Search found 51 matches
- Fri Jan 22, 2021 6:18 pm
- Forum: Hardware
- Topic: ZX80 machine that shows a cursor but no text FIXED! :)
- Replies: 18
- Views: 5359
Re: ZX80 machine that shows a cursor but no text
OK! some success :) I was just about to give up for the day, when I thought "I've socketed IC9, so why don't I just try another 74LS165N?" and WOW! there's a 'K' in the cursor :D I pressed 'O' and up pops the word "PRINT" :D , but as I left the machine for a few seconds, it started typing random let...
- Fri Jan 22, 2021 1:38 pm
- Forum: Hardware
- Topic: ZX80 machine that shows a cursor but no text FIXED! :)
- Replies: 18
- Views: 5359
Re: ZX80 machine that shows a cursor but no text
Which pin on IC9 would be the shift register, pin 1? I've compared all the pins on IC9 to a fully working ZX80, the only difference I can see, is 3.8V on pin 1 on the faulty machine, where it is 4.2V on the working one. Pin 1 3.8V on faulty 4.2V on working (that was measured on my oscilloscope, with...
- Thu Jan 21, 2021 12:57 pm
- Forum: Hardware
- Topic: ZX80 machine that shows a cursor but no text FIXED! :)
- Replies: 18
- Views: 5359
Re: ZX80 machine that shows a cursor but no text
A14 looks like data
A15 looks like data
MREQ looks like a pulse
- Thu Jan 21, 2021 11:59 am
- Forum: Hardware
- Topic: ZX80 machine that shows a cursor but no text FIXED! :)
- Replies: 18
- Views: 5359
Re: ZX80 machine that shows a cursor but no text
@1024MAK
"I would be very surprised if a ZX80 consumes 3A or 4A! More likely to be 0.3A or 0.4A"
Of course, just me being stupid
I will check what you have suggested, and I very much appreciate the help.
I assume the Z80 is running, because I get a blank cursor which moves when I press keys.
"I would be very surprised if a ZX80 consumes 3A or 4A! More likely to be 0.3A or 0.4A"
Of course, just me being stupid

I will check what you have suggested, and I very much appreciate the help.
I assume the Z80 is running, because I get a blank cursor which moves when I press keys.
- Wed Jan 20, 2021 6:24 pm
- Forum: Hardware
- Topic: ZX80 machine that shows a cursor but no text FIXED! :)
- Replies: 18
- Views: 5359
Re: ZX80 machine that shows a cursor but no text
Yes, Thanks Moggy. As for testing the pins on IC9, I've compered the same pins on a working ZX80 and found them to look similar but pins 1 and 7 are about 0.5V higher. Thinking that I might have a short somewhere I removed the PSU and attached my bench supply at 9V, to find that the working ZX80 dra...
- Wed Jan 20, 2021 5:45 pm
- Forum: Hardware
- Topic: ZX80 machine that shows a cursor but no text FIXED! :)
- Replies: 18
- Views: 5359
Re: ZX80 machine that shows a cursor but no text
It is the small hole type, maybe I'll try swapping it.
I assume the top traces on the board will be connected by vias through the board, but maybe one has gone bad.
I assume the top traces on the board will be connected by vias through the board, but maybe one has gone bad.
- Wed Jan 20, 2021 5:05 pm
- Forum: Hardware
- Topic: ZX80 machine that shows a cursor but no text FIXED! :)
- Replies: 18
- Views: 5359
Re: ZX80 machine that shows a cursor but no text
I've tested both the ROM socket and the CPU socket. I tested them with the chips in place, making sure there is a circuit from the chips leg to the underside of the board.
- Wed Jan 20, 2021 4:52 pm
- Forum: Hardware
- Topic: ZX80 machine that shows a cursor but no text FIXED! :)
- Replies: 18
- Views: 5359
Re: ZX80 machine that shows a cursor but no text
Thanks again for the replies. I've been busy trying to fix other things, but now I'm back to these ZX80's :) I only have a Hantek 6022BE USB oscilloscope and Hscope software (Which I might not even be using properly), but this is what I've found. IC9 Pin 1, 3.7V flat-ish looking. IC9 Pin 2, 1.5V loo...
- Tue Jan 12, 2021 8:20 pm
- Forum: Hardware
- Topic: ZX80 machine that shows a cursor but no text FIXED! :)
- Replies: 18
- Views: 5359
Re: ZX80 machine that shows a cursor but no text
Just to add, I removed IC9 and tested it, it works fine. I've installed a new IC and it's the same.
- Tue Jan 12, 2021 6:05 pm
- Forum: Hardware
- Topic: ZX80 machine that shows a cursor but no text FIXED! :)
- Replies: 18
- Views: 5359
Re: ZX80 machine that shows a cursor but no text
Thanks for the reply.
I have around 6.4MHz clk on pin 2 and it looks like some data on D7.
I have around 6.4MHz clk on pin 2 and it looks like some data on D7.