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Old 09 July 2018, 20:18   #1
CRP
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Location: Milano
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need help on a500 diagrom output

I have an A500 rev 6a board with black screen syndrome. When installing diagrom and looking at serial out, I get:

Code:
Amiga DiagROM V1.0 - 06-Apr-18  - By John (Chucky/The Gang) Hertell


Testing if serial loopbackadapter is installed: <> NOT DETECTED
- Parallel Code $ff - Start of ROM, CPU Seems somewhat alive
    Checking status of mousebuttons for different startups: 
            
    Set all Interrupt enablebits (INTENA $dff09a) to Disabled: Done
    Set all Interrupt requestbits (INTREQ $dff09c) to Disabled: Done
    Set all DMA enablebits (DMACON $dff096) to Disabled: Done

Testing if OVL is working: OK
- Parallel Code $fe - Test UDS/LDS line
  - Test of writing word $FFFF to $400 OK
  - Test of writing word $00FF to $400 FAILED
  - Test of writing word $FF00 to $400 OK
  - Test of writing word $0000 to $400 FAILED
  - Test of writing byte (even) $ff to $400 OK
  - Test of writing byte (odd) $ff to $401 OK
- Parallel Code $fd - Start of chipmemdetection

Addr $00000400  Write: $AAAAAAAA  Read: $FAAAFAAA  FAILED
....
(all FAILED)
....
Addr $001F8400  Write: $00000000  Read: $F000F000  FAILED

NO Chipmem detected
- Parallel Code $fc - Start of motherboard fastmemdetection
- Parallel Code $fb - Memorydetection done
- Parallel Code $80 - NO Chipmem detected
- NO MEMORY FOUND - HALTING SYSTEM
So given the above, should I replace ram chips or the logic glue chips?

thanks!
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Old 17 May 2019, 14:31   #2
apolkosnik
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Hi, I'm curious if you managed to fix this, and what seemed to be the problem? I recently ran into a very similar issue, and so far, I've replaced 244s and 373s, and it looks like the RAM chips are the next :-)
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Old 17 May 2019, 14:36   #3
CRP
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I moved over to a different unit which was easier to fix. But from the experience I cumulated since then, the issue is 99% with RAM chips. I guess this should be checkable with the piggybacking method...
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Old 19 May 2019, 09:55   #4
Mark sealey
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very intresting.....what was the ON SCREEN error....green screen...?
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Old 28 May 2019, 09:47   #5
apolkosnik
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It was a green screen. But since it was a PAL A500, and I have NTSC modulator, I was seeing a rainbow. I did the piggybacking trick and it booted.
On 6A it was the first chip from the left that was bad IIRC... When you look at the r/w test.
Write: $AAAAAAAA Read: $FAAAFAAA FAILED

Last edited by apolkosnik; 28 May 2019 at 09:54. Reason: Gigantic font
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Old 28 May 2019, 09:55   #6
Mark sealey
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Nice one...I have a rev 6a with the green screen...thought about the piggybacking method.
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