Some progress - sort of ...
I managed to borrow a BBC model B from the very kind Kirk Jackson who helps keep the NZ Vintage Computing Group alive. The Z80 copro seems fine with his machine. I didn't boot CP/M as his Beeb has a Watford electronics DDNS and some funky WD1770 controller board that didn't get on with my Cumana disk drives, but it was completely stable at the Z80 monitor prompt, (As an aside, how does the DUMP command work with the Z80 monitor? I tried "dump 0100 0110", but got nothing. Had to hit escape to get the prompt back).
So the problem is with my Beeb. I also discovered through this exercise that the ROM sockets are in such a poor state that just moving the machine can cause it to become unstable - requiring another round of pin bending and contact cleaning to get it stable again. It's weird because the ROMs aren't loose in the sockets, I have to use my posh Jonard chip extractor to get them out.
I have tried swapping out the CPU, both 6522 VIAs, the 74LS245 transceiver and the video ULA with the chips from my dead Beeb - all to no avail. Also running the Beeb without the 8271 controller didn't seem to help. I have re-flowed all the joints on the IC sockets that look like they have been hand soldered. I've also checked that there is no voltage drop on the Beeb's 5v line when I connect the copro.
So my plan of action is to attack the sockets with something sharp to expose new metal on the contacts and to try and make sure they are not pushed out of shape. If that doesn't work I'll start replacing the sockets. Any advice on a more methodical approach would be greatly appreciated. I have nabbed my son's oscilloscope, so I can get a bit more sophisticated than the old multimeter.
Oh, and I missed this ...
Cheers,
Ian.
I managed to borrow a BBC model B from the very kind Kirk Jackson who helps keep the NZ Vintage Computing Group alive. The Z80 copro seems fine with his machine. I didn't boot CP/M as his Beeb has a Watford electronics DDNS and some funky WD1770 controller board that didn't get on with my Cumana disk drives, but it was completely stable at the Z80 monitor prompt, (As an aside, how does the DUMP command work with the Z80 monitor? I tried "dump 0100 0110", but got nothing. Had to hit escape to get the prompt back).
So the problem is with my Beeb. I also discovered through this exercise that the ROM sockets are in such a poor state that just moving the machine can cause it to become unstable - requiring another round of pin bending and contact cleaning to get it stable again. It's weird because the ROMs aren't loose in the sockets, I have to use my posh Jonard chip extractor to get them out.
I have tried swapping out the CPU, both 6522 VIAs, the 74LS245 transceiver and the video ULA with the chips from my dead Beeb - all to no avail. Also running the Beeb without the 8271 controller didn't seem to help. I have re-flowed all the joints on the IC sockets that look like they have been hand soldered. I've also checked that there is no voltage drop on the Beeb's 5v line when I connect the copro.
So my plan of action is to attack the sockets with something sharp to expose new metal on the contacts and to try and make sure they are not pushed out of shape. If that doesn't work I'll start replacing the sockets. Any advice on a more methodical approach would be greatly appreciated. I have nabbed my son's oscilloscope, so I can get a bit more sophisticated than the old multimeter.
Oh, and I missed this ...
I read the copro ROM in my Minipro EPROM programmer.Out of interest, how did you generate your ROM dump? By reading the EPROM in a programmer, or by using *SAVE?
Cheers,
Ian.
Statistics: Posted by simmo1010 — Sun Feb 11, 2024 2:46 am