A500 rev.3 green screen

[krs]

So I've had a rev.3 A500 for many years, that showed the dreaded green screen on bootup ever since I got it for free from a friend. Lately I've been wanting to fix it, so since the Agnus chips/sockets are often the fault I ordered new ones.

Today I put the new socket and chip on there, but to no avail. The green screen remains. I know it could also be the Gary or one of the CIA chips. But those I've tested in another machine where they seem to work fine. Their sockets also look decent enough.

That leaves the RAM chips itself I guess. I have RAM chips from an Atari STFM that I upgraded to 4MB that I could use in the Amiga, but before I go about replacing them I thought I'd ask about something else.

On the underside of the board, close to the monitor out port, there's a ground trace (I think) that looks like it's been severed right next to a bodge fix. There is however continuity there when measured. But I saw on the Amiga Hardware Database photo of the rev.3 board that that too has the same exact same thing (in upper right corner). So I'm wondering, is this supposed to be severed but for whatever reason mine isn't? And could that be related to the green screen issue? It does connect to one of the pins on the CIA, although the left one. Though in that case I guess it'd have never worked in the first place...

Attached a crappy pic of the trace on my board.

Any advice welcome, about this and other things relevant to the green screen.

 

[krs]

Update to this.

The cut trace is a factory fix. I've seen it on a bunch of rev 3 boards on GadgetUK's YT channel now. And obviously there will be continuity if it's ground, since ground should have continuity everywhere. Had a brain fart there hah. Still not quite sure what the purpose of that fix is however.

But regardless of that, the board I'm working on has sprung to life! After changing the bottom row of RAM chips out one by one. I was almost ready to give up actually, but after changing the last one (U23), to my surprise/relief the Amiga suddenly booted to the kickstart/insert workbench disk screen. This was after first switching out all the 74xx logic chips on the data paths without success. I put sockets in, so after it started working I tested the RAM chips I took out and two of them were faulty.

This would most likely have been a lot quicker to troubleshoot/pinpoint if I had a DiagROM, but alas I do not. It's on my purchase list however.

It's not completely out of the woods yet though, as there appears to be faulty RAM chips on the upper row as well since there is corruption in some software. But at least it's no longer a fancy paper weight. I'll likely switch out all the RAM chips to the ones from my Atari ST so they're all the same.

Really happy to get this board working. The PCB serial no is 015274 and seems to say it's from the 15th week of 87. The case serial no is 09897. So a very early A500. One of the CIA chips is from the 7th week of 86!