Amiga Memory Expansion Fix

[EssexMame]

Hi,

[This might be slightly off topic but it seemed to be the best-fit forum. Please move if not]

I have an Amiga A500 with an (unofficial) expanded memory board. It contains a battery backed up clock and this battery (NaH 1000?) has leaked, causing some damage to the board. It is slight but some of the copper is green/corroded and the board is not working.

I'd like to repair it if possible, and I'm sure I can get a replacement battery of some sort. However, how simple/possible is it to repair the copper tracks on a circuit board? It is quite simple to see which are damaged but is repairing them possible at home? I'm not experienced at all, outside of a few simple solder repairs a few times but I know some of you guys are so I thought I'd gauge if it was a (fairly) simple process.

What could I use to clean the circuit in the first instance - meths?

[lilshawn]

it's seems like a simple enough circuit. just neutralize the "acid" damage happening now by using vinegar. (the battery "acid" is actually sodium hydroxide which is an alkaline "base", not an acid. (which is where the term alkaline battery came from))

once you have it cleaned up, check the traces with a meter. you can use a small jumper wire to bridge together any broken tracks.

you may find once you clean up the leakage, it may start working again. (the electrolytes are pretty conductive)

you needn't replace the battery, just remove it. it's just for the realtime clock...and it's not really necessary in this day and age.

just make sure the board is clean and dry before attempting trying it.

[Admiral688]

I have an old 500 in the basement with a broken floppy drive, otherwise it's perfect. Is there a modern add on for a hard drive type of setup??

[lilshawn]

it's got a serial port. you'd have to find a DB25 to DB9 adapter and an external modem, but i'm pretty sure it would work.

failing that you could find some software for the windows pc that can set the serial port to emulate a modem on the serial port... then you'd just need a crossover cable to connect them together.

from there it's up to you what else you need to do. I never had "internet" (as it were in those days) until well into the 90's near the end of the BBS era and we all started going PPP.

[EssexMame]

Thanks Lilshawn - very helpful - I'll give it a go at the weekend!

[EssexMame]

Is this the type of circuit tester I'd need?
http://www.amazon.co.uk/Rolson-28169-3-in-1-Circuit-Tester/dp/B0013KB6Z4/ref=sr_1_2?ie=UTF8&qid=1424255425&sr=8-2&keywords=circuit+tester#productDetails

and what of the small jumper cables (if needed). Just any short/thin length of plastic coated copper wire?

[lilshawn]

something more like this:

http://www.amazon.co.uk/DIGIFLEX-Testing-Digital-Multimeter-Voltmeter/dp/B003NEGZLS/ref=sr_1_4?ie=UTF8&qid=1424277736&sr=8-4&keywords=continuity+tester

you aren't going to do this with the board powered on, you are going to take it out and test it on your workbench.

you need to test for "continuity" between the legs on the chips and wherever they go. basically, you want to pick a leg on a chip and follow the copper trace on the board until you find then end where it connects to the next part and test if the meter shows that it's connected between those 2 points. (beeper beeps and/or reads zero ohms of resistance)

continue through all the damaged areas and note any that should be connected but are reading as open or high resistance. (all traces should read zero ohms)

install wire jumpers between the components where the copper traces are broken. any small diameter wire with a plastic insulator on the outside will work just fine. Don't go too big because it becomes difficult to solder it onto the components, especially if they are small. avoid uninsulated wire (bare wire) and you should probably avoid enamel coated wire. it is difficult to work with if you don't prep it properly.

check your continuity again and make sure you haven't bridged any places that should not be with solder or stray wire.

[EssexMame]

Thank you! I've cleaned up the board with vinegar and though it looks slightly better it's still not working so I'll get a multimeter like the one you've shown and see where I need to add some wires to replace the broken ones

I'll try another clean too - should I leave the vinegar on for a bit to let it work against the alkaline?

[lilshawn]

You shouldn't need to go too crazy. If the vinegar is no longer reacting to the board it should be okay. You mentioned you have a clone of the module. I'm not sure how it's laid out, but with the legit board an IC is directly under the battery. If it's similar, you will have to flush out under the chip...either by removing it or carefully using a syringe or dropper to flush out the battery residue. IC's are difficult to remove without proper equipment. Mind you, the part is small enough that I would personally remove the battery and place the entire board in a shallow plastic tray and rinse it freely with vinegar. Followed by a rinse with clean water. I'm also a little crazy but since its not working to begin with, there is not much to lose.

[jackiabu]

Is the damage to the board you mean the A500? or the expanded memory board? 

can you put some pics here?

[EssexMame]

The damage is on the memory expansion board.
I'll add some pics, sure. The vinegar etc hasn't done the trick and I'm struggling to find a problem using the circuit tester also.

[lilshawn]

it's not going to look brand new, the board is damaged from the battery. you just need to stop the damage that is currently happening and then fix whats been damaged. it not pretty, but it will work.

[matsadona]

I have an old 500 in the basement with a broken floppy drive, otherwise it's perfect. Is there a modern add on for a hard drive type of setup??

https://cortexamigafloppydrive.wordpress.com/

[EssexMame]

it's not going to look brand new, the board is damaged from the battery. you just need to stop the damage that is currently happening and then fix whats been damaged. it not pretty, but it will work.

thanks lilshawn - I didn't have much luck with the circuit tester finding what didn't work. There are plenty of paths to check though so I guess I wasn't going to find it instantly. i'll have another go at the weekend. I did wonder if, with the battery removed, I still needed to complete the circuit there - i.e. a wire from + to - where the battery would've been.

[matsadona]

I did wonder if, with the battery removed, I still needed to complete the circuit there - i.e. a wire from + to - where the battery would've been.

Do not do that!