Zx80 RF issues

[jb1972]

Hi, I’m new to the forum. Have owned Sinclair computers since I was a kid in the 80s but recently got interested again and have been steadily growing a small Sinclair collection. I just added a couple of zx80s one of which puts out a very dark display. Might be something terminal with the RF unit or might just need a clean. I noticed some build up in the RF terminal which makes it difficult to get the lead all the way in. As a first fix attempt, can anyone recommend how I could go about safely cleaning the RF terminal? Is some ethanol ok to use? Thanks in advance for any guidance.

[1024MAK]

Isopropyl alcohol (IPA) or a solvent cleaner based on this is often used for cleaning Printed Circuit Boards and electronic components. So if it's just dirt and gunk, using IPA should help.

You need the type intended for industrial use (purity of over 99%).

A ZX80 (and a lot of the ZX81s) will show a dark screen with poor contrast on a lot of colour TVs. This is because ZX80 and some ZX81 computers don't include the "back porch part of the video signal. Which us what most colour TVs need to automatically work out the black signal level.

This may the real cause of your problem.

Mark

[jb1972]

Thanks Mark - so if I am really going to get into the zx80s I need a black and white telly? I’ll try a bit of a clean first though before I go trawling on eBay!

[1024MAK]

A few points:

Yes, a black and white TV should work, but good luck finding one.

If one ZX80 works, but another does not, then can you see and difference between the different boards? One may have a modification or one may have a fault.

Some colour TVs do work correctly with a ZX80 (I know, I have one). So if you have more than one TV, try some others.
Or if you intend using composite video, a extra module can be used which adds the missing "back porch" to the video signal, hence allowing a colour TV to work with it (well, most colour TVs). I recommend the ZX8-CCB.

Mark

[jb1972]

managed to sort out the RF issues by cleaning the port and managing to find a lovely old black and white portable TV off ebay for £20. Now getting a lovely crisp picture and loving the screen flicker after every key stroke! have a couple of programming books to work through - i shall be creating static blocks in no time - lol

[1024MAK]

Have fun now

Mark