UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Gemini 80-Bus System

john_newcombe · 11th Jan 2020, 10:55 am

With the Christmas holiday now well and truly behind me, it is time to look into sorting the Gemini MFB. Alas, once again I am needing your help and expertise as the system is not working.

The unit consists of a GM813, SVC, GM849 (factory modified for Multi-Format), Xebec/HD and all floppies except 3inch.

Basic checks of PSU voltages, cabling, sockets, card reseating/repositioning etc. have been undertaken with no change in symptoms. I have now reduced the system to two cards, the GM813 and the SVC.

The SVC has been tested successfully in my rack system by replacing the rack's IVC card. So... looking at the GM813 I see no activity on the Address or Data bus.

Investigations so far show that the clock signal when viewed at the CPU looks good and that the system is not held at reset nor in a halted state.

I have swapped the CPU between this and the rack system to no effect, i.e. the rack system works with the MFB CPU, the issues with the MFB system are the same. I also dumped the Simon ROM successfully and popped RP/M 2.1 into the GM813 for good measure, alas, no change in symptoms.

It would be awesome to get this system back to good health, if anyone has any thoughts of how to take this forward, I would really appreciate it.

11th Jan 2020, 10:55 am	#299
john_newcombe Hexode Join Date: Apr 2019 Location: Skipton, North Yorkshire, UK. Posts: 252	Re: Gemini 80-Bus System With the Christmas holiday now well and truly behind me, it is time to look into sorting the Gemini MFB. Alas, once again I am needing your help and expertise as the system is not working. The unit consists of a GM813, SVC, GM849 (factory modified for Multi-Format), Xebec/HD and all floppies except 3inch. Basic checks of PSU voltages, cabling, sockets, card reseating/repositioning etc. have been undertaken with no change in symptoms. I have now reduced the system to two cards, the GM813 and the SVC. The SVC has been tested successfully in my rack system by replacing the rack's IVC card. So... looking at the GM813 I see no activity on the Address or Data bus. Investigations so far show that the clock signal when viewed at the CPU looks good and that the system is not held at reset nor in a halted state. I have swapped the CPU between this and the rack system to no effect, i.e. the rack system works with the MFB CPU, the issues with the MFB system are the same. I also dumped the Simon ROM successfully and popped RP/M 2.1 into the GM813 for good measure, alas, no change in symptoms. It would be awesome to get this system back to good health, if anyone has any thoughts of how to take this forward, I would really appreciate it.