Crashedfiesta
Experienced Member
- Joined
- Apr 16, 2022
- Messages
- 82
(Wasn't sure if this was best here or in Technical Support!)
I recently acquired an A2000 (for free!) from a nice chap. The power supply was completely borked (outputting 6.5v on the 5v lines and 9v on everything else...) so I hooked up an ATX power supply. The battery had leaked so I had to clean that up too.
After lots of trace and pad repairs and chip swaps I have reached an impasse. Basically, using DiagROM 1.3 the thing boots but declares there is no chip memory and halts. But the weird thing is, if I deliberately disable one of the data bits by bending out the relevant pin on U106 or U104, then DiagROM does a complete test of the onboard RAM. Obviously it reports faulty bits and then halts but I can move the faulty bit around by bending out the relevant leg for each bit. As a result I'm fairly confident that there are no issues with the actual DRAM chips on the board.
But I'm really stumped as to why, when all the chips are inserted correctly, DiagROM is not seeing the memory. This is the serial output I get from DiagROM1.3 Beta:
Full text below:
Amiga DiagROM V1.3 BETA - 12-Jun-21 - By John (Chucky/The Gang) Hertell
- Parallel Code $ff - Start of ROM, CPU Seems somewhat alive
- Testing ROM Address-access
OK
Testing if serial loopbackadapter is installed: <> NOT DETECTED
Checking status of mousebuttons at power-on:
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 $AAAA to $400 OK
- Test of writing word $00AA to $400 OK
- Test of writing word $AA00 to $400 OK
- 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 $00010400 OK Number of 64K blocks found: $01
Chipmem Shadowram detected, guess there is no more chipmem, stopping here
Startaddr: $00000400 Endaddr: $0000FFFF
- Testing detected Chipmem for addresserrors
- Filling memoryarea with addressdata
- Checking block of ram that it contains the correct addressdata
CHIPMEM OK
- Checking status of mousebuttons for different startups, if still pressed
we assume not working and ignore those in the future.
Green newly pressed, Yellow pressed at startup - Startupaction taken.
Red = Pressed at both poweron and now so it is stuck and being ignored
The following special action will be taken:
NONE
- Parallel Code $fc - Trying to find some fastmem (as no chipmem found)
- Parallel Code $fb - Memorydetection done
- Parallel Code $80 - NO Chipmem detected
- NO MEMORY FOUND - HALTING SYSTEM
I have two copies of the schematics, one for the A2000 Rev4 which is a scanned pdf, and one for the (almost identical) Rev 6 which is the really nice modern reconstructed schematic. From these I have spent hours checking traces and trying to make sure there are no shorts or missing signals. I found one missing 5v line to U540 but that was it. Everything else I've repaired looks OK.
Help!!
Some pics for your entertainment.
This is the board immediately after I dismantled the case for the first time. I've since cleaned it thoroughly and replaced the MegaChip for a standard 8372A Agnus - just until I get it sorted.
Agnus needed a new socket..
Board revision 4
The keyboard (photobombed by an A1200 case). Apparently, these keyboards are quite rare. It's the one with the clicky Cherry switches.
I recently acquired an A2000 (for free!) from a nice chap. The power supply was completely borked (outputting 6.5v on the 5v lines and 9v on everything else...) so I hooked up an ATX power supply. The battery had leaked so I had to clean that up too.
After lots of trace and pad repairs and chip swaps I have reached an impasse. Basically, using DiagROM 1.3 the thing boots but declares there is no chip memory and halts. But the weird thing is, if I deliberately disable one of the data bits by bending out the relevant pin on U106 or U104, then DiagROM does a complete test of the onboard RAM. Obviously it reports faulty bits and then halts but I can move the faulty bit around by bending out the relevant leg for each bit. As a result I'm fairly confident that there are no issues with the actual DRAM chips on the board.
But I'm really stumped as to why, when all the chips are inserted correctly, DiagROM is not seeing the memory. This is the serial output I get from DiagROM1.3 Beta:
Full text below:
Amiga DiagROM V1.3 BETA - 12-Jun-21 - By John (Chucky/The Gang) Hertell
- Parallel Code $ff - Start of ROM, CPU Seems somewhat alive
- Testing ROM Address-access
OK
Testing if serial loopbackadapter is installed: <> NOT DETECTED
Checking status of mousebuttons at power-on:
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 $AAAA to $400 OK
- Test of writing word $00AA to $400 OK
- Test of writing word $AA00 to $400 OK
- 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 $00010400 OK Number of 64K blocks found: $01
Chipmem Shadowram detected, guess there is no more chipmem, stopping here
Startaddr: $00000400 Endaddr: $0000FFFF
- Testing detected Chipmem for addresserrors
- Filling memoryarea with addressdata
- Checking block of ram that it contains the correct addressdata
CHIPMEM OK
- Checking status of mousebuttons for different startups, if still pressed
we assume not working and ignore those in the future.
Green newly pressed, Yellow pressed at startup - Startupaction taken.
Red = Pressed at both poweron and now so it is stuck and being ignored
The following special action will be taken:
NONE
- Parallel Code $fc - Trying to find some fastmem (as no chipmem found)
- Parallel Code $fb - Memorydetection done
- Parallel Code $80 - NO Chipmem detected
- NO MEMORY FOUND - HALTING SYSTEM
I have two copies of the schematics, one for the A2000 Rev4 which is a scanned pdf, and one for the (almost identical) Rev 6 which is the really nice modern reconstructed schematic. From these I have spent hours checking traces and trying to make sure there are no shorts or missing signals. I found one missing 5v line to U540 but that was it. Everything else I've repaired looks OK.
Help!!
Some pics for your entertainment.
This is the board immediately after I dismantled the case for the first time. I've since cleaned it thoroughly and replaced the MegaChip for a standard 8372A Agnus - just until I get it sorted.
Agnus needed a new socket..
Board revision 4
The keyboard (photobombed by an A1200 case). Apparently, these keyboards are quite rare. It's the one with the clicky Cherry switches.
