Amiga 500 rev 5 blue/green screen

[AhMiggy!]

Hi,

My A500 rev 5 board is broken. When I do a cold boot I get a blue screen. But when I leave it on for a few minutes, and try to boot again, the screen turns light green. This behavior is very consistent. Depending on the screen I use it on the color is greenish cyan to light green.
Correct me if I'm wrong, but aren't RAM errors supposed to give a dark green screen?

I can already exclude the socketed chips. All test OK, including Fat Agnus and kickstart.
I did no complete recap, but I did replace the 3300 ones.

Did some further checking, it appears 68000 goes into HLT mode.

What would be some likely culprits?

If the vidiot would be fried, which behavior would I see then? Can a faulty vidiot cause the CPU to halt? I wouldn't see a colored screen to begin with I suppose?

Thanks for pointing me in the right direction!

[AhMiggy!]

Hi gertsy,
Yes, it was working before. When the problem began, I did hook it up to another power supply (A600 one), but I used it before without problems, and its voltages seem to be OK.
The board is pretty clean for its age. No apparent corrosion.
I'm not the first owner, but as far as I know it was in original state when I got it.
When it began to fail I immediately suspected Denise or Fat Agnus because at the very beginning it started as a few garbled lines in another color on the screen. That rapidly worsened, and after maybe 2-3 boots I got the blue screen.
Because Denise and Fat Agnus check out fine I began suspecting HY1 (the vidiot). But would it fail in the manner described?? Other possibilities?
I read somewhere that the HY1 sometimes fails because the 3300 caps and its accompanying resistors begin to fail (especially on Rev 5 boards). That's why I replaced de caps, and measured out said resistors, which are fine.

[AhMiggy!]

Sorry for necrobumping this old thread, but I have news concerning this particular mainboard.
I managed to fix it after all... The main problem turned out to be a cold via in the vicinity of Gary. But the blue screen I had first was a bad contact of Agnus.
I did most of my troubleshooting without keyboard. But when I recently tried it with a keyboard, I noticed the status lights were not working.
When I pushed Gary status lights did work, so something was up there. First suspecting a bad socket I replaced al my DIP sockets with dual wipe ones. Agnus socket was also replaced.
Still I had a green screen. Until I resoldered all dull looking vias around Gary. Works quite stable now. :-)
Now this thread can finally rest in peace...