Monday, October 11, 2010

[Amiga] A2000 Battery Recovery

This is another repeated article from www.amiga.org.

Hi people,

in case someone needs to repair some damage done to the Amiga 2000 mainboard by a leaking battery, this is the right place for you.
Found that A2000 on eBay a few days ago. It was sold as defective and would not power up. Obviously, the seller didn't know too much about the computer, but I took the risk and got the item for about 45 EUR. Not too much loss if it was irrepairably broken.
It's a fascinating machine, pretty large and with a lot of space inside, so I won't ever need to think about heat dissipation like in my two A3000 models. In comparison, they are pretty crowded and less maintainable. The A2000 features the largest PCB of all Amigas (it's actually huge, about 4 times an ATX mainboard), and except for Agnus who is PLCC, all custom chips are still DIP-shaped like in the Amiga 500. A lot of Zorro slots provide great extensibility, and I was happy to find a Kickstart 2.0 ROM in there. Not much more though, no RAM expansion, no hard disk drive or anything else.
I have made an attempt to repair it today as this was another battery leakage victim like most of the Amigas who boast an RTC. The battery has done some bad-looking corrosion to the mainboard, and as the CPU socket is quite near to the battery, it was affected, too.

Tools needed to do this repair:

  • soldering iron (mine is an Ersa Multitip 15 Watts, about 25 years old)
  • some solder wire
  • unsoldering tool (I used a cheap one-shot-and-reload vacuum pump with a silicon tip)
  • multimeter to check that the PCB connections are still okay
  • in my case, a new 68000 socket (DIP-64)
  • (later) a button battery (CR2025 or CR2032) and an appropriate clip
  • (later) a diode for the new battery to prevent destructive recharging attempts by the board
And here's what I did:

  • completely disassembled the A2000 to find a 5,25" drive inside that does not connect to the board directly. Obviously some freak has converted a former external drive into an internal one, also keeping the adaptor PCB and a lot of cable straps, sigh... the connector cable needs to go out of the case to the external floppy port... ah well, that's going to be a different thread. I don't think I can bear this for long :-D
  • removed the mainboard from the case and cleaned it a little. Some big flakes of dust have accumulated there over the years
  • removed the battery (sorry, no pictures here) and thoroughly cleaned the PCB in that area. I noticed that the PCB is pretty delicate when trying to unsolder. The solder mask becomes damaged when exposed to too much heat for too long (and in this case, I think it is lots shorter than usual), and probably one would easily kill leads unless being extremely careful. Maybe the board's age adds to it.
  • checked damage done by the corrosion. Nothing seemed to be actually broken and no leads seemed disrupted by the corrosive process. I sure hope it does not continue in the future.

The old battery after removing. I can't understand how Commodore could be so stupid as to place batteries directly on the board with no socket. Sigh... well, that seems what everybody did those days.




Notice the dark spots left by the corrosive. It has come pretty far and even dug along under the battery lead. The CPU socket shows traces of corrosion, too. See the greenish pins 1 to 6. I think this is the main reason the A2000 has failed (probably no good contact anymore)

Different angle
  • I decided it's hopeless to clean the socket, plus I wouldn't get a chance to see if anything is broken beneath the socket, so I removed it completely. As unsoldering this item without damaging the board is near impossible, I broke the socket frame and pulled the plastic parts of it away from the board, leaving only the metal pins.

68000 socket, no plastic frame
  • then I unsoldered all the pins one by one while pulling them away with a pair of pliers on the other side. That worked pretty well but left the soldering eyelets closed in most cases.

Socket debris
  • to make unsoldering easier, I put some solder on all the eyelets so they would heat up more quickly on both PCB sides
68000 socket eyelets prepared for de-soldering

  • after unsoldering, a visual check of the board against outside daylight offered no obstructed eyelets:

Shiny!
  • this was a good time to do some measuring on the leads in the area affected. As it seems, all are fine, no leads broken. I scratched the masking paint from the place where the battery cathode was placed to see what has happened there. See the bluish touch of that beastly stuff?
Socket gone - blue traces of battery sludge beneath the masking paint

  • now I inserted the new 64-pin socket and fixed it
New 68000 home from the PCB bottom


68000 replacement socket top view


Mind the copper lead I found where the battery was. Obviously there was no actual damage although the lead may have been thinned out considerably.

68000 in place again

68000 edge view

After connecting to the PSU and floppy, I carefully started the machine for the first time since I received it. The Kickstart screen came up and first attempts to load disks were successful! Yippieee, day saved! :-)

There are some things to do though. As I don't have a button battery and socket handy, I will have to do that replacement later. Maybe I'll post some photos about that, too.

Hope you liked this A2000 revival story!

Have a nice day,

Joe

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