Logitech (Slimdevices) SqueezeBox Classic (SB3) Capacitor Refresh

Hey all,

another informational article about the Squeezebox Classic a.k.a. SB3! Slimdevices project name was "Willy" by the way ;o)

After 10 to 12 years in service, the time is now coming for a lot of SB3 units to fail due to aged capacitors. If you have an SB3 that reboots frequently, especially when playback is supposed to begin, there is a good chance that replacing a few capacitors might solve the problem for good.

Most of the failures seem to happen around the DAC. That explains why a Squeezebox might be perfectly operable and configurable but fails as soon as it should begin playback. I cannot prove it but my theory is that the DAC becomes unstable due to bad capacitors, and communication between the DAC and the Xilinx FPGA gets erratic as well. This might propagate up to the CPU which attempts to resolve the issue by restarting. That of course won't help if the hardware has an issue.

There appears to be a design flaw as well that causes two capacitors to go bad prematurely because they are supposedly mounted in reverse polarity in production. We will take care of this matter, too.

Some issues and instructions can be found in the sibling article, e.g. how to open the SB3 and get the board(s) out: https://joes-tech-blog.blogspot.com/2018/11/logitech-slimdevices-squeezebox-classic.html

Compared to other Squeezebox models, there are a *ton* of SMD capacitors on the board, 23 in total. In many cases, the majority of them have to be replaced. But there are ways to check each one carefully and replace one by one until the unit is stable again.
But a word of warning first - copied from the article mentioned.

CAUTION! I must warn y'all that wearing a ESD grounding strap or similar, and using ESD-safe equipment is imperative when working with the SB3. It's notoriously sensitive to even small discharge events which immediately turns the unit into a precious paperweight. Be sure to be connected to ground at all times when working with the innards of an SB3!

I suggest you check out the article to see how to open the device. I won't repeat it all here, so we start at the point where the board is outside the case.

Measuring Tools

The component and ESR (equivalent series resistance) tester from ELV shown below is a great help in spotting defective electrolytic capacitors. It can be purchased as a DIY kit, or fully assembled at a higher price. Certainly there are other tools capable of doing the job. Be aware that an ESR meter cannot easily be replaced by a standard multimeter as the series resistance of a capacitor is not what you would measure in the Ohms range with a multimeter. The ESR meter applies a clever combination of charge, frequency and current to figure out the Ohms equivalent of a capacitor *in circuit*, i.e. no need to desolder suspicious components! In many cases, the in-circuit measurement already points out the bad capacitors pretty well, however, not in all cases.

 

 

The ESR value is not the whole story about a capacitor's health but it gives a good indication. Basically, the ESR value should be very low, typically less than 1 Ohm. There are tables published by the manufacturers where you can find out what range is good. Generally, if a capacitor measures clearly more than 1 Ohm in circuit, that might be a bad sign already. In my experience, high resistance values indicate failed caps rather than low resistance values prove a cap is still good. A low resistance can also result from the circuitry around the capacitor. But in many parts of a circuit, the capacitors are where the ESR is pulled to a low value, and if a measurement is too high, it probably means there is an issue with the capacitor under test.
So again, the ESR meter helps but you may find that even though you replaced all suspicious capacitors (by means of bad ESR values), it still isn't enough to resurrect the SB3. In that case it might be easiest to replace them all. Eventually a complete new set of capacitors costs as little as 5 EUR / USD, and having them all before the repair starts is advisable anyway.

As capacitors are really not that expensive, you can do away without an ESD tester of course, and just replace all of the caps for good. It will be more work on your side though.

Capacitors on the SB3 Mainboard

Here is a chart of all SMD capacitors. The respective type can be identified by the color. Polarity is indicated with the black half-moon shape which is the negative terminal. The silk screen shows the following shape for a capacitor:

The left bar is negative, and the side with the 45-degree corners is the positive terminal. The little "+" sign is not actually printed onto the board, it is shown here for clarity. You will find the same outline on the base of unipolar SMD capacitors which helps in the placement.

