A500 issues

Vypr · 18 January 2019, 14:54

I recently picked up an old A500 for a cheap price on eBay. It was sold by a company that picks disposes of unwanted electronics so it was just the A500.
The machine itself was quite grimy and looked like it had sat in a garage or loft for a number of years but the asking price was pretty low (£45) so I thought I'd give it a shot.

On receipt of the machine I opened it up to take a look. It had an A501 RAM expansion, a Rev 6A board and a dual kickstart board fitted :

I removed the A501 and checked it, the battery leak was quite bad and appears to have killed the board.
Also, there was some quit heavy corrosion on the expansion port pins:

I removed the memory chips from the A501, replaced the expansion port pins and soldered them onto the main board along with a switch I could use to choose between 1Mb Chip and 512Mb + expansion memory.

The machine will boot up Ok but after a few minutes will become unstable and crash and then refuse to boot unless it has powered down for a while. When it doesn't boot it goes to either a yellow or green screen.

I fitted a DiagROM which showed the CIAs & IRQ lines were fine. memory tests fail at the last few bytes of the chip RAM test, regardless of if the added on RAM is enabled or not :

Also if I plug in a known working A501 board, initially memory checks show no issues but after about halfway, errors start cropping up.

I tried with a A1200 PSU and an ATX supply with an adaptor and got the same issues. I then recapped the board. The system is a lot more stable now and the extended RAM on the A501 now reports no troubles on the RAM test. The chip RAM however still fails the last 4 bytes (specifically 7FFFB to 7FFFF)

Is there anyway to identify which chip on the board is the suspect one?

lesta_smsc · 18 January 2019, 20:34

Not sure if systest could identify the chip in question? It seems to run through the banks of chips one after the other...

dalek · 01 February 2019, 07:21

you could remove the expansion chips you added. With one of the spare chips, piggyback the first ram chip on the motheboard and test. Power off an repeat for each of the other chips. If the problem goes away you know which chip to replace.

ramparts · 04 February 2019, 01:43

Wash board with isopropilic alcohool

18 January 2019, 14:54	#1
Vypr Registered User Join Date: Dec 2016 Location: East Kilbride, Scotland Posts: 451	A500 issues I recently picked up an old A500 for a cheap price on eBay. It was sold by a company that picks disposes of unwanted electronics so it was just the A500. The machine itself was quite grimy and looked like it had sat in a garage or loft for a number of years but the asking price was pretty low (£45) so I thought I'd give it a shot. On receipt of the machine I opened it up to take a look. It had an A501 RAM expansion, a Rev 6A board and a dual kickstart board fitted : I removed the A501 and checked it, the battery leak was quite bad and appears to have killed the board. Also, there was some quit heavy corrosion on the expansion port pins: I removed the memory chips from the A501, replaced the expansion port pins and soldered them onto the main board along with a switch I could use to choose between 1Mb Chip and 512Mb + expansion memory. The machine will boot up Ok but after a few minutes will become unstable and crash and then refuse to boot unless it has powered down for a while. When it doesn't boot it goes to either a yellow or green screen. I fitted a DiagROM which showed the CIAs & IRQ lines were fine. memory tests fail at the last few bytes of the chip RAM test, regardless of if the added on RAM is enabled or not : Also if I plug in a known working A501 board, initially memory checks show no issues but after about halfway, errors start cropping up. I tried with a A1200 PSU and an ATX supply with an adaptor and got the same issues. I then recapped the board. The system is a lot more stable now and the extended RAM on the A501 now reports no troubles on the RAM test. The chip RAM however still fails the last 4 bytes (specifically 7FFFB to 7FFFF) Is there anyway to identify which chip on the board is the suspect one? Attached Thumbnails

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18 January 2019, 20:34	#2
lesta_smsc Registered User Join Date: Feb 2012 Location: United Kingdom Posts: 3,173	Not sure if systest could identify the chip in question? It seems to run through the banks of chips one after the other...

01 February 2019, 07:21	#3
dalek Registered User Join Date: Nov 2014 Location: NSW/Australia Posts: 462	you could remove the expansion chips you added. With one of the spare chips, piggyback the first ram chip on the motheboard and test. Power off an repeat for each of the other chips. If the problem goes away you know which chip to replace.

04 February 2019, 01:43	#4
ramparts Registered User Join Date: Apr 2011 Location: porto/portugal Posts: 50	Wash board with isopropilic alcohool

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