12 June 2024, 18:03 | #1 |
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A1200 green screen - seemingly quite random chip mem issues with diagrom, any
I've got an A1200 with green screen, and I'm struggling to diagnose the issue.
Sadly I fear it's not as simple as a broken trace etc, or even bad RAM chip(s), but I'm still hopeful! I inherited this machine and the first time I turned it on, it got to workbench disk screen, but then started to alternate with green screen, and now always green screen (with KS3.0 and 3.2.2). Likely leaky cap damage you say? Well... the board was in immaculate condition with no obvious signs of electrolyte damage. I have de-capped (not yet recapped) and there was some leakage immediately below a couple of the caps which is cleaned up but nothing that seemed too bad. I'm not ruling it out, but given the diagrom output it's hard to understand what might be going on. Diagrom: I get random results from the chipram testing. Some addresses fail, Bit 10 is always "1" on read - this could indicate a problem with a data line or RAM chip (I think this is D10, but correct me if I'm wrong?), and it detects random amounts of "working" chip memory. Which then always fails later in working memory test, anyway. To me this looks like some kind of instability/inconsistency with the ram access/bus, but not sure where to start? It's a REV 2B, so I understand it uses each chip to store 8 bits per 32 bit address. I've checked VCC to the RAM chips I've checked continuity on a bunch of the data lines and also CAS/RES etc, but all seem to be fine. Alice is getting warm but not mental I've checked the PSU voltages and they're rock solid, and the same PSU runs an A1200/pistorm with no issues. Next step is to scope out some signals I guess (which requires me to get my scope back from a friend!), but I wondered if anyone had experience with similar issues to point me in the right direction? I have some replacement ram chips but I'm loath to do SMD replacement until I'm a bit clearer on whether they're the issue or this indicates a custom issue (maybe alice or budgie?) or something completely separate. Thanks in advance! Example diagrom output: Code:
Testing if OVL is working: OK - Parallel Code $fe - Test UDS/LDS line - Test of writing word $AAAA to $400 FAILED - Test of writing word $00AA to $400 FAILED - Test of writing word $AA00 to $400 FAILED - Test of writing word $0000 to $400 OK - Test of writing byte (even) $AA to $400 OK - Test of writing byte (odd) $AA to $401 OK - Parallel Code $fd - Start of chipmemdetection Addr $00000400 Write: $FFFFFFFF 11111111111111111111111111111111 Read: $AAAA0400 10101010101010100000010000000000 FAILED Write: $AAAAAAAA 10101010101010101010101010101010 Read: $AAAA0400 10101010101010100000010000000000 FAILED Write: $55555555 01010101010101010101010101010101 Read: $AAAA0400 10101010101010100000010000000000 FAILED Write: $F0F0F0F0 11110000111100001111000011110000 Read: $AAAA0400 10101010101010100000010000000000 FAILED Write: $0F0F0F0F 00001111000011110000111100001111 Read: $AAAA0400 10101010101010100000010000000000 FAILED Write: $0F0FF0F0 00001111000011111111000011110000 Read: $AAAA0400 10101010101010100000010000000000 FAILED Write: $00000000 00000000000000000000000000000000 Read: $AAAA0400 10101010101010100000010000000000 FAILED Addr $00010400 Write: $FFFFFFFF 11111111111111111111111111111111 Read: $14617741 00010100011000010111011101000001 FAILED Write: $0F0F0F0F 00001111000011110000111100001111 Read: $FFFFFFFF 11111111111111111111111111111111 FAILED Addr $00020400 Write: $FFFFFFFF 11111111111111111111111111111111 Read: $14617745 00010100011000010111011101000101 FAILED Code:
Addr $00160400 OK Number of 64K blocks found: $01 Startaddr: $00150400 Endaddr: $0015FFFF - Testing detected Chipmem for addresserrors - Filling memoryarea with addressdata - Checking block of ram that it contains the correct addressdata - Addresserror at: 00150404 00000000000101010000010000000100 A2EAA2AA - Addresserror at: 0015040C 00000000000101010000010000001100 2B15000C - Addresserror at: 00150424 00000000000101010000010000100100 00150424 - Addresserror at: 0015042C 00000000000101010000010000101100 3A15002C - Addresserror at: 00150444 00000000000101010000010001000100 00150444 |
15 June 2024, 18:59 | #2 |
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Anyone able to help intepret/debug possible causes of this type of diagram chipram test output?
Specifically - a mix of seemingly random wrong bits across whole address, plus a bit permanently returning “1” (in an rev 2b, which I understand uses all 4 chips for each address) I’m thinking of replacing the RAM chips (perhaps starting with 2nd most LSB chip which I think is second from bottom). But any other pointers gratefully received. Thanks |
15 June 2024, 19:00 | #3 |
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Also note the errors seem to be occurring randomly - each boot gives different results.
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