About half a year ago I started repairing a badly battery damaged A2000 which had some memory issues. After a looong time of letting the project settle I finally got somewhere in the repair. The problem was a almost rotted trace for _UDS, just outside the area which I cleaned. It was still good enough to sometimes work but bad enough to not do so reliably. Also broken was the Even CIA and probably some ram chips (I just replaced all because I started being frustrated lol). I Fixed those issues and now Diagrom boots up without any memory errors and the memory test and the CIA tests succeed.

Now however I'm faced with another Problem:
Although diagrom boots I can only use it with the serial terminal. Nothing is ever displayed on the screen except for some flashing green bars at startup and then some random colors as the rom is "forcing stuff to run in fastmem if avaible".
Running any graphic tests also yields nothing but a slightly differently color-filled screen, except in "test raster" where I get some purple-green lines across the screen. I've verified that the color value output from Denise is actually what the display shows (so eliminated the Vidiot as a possible fault) and tested the monitor with my working a500.

And another issue I noticed is that the audio tests are non functional. They do play a tone but it is interrupted (sounds just like morse code). No idea if the two faults are related though.

I'm once again out of ideas for what to try as I've swapped around All chips between another A500 and the A2000 and none make any kind of a difference. Has anybody maybe seen this issue before?

Hi,

Simple answer is “Yes”, have had this even on a Rev 1D1 mainboard. The answer maybe that the top RF shielding is needed. Or the drive motor has become too noisy on the drive.
Is the drive by chance a Panasonic one?

Actually yes it is a newer panasonic drive.  This is an Escom Amiga made in France.  I've suspected it could actually be the floppy drive drawing too much current on motor start.  Its not a shielding problem, its the 5V rail dipping and the monitor loses sync, I can see it on my scope.  It happens even with all shielding installed.  I've tried different power supplies so its not the supply.  I've tried a different video cable.  This is a bare bones mainboard no accelerator.

oops replied to myself

A friend mentioned this to me today, and the full article is available online.

https://www.theguardian.com/games/2024/apr/26/my-undying-love-for-the-painfully-uncool-amiga

Yes, see my response in this separate thread:
https://forum.amiga.org/index.php?topic=75191.0

I doubt if it was actually a case of "CBM ordering the wrong memory type" as suggested in this thread; more likely there was a supply or cost issue with the usual DRAMs qualified for the design, and this was a short term solution to allow use of an alternative DRAM part.