Following is a reference of the SB3 board with all capacitors highlighted. Note that the polarity is shown by the black half-moon shapes which indicates the negative terminal. SMD capacitors typically have a similar indications of the negative terminal as part of their marking.

 

The colors can be used to identify what voltage / capacity combination is used where. I have added the

capacitor numbers in white-on-black on top of each capacitor because the silk screen on the board is a bit unclear in places, and some of these markings are hidden under the Wi-Fi antenna on the far right edge which I have only removed for the photo.

What is new, compared to earlier versions of this blog, is the bipolar capacitors used in two places instead of the regular unipolar 16V/10µF ones of the original design. This is a consequence of some discussion in the forums where some people claimed that C16 and C20 were reversed in production.  Even the silk screen is supposed to be reversed. This can't be good as unipolar capacitors get damaged in reverse polarity condition. Apparently there is no significant power involved in that area so they can withstand this situation for quite a long time but certainly not forever. I think the claim about reverse polarity is accurate as I have found many C16 and C20 had leaked when I removed them for renewal, whereas others might have had bad measurements but at least contained their electrolyte.

As I am not quite sure whether C16 and C20 must be put in disagreement to the silk screen to give them the proper polarity, I have evaded to using bipolar electrolytic capacitors. They have similar properties as their unipolar siblings but their construction allows for any polarity.

Parts List

Resulting from the picture above, you need these parts if you plan to re-cap the SB3 completely:

Amount	Voltage	Capacity	Diameter	Height	Places
7	16V	220µF	6.3mm	~8.0mm	C7, C9, C32, C35, C42, C49, C67
8	16V	10µF	4.0mm	5.5mm	C6, C12, C17, C21, C23, C52, C53, C57
2	16V unipolar	10µF	5.2mm *)	6.0mm	C16, C20
3	50V	1µF	4.0mm	5.5mm	C15, C36, C39
1	50V	2.2µF	4.0mm	5.5mm	C5
1	16V	47µF	6.3mm	~5.5mm	C47
1	63V	22µF	6.3mm	8.0mm	C74

*) be aware that bipolar capacitors might be a bit larger. The ones I have in stock are 5.2mm diameter instead of 4.0mm that the original ones had. So it gets a bit crowded when soldering them in as they are larger than the designed footprint. Be careful to choose capacitors that won't exceed 5.5mm diameter as it will be very hard to solder them in.

While the width should not be exceeded too much due to space restrictions, the height of each capacitor is not actually significant. As long as your replacement capacitors stay below 10mm, it should not be a problem.

I have deliberately left out the two through-hole capacitors (C58 as well as the blue one wedged behind the connector PCB that has no number on the mainboard and is probably some kind of configuration item. These capacitors have never failed in any device on my bench so I guess they don't need to be replaced.

 

Repair Procedure

Once again, be sure to be ESD-safe at all times.
In the past, I used to replace a capacitor, then power up the SB3 and see whether it is better than before. This failed a few times though and left me with a dead unit. So this procedure might be too stressful for the precious device.
Since then, I basically take two steps:

1. do ESD measurements to isolate the really bad ones, and replace all of them. Then power up and see if there is an improvement
2. if not (or if you want to be extra sure): replace all of the remaining SMD capacitors not touched until this point

It might be advisable to remove the CPU board during the repair. This is easy if the adhesive pad already gave way. These pads are sturdy though, and even after ten years they may cling on quite a bit. Be really careful not to damage the board-to-board connector when you try to pull the CPU board out of its socket.

The first attempt to desolder the SMD caps gave me a bad headache. I lifted almost every second pad because it is really hard to heat up the entire capacitor's legs far enough to melt all the solder, most of which is hidden beneath the capacitor's base. This is an enormous stress for the pads.

Using a heat gun is possible but may cause a lot of stress for the board itself, and plastic parts may suffer from the heat. It's also far from being a warranty that the soldering pads are not accidentally torn off.

