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SLOW MODE issue
Posted: Thu Jul 29, 2021 10:14 pm
by ekaww
I have built a similar replica of ZX80 w/ slow mode. It’s working fine but has only one issue when working in slow mode.
Both inverse and graphic caracteres are missing a line over the caracter as you can see in the Picture.
Has anyone ever seen this problem?
Re: SLOW MODE issue
Posted: Fri Jul 30, 2021 6:04 am
by Paul
I had the same issue with a (most probably different make of) ZX80 replika. In my case I forgot a jumper. It's the line counter reset thats missing. In your case it might be a bad or missing solder point?
Re: SLOW MODE issue
Posted: Fri Jul 30, 2021 5:18 pm
by ekaww
Hi Paul,
What's the line counter in your ZX80 replica? The counter of mine is 74LS393.
I have attached the slow mode schematic and I checked and re-checked several times.
Re: SLOW MODE issue
Posted: Fri Jul 30, 2021 10:05 pm
by Paul
I really don't know. Mine has been a replica made by Lee Hart many years ago. In this forum.So you should be able to find his schematic with the search function. It used "modern" parts so it wasn't very close to the original
Re: SLOW MODE issue
Posted: Fri Jul 30, 2021 11:52 pm
by 1024MAK
Pins 2 and 12 are the clear/reset pins on a 74LS393 counter. So check/test logic levels on these and the circuitry feeding them.
Can you please put your image in a zip file, then upload, so the forum software does not compress the image…
Mark