The critical places are shown in the following picture. The display was already removed before, and the top side of the board is actually facing down on the photo. You can see the foam pads (left/top, center/bottom, and the black one right/top) as well as places where SMD components are in your spudger's way potentially:

So again, stay on the glass side when you cut the pads! It's really vital.

Also take care to stay in line of the foam pad. The next picture illustrates how you might accidentally hit an SMD component on the way if you don't stay under the display. As cutting through the foam pads requires some force, you might easily slip or break things. Be gentle and controlled, and take your time for this.

The third foam pad needs to be cut "blindly". Just push the spudger in so it touches the glass and is as far as possible from the PCB. Now that the black tape that protects the light sensor is gone, you can get a good view from the top edge while you cut the pad.
Eventually, the display should come loose like so:

Desoldering time. I recommend using a vacuum desoldering station set to ~300°C with a 0.8mm tip. There is one SMD capacitor that is quite close to the first three pins as shown here:

Try to work around that capacitor. Its plastic base may melt a bit, that's no problem. But try not to bend the capacitor as that would cause a considerable stress to the SMD pads it is soldered to. It can't be good if you happen to snap it off along with its solder pads.
It is hard to show here but I found desoldering easier when the display faces upwards, mostly because you can easily see when a pin is moving free, indicating that all solder around it is liquid and you are ready to remove it. So for each pin, I do this:

• hold the board with the display facing down
• put the desoldering nozzle on the pin to be desoldered
• flip the board around, keeping the nozzle on the pin (nozzle now points upwards)
• keep the nozzle in place until the solder liquefies
• wiggle the nozzle around the pin. The display pin should move accordingly on the top side of the board. As long as it doesn't, stay where you are (should only take a few seconds, otherwise something else might be wrong)
• activate vacuum and keep wiggling while the solder is being sucked away. This ensures that the pin is free afterwards and does not solder itself back anywhere
• if a pin cannot be desoldered, add some fresh solder with a soldering iron, if need be, on both sides of the board. Make sure the solder was liquid on both sides of the board, then retry desoldering

After all pins are desoldered, move each pin to ensure they are all actually free.
An alternative approach is to clip all display pins first (you are probably discarding the old display anyway), then get rid of the glass module and desolder each pin separately. Might be easier because you can then use pliers to pull the pin whilst desoldering it.
Once the display is out, check against a light source. All 18 holes should be free now. If any is clogged, use the soldering iron again to fill it with fresh solder, then remove it all with the vacuum station.

Mounting the New Display

So this is where we are now:

Depending on the state of the foam pads, we can reuse them by putting double-sided sticky tape on top of each like so:

If the foam pads are in a bad shape, feel free to remove them. It is a time-consuming piece of work though. Keep in mind that there are SMD components covered by some parts of the foam pads so you cannot use a metal spudger here. Instead, you will have to use adhesive remover, something soft (plastic spudger, Q-tip, whatever) and a lot of patience again.
The foam pads should be replaced due to the delicate nature of the glass display. It should be stuck down somehow or the display will experience vibration and its pins might wear out sooner or later. So if you removed the pads, try to obtain new ones as close as possible to the specification of the ones you just removed. The thickness is about 2mm, and each is about 30mm x 6.5mm in size.

Apply the black tape to the new display. If needed, use double-sided tape if the adhesive stayed with the old display:

Carefully position the new display on the PCB. Align the pins so they are in a row and have equal spacing between all pins. Insert the pins into the soldering holes, then, while keeping a safe distance from the sticky foam pads, use the white frame that is printed on the PCB to align the display. When you are sure that the position is good, push the display down onto the sticky pads.
Side view before resoldering:

Do the 18 pins, using solder sparingly to avoid shorts. Eventually the pin spacing is only 2mm so using a fine soldering tip is definitely recommended. Do not heat up the pads for too long to protect them from coming off the board.

