My first ZX80.

[Muttley Black]

Hello Moggy an thanks for your reply!

I don't have an old crt tv at home to test it. Looking forward to buy one, to be able to test this beauty!

And for sure i post every steps here.

[1024MAK]

Well done, that looks in very good visual condition. Certainly better than the one I got!

Can’t really help with fault finding at the moment, as I’m no a train.

Will try to help when I can find some spare time

Mark

[Muttley Black]

I just got an roadstar tvm-1003 mini TV that can play both UHF & VHF. The best signal I have is in VHF channel. Hitting any key on keyboard make the screen a bit black for a second.

Here is the screen:

[bola_dor]

I just got an roadstar tvm-1003 mini TV that can play both UHF & VHF. The best signal I have is in VHF channel. Hitting any key on keyboard make the screen a bit black for a second.

Here is the screen:

Nice ZX80.. looks like you have sync but no video. As far as I ve learned video generation is different from ZX81 an signas has sync separated from video reaching the modulator..
I have a new ZX80 since yesterday an couldn't conect to a screen yet .. my modern LCD didn't like the signal yet and I'll have to open (*) to test any kind of non destructive adaptor
This videos have lots of information
https://youtu.be/qqUxXrh_xgM
https://youtu.be/LvMulUCxi_Y

One thing I've noticed is that he diagnosed IC21 as missing power in both of the ZX80.. IC21 is a 74LS93 and VCC and GND are pins 5 and 10 and not in the corners.. I hope he saw this and didn't mistake that..
(I wonder if the guy in the video is at this forum)

(*) just to better my own english, do you refer to an old computer like this like "it" or "her"? How does it sound naming it/her as "machine"?
Regards

[1024MAK]

The ZX81 has additional hardware so that it can compute and display (known as SLOW mode on the ZX81). On a ZX81, FAST mode is equivalent to the display system on a ZX80. That is when processing a program, video output is no longer generated (so the screen blanks) until either the program waits for user input (e.g. INPUT command) or the program ends and returns to the BASIC prompt.

The display will also flicker (to blank and then return) whenever you press a key on the keypad (keyboard).

The ZX80 does not generate the ‘back porch’ part of the video signal, so just like a ZX81 with either of the first two ULA versions, it’s tricky finding a modern TV that works well with it.

Hitting any key on keyboard make the screen a bit black for a second.

That would be the screen flickering to blank as I described above. This is a good sign. If it’s working correctly, you should have a inverted K in the bottom left corner of the screen. But as you haven’t, it looks like there may be a fault with the video character generation circuitry.

Do you have an audio amplifier? If yes, connect it to the MIC socket using a mono 3.5mm jack plug (U.K. name, known elsewhere by different names...) and then blind type [ E ] and [New Line] to see if it can SAVE to tape (the ZX80 does not use file/program names). There is no need to actually enter a program, the ZX80 will happily save a program with no lines of code! If it’s working you should hear the saving noise...

In English when referring to an object, mostly we use ‘it’, but for favourite things that are loved, sometimes ‘her’ or ‘she’ is used. Especially for cars Some people even name their loved items.

Mark

[Muttley Black]

Do you have an audio amplifier? If yes, connect it to the MIC socket using a mono 3.5mm jack plug (U.K. name, known elsewhere by different names...) and then blind type [ E ] and [New Line] to see if it can SAVE to tape (the ZX80 does not use file/program names). There is no need to actually enter a program, the ZX80 will happily save a program with no lines of code! If it’s working you should hear the saving noise...

Mark

Hello Mark. Sadly I don’t have. Is there anything else I can test;

Thank you.

[1024MAK]

Anything else with a microphone input socket?

Or an oscilloscope can be used.

Mark

[Muttley Black]

I find a solution Mark, with pc speakers I had in my basement. Here is a link from the video.

https://vimeo.com/427793850

[Moggy]

For comparison I did a save with my own ZX80 without ram-pack and it made the same nice noise and lasted as briefly as the video so would guess that something is working at least.

The video will be on the quiet side as the zeddy doesn't output the line level signal that the speakers need so the fact we can hear it is a positive sign.

[bola_dor]

I find a solution Mark, with pc speakers I had in my basement. Here is a link from the video.

https://vimeo.com/427793850

Looks good.. I hope I have the same luck.. I 'll check mine tonight..

Have a look at this video about min 9 ..
https://youtu.be/qqUxXrh_xgM
at last hi replaces IC 11 and get ut working. As Issue 2 has soldered ICs is better to refine the diagnosis first. I'll keep whatching this thread and updating on mine as mine hasn't video output either..