MindWalker
Experienced Member
Hi.
I bought a non-working Commodore PC-1, told to be untested due to a missing power supply. It wasn't too expensive and I was hoping for just a simple power supply -remake (there are several write-ups of this as the orignal PSU seems to be rather fragile and there is a MeanWell RPT-60B which is very much a drop-in replacement).
I own another working PC-1 so I have some points of reference. Testing the new machine with the known good (recapped and tested) power supply I have power LED, but absolutely no other signs of life. There is not even a blip in the picture while powering on (either from the 9-pin display out or the RCA monochrome output, I have verified my display setup/DIP switch settings with the working motherboard) so I presume there is not even the display sync.
With the working motherboard I was able to test that all socketed ICs are good: Paradise System PPC1 and PVC2, MOS 5720, Faraday FE2010, 8088, BIOS and Character EPROMs.
For some reason half of the RAM is socketed - in my working machine the stock 512k is all soldered in, with only four sockets on the right for the expansion from 512k to 640k. At least one of the socketed RAM chips had a bent pin, one has a rusted pin and three of the chips tested bad on my Retro Chip Tester. I am not sure if all the RAM needs to be in, I have tried both ways and no difference.
I even have a PC-1 to ISA -adapter and I tested plugging in an ISA POST-card. It stays at 00 10 (I know this shouldn't really work on XTs but tested it anyway). The LEDs on the card show that the RESET line works (IRDY turns off while reset button is held), CLK and FRAME are lit all the time. Only the 8088 and the (programmable logic chips? The ones on bottom-right with white 3188xx-01 labels) get warm.
Depending on how the original power supply died, there could've been over-voltage (perhaps killing the RAMs?) but as the big chips tested good I am somewhat hopeful.
I was thinking of making a copy of Ruud's diagnostic ROM, but I am not sure if that will help, as there is no display?
I have a logic probe, and later on I can get my scope from storage so I guess I should start looking at the address and data lines (I've been watching Adrian's digital basement and I can follow his troubleshooting but I am somewhat insecure on where to start looking) etc.
All ideas are greatly appreciated
I bought a non-working Commodore PC-1, told to be untested due to a missing power supply. It wasn't too expensive and I was hoping for just a simple power supply -remake (there are several write-ups of this as the orignal PSU seems to be rather fragile and there is a MeanWell RPT-60B which is very much a drop-in replacement).
I own another working PC-1 so I have some points of reference. Testing the new machine with the known good (recapped and tested) power supply I have power LED, but absolutely no other signs of life. There is not even a blip in the picture while powering on (either from the 9-pin display out or the RCA monochrome output, I have verified my display setup/DIP switch settings with the working motherboard) so I presume there is not even the display sync.
With the working motherboard I was able to test that all socketed ICs are good: Paradise System PPC1 and PVC2, MOS 5720, Faraday FE2010, 8088, BIOS and Character EPROMs.
For some reason half of the RAM is socketed - in my working machine the stock 512k is all soldered in, with only four sockets on the right for the expansion from 512k to 640k. At least one of the socketed RAM chips had a bent pin, one has a rusted pin and three of the chips tested bad on my Retro Chip Tester. I am not sure if all the RAM needs to be in, I have tried both ways and no difference.
I even have a PC-1 to ISA -adapter and I tested plugging in an ISA POST-card. It stays at 00 10 (I know this shouldn't really work on XTs but tested it anyway). The LEDs on the card show that the RESET line works (IRDY turns off while reset button is held), CLK and FRAME are lit all the time. Only the 8088 and the (programmable logic chips? The ones on bottom-right with white 3188xx-01 labels) get warm.
Depending on how the original power supply died, there could've been over-voltage (perhaps killing the RAMs?) but as the big chips tested good I am somewhat hopeful.
I was thinking of making a copy of Ruud's diagnostic ROM, but I am not sure if that will help, as there is no display?
I have a logic probe, and later on I can get my scope from storage so I guess I should start looking at the address and data lines (I've been watching Adrian's digital basement and I can follow his troubleshooting but I am somewhat insecure on where to start looking) etc.
All ideas are greatly appreciated