Final Cleanup

After the soldering work is done, I recommend to remove the flux that is left from the factory assembly of the old display (well, Logitech did not really excel there), and probably also from the solder you just used. Flux is corrosive and some are even hygroscopic which might cause trouble later. Isopropylic alcohol is perfect for removing the flux and won't cause any trouble electrically, plus it evaporates quickly. Use a brush or a toothbrush and generous amounts of alcohol, wipe across the solder pins until the liquid that comes off the board is no longer brown or yellowish but clear.

After cleanup, the site should be nice and tidy:

To reattach the Wi-Fi antenna, I recommend a double-sided sticky foam pad cut to size:

Before you stick down the antenna, ensure that its body will not touch any of the surrounding metal contacts. It should be centered between the contacts next to it in all directions. The following photo shows it between the first group of three pins of the VFD on the left, and the three contacts of the IR receiver diode on the right:

Eventually, the inside of the control panel's screen should be cleaned up so there is no distortion from it. Over the years, the screen collects some fine dust that covers the entire inner surface and might lead to a milky / blurry vision. This is a good opportunity to remove all dirt from it. You may need multiple passes with a soft cloth and alcohol. No worries, there is no coating on the screen. But please ensure that the material you use does not cause any scratches and won't attack plastic surfaces by any means. Paint thinner for instance is sure to ruin the job.
The picture illustrates how smears from a previous cleanup attempt remained and can be seen against light:

These smears will be illuminated by the display and we just don't want that. Just keep on cleaning until all that crud is gone. It will improve the experience even more.

Notes on Reassembly

Verify Everything

As we get closer to the first power-up after the repair, it's time for a full check of our work:

• Check all solder connections for shorts and cold joints. A continuity tester is great for this. The groups of three pins on the left and right side of the display have the same potential so it is okay if they appear shorted. But no neighbors among the remaining 12 pins should be shorted
• If you find that the solder on a pin looks dull, or the pin can still move, heat the connections in question up another time
• If you want 120% safety, measure each display pin against the respective trace on the mainboard to see if any connection is not actually working
• Ensure that the reattached Wi-Fi antenna does not have direct contact to anything

Speaker Cable

As before, there is not much room to move the speaker connector back where it belongs. So place the board with its left edge facing the main board recess in the case so the connector and plug are close together. Then align them and push them together with the pliers. It is very hard to do this by hand. The connector may seem fast but actually it might still be loose, later causing dropouts and distorted sound. If you use pliers, it is much easier. Squeeze until the connection clicks into place:

The speaker cable can be pulled out of the casing by some millimeters which gives you more freedom. But consider that there is not much room to stuff the wires away eventually so keep the wires as short as possible.

Sanity Check

After mounting the mainboard might be a good time to verify the results of your repair progress so far. Even though the control panel is not yet attached, you can power up the Boom. Just observe whether the display lights up bright and shiny after a maximum period of 5 seconds. If it does, see if the board passes the boot sequence. You may use the IR transceiver, the mobile app or the Squeezebox Server interface to play some music for verifying that the speaker connection is intact. If everything works, congratulations! You are practically done. Just unplug everything for the final assembly.
If the display stays dark, you hear noises, smoke comes out somewhere, detach the power supply as fast as possible. Let's just hope this never happens. There is no technical support for that situation.

Mainboard Fixing Screws / Metal Tabs

Make sure you place the metal tabs the way they were before. Note that the top-right metal tab pushes down on the snooze button ribbon cable so the cable must run beneath the metal tab, not across:

Please make double sure that the unit is not powered while you put the screws and metal tabs back in. They are electrically conductive and any shorts on the mainboard are probably fatal.

More Information

You might have noticed that some photos and part of the disassembly / reassembly instructions is familiar. I have copied it from my other blog entry about how to repair the bass woofers of the Boom. See here if you are interested: Bass Repair

Final Words

Some legal stuff because you never know: please bear in mind that I am writing this as a hobbyist, not a professional. I describe personal ideas here which is only one of many ways such a repair can be achieved. I cannot guarantee that following this guide will lead to a good result, and cannot be held liable for any personal, physical, or monetary damage anybody suffers by following this guide.
I am open to advice if anything described here is wrong or can be done better. Please let me know in the comments if you find there is anything left to be desired.
Thank you!