A better way is shown in the following video by Mr. Carlson: https://youtu.be/X8N9O3a9jiM

Even though one should think that the mechanical stress to the soldering pads is just as bad in this method, the absence of heat is a very good thing, and I rarely lifted a pad accidentally using this method. It's a bit risky if the capacitors have leaked as that weakens the pads, too. But even if you rip one or two pads, that's still well repairable.

So that method is definitely recommended. You will find many times that the remains of the capacitor legs are still on the pad and need to be desoldered individually, but as the soldering point is completely exposed, it is easy then to heat it all up quickly for cleaning up.

Putting in the new capacitors is a matter of taste. Some prefer solder paste and heat which is close to the original manufacturing process. Put solder paste on both pads, then stick the capacitor(s) on top of the solder paste beds, eventually apply hot air (slow air speed but high temperature) to have the solder paste melt into flux + solder consistently. It will look great if you do it right, almost indistinguishable from the original manufacturing result.
Of course, it's also possible to hand-solder the new SMD capacitors. Won't look that beautiful but works a treat. I usually pre-tin the pads and put some flux to ensure the solder will liquefy and connect to the capacitor's legs properly. It will also make the solder shiny and more robust regarding future corrosion. Start on one side and once that is fixed, heat the other pad and push the capacitor down, keeping the soldering iron in place to ensure that the solder on the leg and on the soldering pad will combine. For perfection, heat up the pad you did first again and push the capacitor down on that side, too, so it sits as flush as it can get.
A real SMD soldering iron with two thin tips will do this job even better. It's very expensive though and requires some exercise, too.

 

Some more advice:

• C21 and C23 are probably the hardest to work on because they are behind the RCA and (plastic) headphones connector so you will have to be careful not to burn the 3.5mm headphone jack. If you are a perfectionist and own a good desoldering station, you may desolder the 24 pins that connect the main to the connector PCB so you have more room to work but that is usually not required. Just be careful not to burn anything and ensure that the connections that are least reachable are solid.
• C35/C32: solder pads for the negative terminals are very close together. It may be worthwhile putting both a little outside their footprint to ensure you have enough space between them to solder the center legs
• C47/C42: same here, there is a common connection between both caps, and there is not much room to heat that up. Even worse, the negative of C42 is partially obstructed by the power connector. I usually place C47 a little further away from the center, then solder C42 positive pin first and eventually the hard-to-reach negative pin. Wiggle the cap eventually to see if it is actually firmly attached on both ends
• C74 has the display's high-voltage driver close to its negative terminal. Place it a bit further away from the chip than the silkscreen indicates so you can properly solder the negative terminal without damaging the chip that is close by
• the large 3300µF capacitor can be bent outwards in case it is in the way of your soldering work. Eventually it should be bent back, and I recommend fixing it with some hot glue underneath to relieve the solder connections from bearing the entire weight alone
• before you power up, double-check that all capacitors are
• firmly attached
• placed correctly regarding their polarity and values - it is very easy to confuse the 10µF, 1µF and 2.2µF due to their minimum size
• if you removed the CPU board for the repair phase, you will probably find that the adhesive strip that held it to the board is no longer sticking as well as it did initially. However, it is important that the CPU is held in place not only by its connector. In doubt, use some hot glue to reinforce the sticker. Be aware though that there is not much space in the housing. Excessive use of hot glue will lead to a PCB that you cannot get back into the case
  

Small anecdote here, I ended up fixing the board where I lifted all those pads by using standard through-hole capacitors whose legs I routed to connect each to the right spot on the board, then glued them down with hot-melt glue. This isn't actually beautiful, and a lot of care is needed about the space taken up by the through-hole stuff, eventually it is much larger. It was hard to put the components in places where they would not collide with the backside of the case where board sits in when mounted. The positive side is that through-hole capacitors are much less prone to fail than their SMD siblings. So while it was a pain to repair, the SB3 that suffered so much from my bad beginner's SMD soldering "skills" is now the most reliable in my collection. Go figure...

So far so good. Hope that does it for now. Let me know if you think anything is missing.

Thanks for reading, and as always, good success on your repairs!