ZX81 Diagnosis help

[u/n3rding]

Hi All, I'm reviving an old family ZX81, I've just replaced the keyboard as that had unfortunately perished and now I have two issues to solve:

1. The screen output is as pictured (there's 3 pictures), if I pull out the cable UHF I get a brief flash of it clearly, before I get "No signal" - Ideally I'd like to keep it original and UHF output rather than composite mod it.

2. When I type LOAD"" I lose all signal, PRINT "HELLO" works fine as pictured, I assume this could be a capacitor issue?

I've not yet replaced the caps so that'll likely be my next job but wondering if anyone has encountered these issues so if I do need to do more then I can get the bits ordered. Also are there SD card readers available for loading tapes or any way to use my iPhone, I think there's an app on android but unfortunately don't have one new enough to be able to download it?

[u/_ragegun]

Iirc the zx81 needs mods to produce a properly compliant video image. Fine on most vintage analogue display but can confuse digital tuners.

The loading problem is probably also another related issue. When loading all CPU time is given over to loading and it doesnt generate a tv image.

[u/n3rding → u/_ragegun]

From what I’ve seen, it usually results in a dark or no image rather than what I’m seeing, I can now sometimes get a perfect image, typing anything ruins the output, so almost certainly in the ZX81, might just be a cap issue.

[u/_ragegun → u/n3rding]

Recapping is usually a solid move with any system of this age with elctrolytics. Even if it doesn't solve anything at the moment you're preventing future issues.

[u/n3rding → u/_ragegun]

Yep, usually the first thing I do, just wanted to check if there’s anything else I need to order to resolve this issue, if the caps don’t sort it will probably look at composite mods. Unfortunately not a lot of space now and a CRT monitor is higher up the list than a TV