Data General Nova

Firstly a disclaimer. I know very little about Data Ganeral machines. The only one I own is a Nova 1200 which somebody stole the frontpanel PCB from. S've never made a replacement, I've never worked on it. Maybe some day, On the other hand, I have done a lot of (component level [1] troubleshooting and repairs on machiens of simialr vintage. So I can make a few genral comments. [1] Is there any other kind ? In anotyehr message you compare repairing this machine to doing VT100. And you say that the Nova is a lot harder. I would say it's differnt, not necessarily harder. Yes, there are a lot of compoents, but they are all documented. Unliek the VT100 where you don't know the ROM contents (fidning a single-bit error i nthe ROM could prove 'intresting'), and there are undocuemtned transofers in the PSU and monitor PCB sections. But anyway... IIRC you have a stuck bit somewhere in the data path (around the ALU, possibly?). It is by no means uncommongf for the ALU to be used to update the program counter on such machines (certainly DEC and HP did this) and thus a problem with the data path section can easily prevent programs form running. I would attack this problem first. As an aside, one thing I hae learnt is that if you find a problem, correct it. Even if it _appears_ to make things worse, the machine can't work properly if something is defective. So fix all you find. [...] My experiense is that PSU problems can cause seemingly unrelated faults. Like the time my PDP11/45 would run fine for about 30 minutes nad then fail in an odd way. Turned out the +5V line to part fo the CPU was sitting at 4.4V. I would check all power supply outputs _on load) for votlage and ripple (use a 'scope on them). Again, if anything seems wrong, correct it. It may not help, but at least it will elimnate this as a possible cause. -tony