The A2000 of instability

[3VILC]

Ok, so my A2000 has started being a royal pain in the backside.
Rev4.3 board hotfixed to 4.4, 8372A Agnus configured as 1meg chip, KS2.04, A2091 SCSI controller with 2meg, plus 2 other 2meg Z2 boards.
The main issue is it has stopped booting with the A2091 RAM enabled for some reason, it will instantly crash as soon as its powered up. I've tried with my spare A2091 and that strangely does exactly the same thing. Disable the RAM (by setting the jumper to 0meg) and everything works fine, the other Zorro ram boards work fine regardless. So it has to be something on the motherboard right? But where do I start looking? The bus buffers have already been swapped for 74ALS245's (or they always were).
DiagROM crashes with "BusError" the instant you try test the A2091 RAM if the jumper is enabled.
Also possibly related but maybe not, I've tried to burn a KS3.2 rom for the machine and it will either crash during booting the hard drive or just crash randomly after a few seconds on the 'kickstart" screen if hard drive booting is disabled. But the same rom doesn't work at all in my A500 either which I can't work out why.

Any repairers able to offers some advice where to start looking/what to start looking for before I start aimlessly poking around with the scope, would be much appreciated

[SkulleateR]

Guess the A2091 will try to use the same adress space as one of the other 2meg expansion and that results in a crash

[giantclam]

Ok, so my A2000 has started being a royal pain in the backside.

Are you saying this setup was working fine, and has since developed this problem?

[3VILC]

Correct yes, all cards autoconfig and were working fine together, but the RAM on either A2091 now longer works no matter what other cards are in the system. And the ram chips have been swapped around and tested in other expansions

[giantclam]

Originally Posted by 3VILC

Correct yes, all cards autoconfig and were working fine together, but the RAM on either A2091 now longer works no matter what other cards are in the system. And the ram chips have been swapped around and tested in other expansions

M'kay... are you saying here, it fails to boot with only the A2091 in slot (all other cards removed)?

[Trapshot]

Checked the power supply?

[3VILC]

Originally Posted by giantclam

M'kay... are you saying here, it fails to boot with only the A2091 in slot (all other cards removed)?

Yup, no other cards except the A2091. Exact same behaviour, power LED low, high briefly, then blinking indicating crash. Disable 2091 RAM everything is fine.

Incidentally II fixed the Kickstart 3.x not working issue so that's totally unrelated to this bus error

[3VILC]

Originally Posted by Trapshot

Checked the power supply?

Checked PSU output, voltages all look fine