billdeg
Technician
(this is a copy of a post I sent to the N* Yahoo Group)
There's an old thread about this project, but I am starting a new one.
1) Not getting 5V to the A drive (less than 2V). Traced the problem to the 7805 inside heatsink, 6030B, the front-most 7805. I replaced the 7805 and now I get the correct voltage to everything.
2) I checked every card, they all seem to be getting the correct voltages (12 or 5)
ZPB processor (also have a ZPB-2)
MDS-AD3 (also have a MDS)
IMS 4mhz 16K RAM set for top memory (I believe - checking to confirm)
N* 16K RAM bd (8000-Bfff)
n* 32K RAM bd (0-7fff)
3) I installed an in-circuit z80 emulator to check the memory (read / write test) - no errors through 7FFF. I can't write to anything above that, but the RAM is there, unsure why but I assume that this is part of an initial lockdown of RAM by design, as part of the bootstrap process (I have to confirm this). It's possible also that the emulator is not allowing the ROM to finish what it needs to do. Not worried at this point. I checked location E800 and what appears to be bootstrap code is located in this location (which is where the manual says it should be). I don't at the moment have a copy of the bootstrap code, but I assume I can find this on the web to confirm it's loading into memory. Looking for that now.
4) When I power on the machine, both drives spin but neither engage the boot disk. After maybe 20 seconds the drives stop spinning. I verified that the drive dip switches were correct from when the system worked. I also tried other similar drives (using Tandon 100-2A's). It's possible that I have the wrong settings,. but this is what worked before:
A DRIVE: Tandon 100-2A jumpering TP11's 2nd (facing from the front) and inserting a T-RES terminator in TP7
B DRIVE: MPI model 52 with G jumpers on: 2-5-7, terminator installed (not needed).
I must be getting close. I will let you know if I make more progress. .
There's an old thread about this project, but I am starting a new one.
1) Not getting 5V to the A drive (less than 2V). Traced the problem to the 7805 inside heatsink, 6030B, the front-most 7805. I replaced the 7805 and now I get the correct voltage to everything.
2) I checked every card, they all seem to be getting the correct voltages (12 or 5)
ZPB processor (also have a ZPB-2)
MDS-AD3 (also have a MDS)
IMS 4mhz 16K RAM set for top memory (I believe - checking to confirm)
N* 16K RAM bd (8000-Bfff)
n* 32K RAM bd (0-7fff)
3) I installed an in-circuit z80 emulator to check the memory (read / write test) - no errors through 7FFF. I can't write to anything above that, but the RAM is there, unsure why but I assume that this is part of an initial lockdown of RAM by design, as part of the bootstrap process (I have to confirm this). It's possible also that the emulator is not allowing the ROM to finish what it needs to do. Not worried at this point. I checked location E800 and what appears to be bootstrap code is located in this location (which is where the manual says it should be). I don't at the moment have a copy of the bootstrap code, but I assume I can find this on the web to confirm it's loading into memory. Looking for that now.
4) When I power on the machine, both drives spin but neither engage the boot disk. After maybe 20 seconds the drives stop spinning. I verified that the drive dip switches were correct from when the system worked. I also tried other similar drives (using Tandon 100-2A's). It's possible that I have the wrong settings,. but this is what worked before:
A DRIVE: Tandon 100-2A jumpering TP11's 2nd (facing from the front) and inserting a T-RES terminator in TP7
B DRIVE: MPI model 52 with G jumpers on: 2-5-7, terminator installed (not needed).
I must be getting close. I will let you know if I make more progress. .
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