Wednesday, May 18, 2016

Death by Rechargeable Battery

Any Amiga afficiandos amongst you will know that, back in the day, Commodore had some funny ideas when it came to upgrading the Amiga. First, the A500 came out with Kickstart 1.2 which was upgraded some time later to Kickstart 1.3. This was the de-facto Amiga A500 for a good number of years.

Then, in 1991, like all good buses, two upgrades (well one upgrade and a cancellation really) came in quick succession. First, the A500 had a boost to the A500+. It came with a whole 1Mb of RAM and the shiny new Kickstart 2.04 which was similar to the big brother A3000s ROM. Very soon after, for some bizarre upper management reason (i.e. complete incompetence) the A500 was scrapped and replaced with the A600.

I won't debate the merits of the A600 (or A300 as it SHOULD have been - I seem to recall the manager responsible for the A600 was fired) but instead focus on the A500+. This machine holds a special place for me since it was my first Amiga. I had an early A500+ and the white box it had said 'A500' (no 'plus') in the Cartoon Classics pack so I had no idea it was a A500+ until I actually took it out of the box.

One additional feature of the A500+ was the built in real time clock. This may seem quite quaint these days but back then, this was the height of 'ooooh!'. To power the clock a small battery was factory fitted to the motherboard. For the market life of the machine there were no problems and we all enjoyed having accurate dates and times on our files.

Fast forward 25 years.

Retro computing is gaining in popularity. Amiga computers are popular with collectors and retro gamers as they're pretty reliable and, well, cool. But there's a problem. Remember that little barrel battery on the motherboards of the A500+? Well, what do you think batteries do if they're left for years with no use, no voltage, no current and no charging? They leak. What do batteries contain? I will give you a clue. They do not contain rainbows and unicorns. They contain liquid death.

The story normally goes something like this. You see some article on how retro gaming is popular. Prices for systems are rising. Hmmm. You used to have an Amiga. Maybe it's in the loft/garage/shed? You dig it out. Yes, an Amiga A500+. You plug it in. You turn it on to see if it still works. Green screen. Or black screen. Or slowly flashing power LED. At this point a lot of people might throw it in the bin (NO DON'T!) or pop it on the table at a car boot sale for a couple of quid. The braver souls might open the case and peer inside. They might see something like this:

What's that green stuff?

More green stuff..

That green stuff is corrosion caused by the battery spewing its contents all over the motherboard. The first thing is to remove the battery then cover the affected parts of the board in lemon juice (really). It neutralises the corrosion and fizzes nicely while doing it. Then, wash the area with isopropyl alcohol and leave to dry. Sometimes the board has been lucky and the damage is limited. Sometimes it's too late. :(

Just to be clear, the batteries in these things have a life of up to about 6 or 7 years if you're lucky so there is no blame here. These things are now 25 years old. It's just a fact of life if you have an Amiga A500+ (or 4000 or 2000 actually).

The point of all this is that I took a gamble on a cheap A500+ motherboard from ebay. The seller said that it didn't work as the battery had leaked. Looking at the photos the damage didn't look too bad - not that you should trust the photos. So, a few days ago I received a package.

After cautiously unwrapping it, I found this:

Shielding included (didn't realise it was!)

The Patient
First things first. Let's check what the damage really looks like. At first glance, it's actually not too bad. Someone has attempted to clean up the board and the battery has been removed. The damage is still obvious though. 

Corrosion everywhere :(
Next, lets plug this baby in. The screen turns white then almost instantly shows solid green. That's not good. It means that there's a problem with the chip RAM but could mean that it's the RAM that's faulty or any of the components between the RAM, CPU, ROM and custom chips... This will take a bit of work. 

OK, so now we inspect the board a lot more closely. I cleaned off as much of the green corrosion as I could, partly by scraping with a scalpel and partly by using isopropyl alcohol. Not as good as lemon juice but it did the job for what I needed. Next, a lot closer look at the tracks that are in the firing line:

There's one definite break (possibly more)

Close up of 4th pad down on top picture - definitely unhappy

A clean break - no copper left here at all

By using the continuity function on a multimeter I confirmed that there were two traces that definitely had problems. These were from the 'south' end of R101 to the via and from the 'south' end of R112 to the via. As it turns out, there was a third issue from the 'south' side of E102, as it runs past the leg of the EVIL KILLER FROM HELL - er I mean battery. 

For the resistor R101, I could not find where the break was. It was most likely that the trace had multiple tiny breaks, making it impossible to just use a sliver of wire as a track repair. In the end, I installed a jumper from R101 to the via. 

For the resistor R112, things were a bit more straightforward. I used a stripped piece of 30awg wrapping wire, about 6mm long and bent into the right shape to bridge the gap from the track to the via.

Finally, I used a straight piece of the same wire, again about 6mm long, to repair the straight trace that had been damaged next to the battery leg.

The results look like this:

Wire added from broken track to via - jumper visible back to R101

Connection to R101 - not the neatest but it's connected now

Track repair next to the battery leg (battery removed)

Before I could test it I realised that the trapdoor connector had suffered badly too at the hands of the evil battery. The pins had corroded badly and there was nothing I could do to save them. I had to remove the entire connector. :(  Fortunately, they are available new. Yay! :)

Connector still attached but looking poorly...

Connector partly removed - not looking any better

Pins cleaned up to illustrate the damage batteries can cause
So, with all this done, time to plug it in and see if there is any improvement. Why, yes, Yes there is. :) 

Another A500+ saved from the bin

There is still a lot to do on this but the worst of the problems are out of the way. Stuff that needs doing:
  • Test the whole thing
    • Floppy drive
    • Sound
    • Keyboard
    • All ports
  • Replace the trapdoor connector
  • Buy a case, keyboard and floppy...(remember I only bought a faulty motherboard!)
I will update you all soon once I've carried out more tests, but so far, it's looking good.

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