White Screen on an A500

[russellnash]

I decided to do something unusual today and fetched my Commodore Amiga A500 out of the shed. I was trying a few disk images selected at random on the Gotek and it was working fine. I selected Dragons' Breath and booted it up. Funnily, it gave me a strange anti piracy screen a bit like those really annoying things you used to get at the start of video cassettes back in the good old days, then it disappeared and the screen shortly afterwards went white to light grey, it is not so easy to say because there is a lot of sunlight coming into the room today. So, I did a reset and that is all I get now. That was some great technology they had which could zap your computer. :D
I have reseated the socketed chips, which all look clean and that did nothing. One thing is, if I disconnect the 1mb RAM the screen becomes yellow, update, it is yellow for about 9 seconds and then goes dark for about one second. Can anybody point me in the general direction of what causes this symptom? I can't seem to find anything about it on the forum when I do a search. I will post a photo later. Thanks

[rubber_jonnie]

It could be power, do you have another PSU you can check with or can you check the power with a multimeter? If you disconnect the Gotek does it boot?

Also If you can get a disk image of Amiga TestKit it would be worth trying, also a copy of the Amiga Diagrom may help here.

Also may be worth removing the IC's including Agnus and giving the sockets a scoosh with contact cleaner.

[russellnash]

I will test the power supply now I have looked at the pinout. It is a bit fancier than on an ST. It doesn’t boot without the Gotek. I sprayed contact cleaner on the sockets straight away, but they all look so clean I thought it was unlikely to be that. There was battery corrosion from the RAM upgrade when I received it about 3 years ago and various traces around the expansion socket area have dark corrosion patches. Thanks.

[mrbombermillzy]

Oh dear. I hope its not the dreaded green ooze working its black magic. :(

[mrbombermillzy]

To help people here better diagnose the board, can you take any photos?

That green battery damage can creep up tracks, ICs and get everywhere, destroying all in its path.

You may need to neutralize the board before taking any other steps to avoid further damage.

[russellnash]

a500.jpeg

I am going to resolder pads in the area left of the top half of the RAM upgrade connector.
Originally the machine seemed to start fine but I opened it up when the floppy drive wouldn't consistently read the Workbench disks that I bought. Most of the green stuff was not on the mainboard but I had to bash the the RAM upgrade off with a wide screwdriver and hammer to get it to move.

I resoldered all the pads and vias that looked corroded. Some of them are very resistant to reflowing or new solder but most are alright. I tested all the traces that are visibly corroded and without looking at a schematic they are all intact in so far as they are still connected to something. The only change that I have in the outcome is that the yellow screen sometimes turns to Atari green and stays constant.
The power supply has 5V, 12V and -12V. Does it need all those voltages to start?

[rubber_jonnie]

In the area that says 'Data Path' I had bad vias, it's worth getting a schematic for your board and buzzing out from top to bottom as well as point to point.

Be aware that if the solder pads, which are probably vias, have corrosion then de-soldering/re-soldering may be difficult due to the solder composition changing with the battery leakage.

You'll need to be careful to avoid putting too much heat into the area and damaging the traces and vias.

[Maximilian]

I would suggest PCBExplorer, but this is a rev.3, and it only has a rev.8 board.

Corrosion is probably the issue, you may need to use a small drill to clean the vias and resolder them with flux.

With a yellow screen, I would indeed look at the Buster/data path area.

It takes a lot of time before the kickstart screen is shown if the floppy isn't connected, so please check that.

https://retrocomputerverzamelaar.nl/com ... -problems/

[russellnash]

Yes, you are right, Jonnie, they are vias, I will test them from top to bottom. I did find a trace left of the Agnus that when I hold it up against the light it looks like it is broken through but it tests as still connected.
Thank you for that website link with the table, Maximilian, I now know that the 12V and -12V are important.
I am assuming the problem is bad connections from the corrosion and not that something suddenly broke. We will see.

[dml]

From what I can remember, the Amiga boot screen colours go something like this:

black-grey-lightgrey-white = booting normally at least as far as trying to start workbench

green = RAM fault or mis-configuration (I think it can also mean the RAM expansion is missing/unplugged or damaged, if the board is jumper-configured for extra chipram)

yellow = CPU or system related fault

There are some other colours for different things, peripherals etc. The most common confusing mistake though is unplugging the RAM expansion to investigate a problem and creating a new problem because the mainboard is configured to expect the card and won't boot without it.