Search found 186 matches

by Tezz
Sat Mar 11, 2017 4:15 pm
Forum: Hardware
Topic: ZX81 repair and upgrade. Help! I now have a white screen output
Replies: 26
Views: 8541

Re: ZX81 repair and upgrade. Help! I now have a white screen output

I continued this afternoon, took the 0v ground wire out of the modulator can and solder tacked on an extending wire connected directly to the ground of the board where the modulator leg would be soldered. Connected the system with RAM pack to the TV, no change. The CRT TV has a black output that has...
by Tezz
Fri Mar 10, 2017 8:09 pm
Forum: Hardware
Topic: ZX81 repair and upgrade. Help! I now have a white screen output
Replies: 26
Views: 8541

Re: ZX81 repair and upgrade. Help! I now have a white screen output

Thanks, I'll try connecting the ground next. As the zx81 board was working correctly (with a dark no back porch output) before I took out the modulator and fitted the new video circuit, it can only be the new video circuit at fault. Removing the ULA and adding the socket/new ULA after that I think i...
by Tezz
Fri Mar 10, 2017 2:39 pm
Forum: Hardware
Topic: ZX81 repair and upgrade. Help! I now have a white screen output
Replies: 26
Views: 8541

Re: ZX81 repair and upgrade. Help! I now have a white screen output

Some progress this morning.. I checked with the multimeter between pin 26 of the ULA to pin 8 of the Z80 @ 200 Ohm range, display showed a higher figure quickly dropping and holding at 0.065. I cleaned the expansion connector again with IPA which did take some more grime off. connected the system an...
by Tezz
Fri Mar 10, 2017 11:46 am
Forum: Hardware
Topic: ZX81 repair and upgrade. Help! I now have a white screen output
Replies: 26
Views: 8541

Re: ZX81 repair and upgrade. Help! I now have a white screen output

Thanks Martin, I had a read through that thread. I will buy a logic probe to help diagnose these problems, that will be helpful. If the ULA turns out to be faulty, I guess any of the NOS ULA's are all sold by now? I'd rather buy a working ULA instead of pulling one from another working board which w...
by Tezz
Fri Mar 10, 2017 12:07 am
Forum: Hardware
Topic: ZX81 repair and upgrade. Help! I now have a white screen output
Replies: 26
Views: 8541

Re: ZX81 repair and upgrade. Help! I now have a white screen output

Thanks Mark :) I'll test the connections in the morning between the ULA pins and the Z80 pins with the multimeter like you suggested. I started using wire stripped from cat5 cable as jumper wire but I didn't find it easy to work with and I found the insulation melts extremely easily when soldering t...
by Tezz
Thu Mar 09, 2017 10:20 pm
Forum: Hardware
Topic: ZX81 repair and upgrade. Help! I now have a white screen output
Replies: 26
Views: 8541

ZX81 repair and upgrade. Help! I now have a white screen output

Hi to all, This is my first post here, I've recently become interested in developing for the ZX81 and thought It'd be a good break from coding first to repair, restore and upgrade a few ZX81's to keep them living on and put them back into circulation. I ended up buying eight along with a 16K RAM pac...