Sharp MZ

Moving forward slowly. Replacing the 7404 and the tuning capacitor means I now have a good clock on the Z80. Still no change to the display though. I will swap out the Z80 a second time (in case the lack of clock was hiding the fact the Z80 had also failed) but, if not, will then attach the video ci...

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, ...

Good idea to check the Z80. I have spares as well which are for a different project but easily purloined.

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...

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 ...

Just got back off holiday to some new VRAM chips. Have socketed the board and replaced and ...... (builds up tension ......)
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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

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...

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...

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.

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...