Search found 16 matches

by gregctaylor
Sun Jul 08, 2018 5:02 pm
Forum: Hardware
Topic: Still faulty 80K
Replies: 7
Views: 106

Re: Still faulty 80K

Latest gripping update!! I began by checking pin 6 of the Z80, NOT_CLK, at which the scope should have shown a 2MHz clock. I did get something at around 50Hz (bit of mains hum I think) with very low voltage and a very irregular shape. Pulled the Z80 to see if that was at fault. Same poor clock and, ...
by gregctaylor
Sat Jul 07, 2018 3:28 pm
Forum: Hardware
Topic: Still faulty 80K
Replies: 7
Views: 106

Re: Still faulty 80K

Good idea to check the Z80. I have spares as well which are for a different project but easily purloined.
by gregctaylor
Sat Jul 07, 2018 1:09 pm
Forum: Hardware
Topic: Still faulty 80K
Replies: 7
Views: 106

Re: Still faulty 80K

Thanks for the ideas. No M-ROM was not tested but my original shows exactly the same pattern so don't think it is that. Tried SG but no sound, nor out of my fully working 80A either. Perhaps I am doing it wrong? Is it SG then [Return] or just SG? I shall try the schematic and also check out the actu...
by gregctaylor
Fri Jul 06, 2018 2:33 pm
Forum: Hardware
Topic: Still faulty 80K
Replies: 7
Views: 106

Still faulty 80K

After much work and testing, it is not main RAM, I have swapped for new VRAM, swapped M-ROM and CG-ROM. Same error all the time. Have had a good look at the screen and the output is: code 10100011b (I think) then a space then either code 1100011b or 11100011b then a space then code 10100011b and so ...
by gregctaylor
Sat Jun 23, 2018 4:08 pm
Forum: Hardware
Topic: Fixed Sharp but not yet!
Replies: 5
Views: 320

Re: Fixed Sharp but not yet!

Just got back off holiday to some new VRAM chips. Have socketed the board and replaced and ...... (builds up tension ......)
.
.
.
no change . *?!!!****???!!!

The next option must be the boot ROM (EPROM?) but I don't have an EPROM blower so a bit stuck. Anyone any ideas or can help me out?

Greg
by gregctaylor
Sun Jun 17, 2018 5:34 pm
Forum: Emulation
Topic: idea: custom keyboard for MZ emulation
Replies: 7
Views: 766

Re: idea: custom keyboard for MZ emulation

An easy solution is to buy a really cheap USB keyboard, a compact one can look even better. Then print keytops, you can sometimes find images which you can scale up and print. I have found the easiest way to do this is to brush paint a little lacquer on each key, stick the paper keytop to the sticky...
by gregctaylor
Tue Jun 12, 2018 3:29 pm
Forum: Hardware
Topic: MZ-80B Power Supply Repair
Replies: 12
Views: 487

Re: MZ-80B Power Supply Repair

I unplugged all the main RAM than placed the III bank chips into bank I with no change. Unless a lot of the RAM is faulty (which must be extremely unlikely) then it must be something else. Shame the VRAM is not socketed as I could have tried that. I don't think it is the VRAM though as the screen is...
by gregctaylor
Tue Jun 12, 2018 8:58 am
Forum: Hardware
Topic: MZ-80B Power Supply Repair
Replies: 12
Views: 487

Re: MZ-80B Power Supply Repair

Just noticed the last part. It ws 16K in all 3 rows but now I have 16K in row I then 2 and 3 are empty to try that. No change.
by gregctaylor
Tue Jun 12, 2018 8:57 am
Forum: Hardware
Topic: MZ-80B Power Supply Repair
Replies: 12
Views: 487

Re: MZ-80B Power Supply Repair

I am beginning to wonder if it might be the monitor ROM (EPROM?) at fault. I have reduced it to a 16K version and no difference. The monitor displays a very regular display (two characters ABABABABAB... - not A and B) then nothing, no option to press C (and I have tried pressing it anyway with no re...
by gregctaylor
Mon Jun 11, 2018 9:47 pm
Forum: Hardware
Topic: MZ-80B Power Supply Repair
Replies: 12
Views: 487

Re: MZ-80B Power Supply Repair

Thanks for that. It explains things perfectly. Great to see the 80B working again. I now have the 80A PSU apart to change the same smoothing capacitors. The K continues to be a problem. I have reduced it back to a 16K machine and still no luck. It seems to be writing a pattern to all the RAM then, I...