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-   -   Trying to save an A4k, what did I overlook? (http://eab.abime.net/showthread.php?t=99450)

jonars 31 October 2019 19:54

Trying to save an A4k, what did I overlook?
 
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Hello!

I'm trying to save my A4K Rev B! It shows errors while reading fast Ram in DiagROM at least and does not boot Kickstart (black screen after a few seconds, then reboot loop). Continuity is given in RTC / Battery / RAM Socket area. No Expansions.

What I swapped with another A4K and is known good:
CPU Card
Chip Ram
Fast Ram
Buster
CIA A + B
LISA
ALICE
BRIDGETTE
ROM HI + LO
RAMSEY

Due to battery damage I replaced (although old parts still working):
U891
U178
U177
U976
U975

It had a light to moderate Battery damage but only three traces needed to be fixed.

It is completely recapped.

The PSU is fine.

U711 and U701 which are sometimes responsible for fails also SEEM to communicate in the correct way.

In the scope, some data Lines look strange (see screenshot attached).

With regular 3.1 Roms, reset line stays high, but the System seems to reset anyway and Power LED also shows a reboot loop, 7x blink, a few seconds black screen, reboot.

DiagRom is loading fine and shows only errors in FastRam.

I booted so many times, each time differently with slightly heating up or cooling down every chip on the board to find the bad chip. It did not give me any hints.

What signals can I trace / measure to find the culprit?

TIA and best regards
Jonars


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