A500 Rev.3 yellow screen Got diogrom working need help analising the resuts.

[Dimmy]

I try to fix an old amiga500, and got diagrom running, using extra memory in the expansion. Only serial output, when checking the ram I notice that all the ram has an error on the same spot. I am new to all this, but I like to learn. My assumption would be, that the ram is not broken, but maybe a controler? I did swap out Agnus, that did nothing.

As you can see there are the Parallel Code $fe - Test UDS/LDS line errors and the memory has a read faults (could be writing also of course) but alway on the same spot.
I switch Agnus, CPU and Garry, but that did not change anything. I looked for oxidation, did not find any. the board looks really clean.
I get into the menu via serial, because I use the expansion ram.

I also attached the memtest result and the diagrom start output

I hope that someone could help me in the right direction, on how to get closer to a fix.

Thanks all!

[Dimmy]

No, without the expansion Diagrom wil start but cant continue, because of no working chipram, This is a Rev3 board that has 512 on board and I have an original 501 expansion in there to get diagrom to work.

[Dimmy]

Thank you,

I did try to look at traces, but pcb explorer only has  A500 Rev 8A, that is completely different then the Rev3 I have here.
Maybe someone has a Kicad for Rev.3? I could not find one.

[Dimmy]

Thank you,

I tried the piggyback method, did nothing at all. tried on all 16, nothing changed in diagrom.

The I just removed U17, because of what you said and put a socket in there, and a new ram, then I got somehow other errors, so I stack tested the other rams and when I stacked U19, all the errors where gone!!

Thank you all for your Help,

I replaced the old roms with another brand: Intel p21256-80.