Attempt to resurrect Rev 3 A500

[StLovell]

Hi everyone. I'm a newbie on here - not new to Amigas - but looking for assistance with this machine if poss.



I have an early revision 3 A500 (mobo S/N 0000361) that's being troublesome. I acquired it a few years ago for my collection but haven't tried to get it going until now.
Initially it just produced a green screen with the power light blinking 10 short/1 long (failed RAM at first address).
I tested and reseated all the custom chips at this point and checked for any obvious damage to traces. None of the RAM chips were getting hot.
In the end I settled on it being an issue with the system clock and got it to boot by adjusting the trimmer capacitor which seems to be unique to these boards. Sadly that lasted for only around 20 minutes and then it died again.
Next I added a 501 expansion in the trapdoor, this got it to go as far as the light grey stage of boot up (last part = OK software) but it just either hangs there or cycles through reboots with 7 short/1 long (I think) blinking out on the power light (can't find any info on this).
Now though, if I remove or disable the RAM expansion, it doesn't go back to the green screen. Instead I get a yellow screen with the same 10/1 code on the power light.
I've been round the board with a multimeter and all the voltages are spot on. There are also no bulging or leaking capacitors.
My next intention is to try piggybacking known good RAM chips over the fixed ones in turn to see where that gets me.

Has anyone got any ideas, or know what common fail points are with this board? I know the rev 3 boards are buggy at best but I'm pretty sure I should be able to get more out of it than I am.

[StLovell]

Well I had this running for a while yesterday, having found and bridged a bad RAM chip using parts from a butchered A501. Unfortunately, after a short while the bridged chip died and the green screen was back again.
I now have another chip soldered over the bad one and will proceed to replace the capacitors in this area. Hopefully it'll then live a little longer.

I also found that someone had attempted to repair the keyboard in the past and made a complete hash of it. I'd been wondering why the power/drive light poked out the top of the case a long way, and why the drive light didn't work at all.
Happily these are now sitting at the proper height and working. All I need for it is 1 key cap which is missing (K). The caps on these early keyboards are unique and rare.