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ZX81 video issues

NeXT

NeXT

Veteran Member
Joined
Oct 22, 2008
Messages
8,211
Location
Kamloops, BC, Canada
I inherited this computer from my uncle who died a few years back and it came pretty much boxed with the manuals and cables. I later found a bunch of program tapes for it (well for the Timex 1000 but they are pretty much the same) and all I need now is a matching Sinclair 16K ram pack.
Anyways, I plug the thing in to both a composite video jack and (obviously) get no picture. I also plug it into an RF adapter and try tuning it in but still get nothing. I can't refer to the person who built the computer either because he is dead so I don't know what to do.
Is this common or has something in it failed?
 
The ZX-81's RF modulator is built into the machine. It's video output was designed to plug straight into a TV's antenna input. Try that and see if it shows up on a channel.

Tez
 
wmmullaney said:
And if you would prefer composite, you can check out my Timex thread.

EDIT

linkage
Click to expand...

That is an interesting read and I guess it is worth a try but for now I would just like to get it to work. I have several B/W TVs as well as color TVs. Before I really start to hack away at how video is outputted, I first need it to work.
 
Well I did that, set the tv to channel 34 (according to the manual) and plugged in. I got a little less static bust still no picture. I also checked the other channels and didn't find it.
 
Are you sure that it's working?

maybe you could type in a couple commands then hit the save button, listen on the tape port for any noise. Can you test the PS?
 
It s doing something. if I set it on channel 34 and plug it in, if I jiggle the power connector I can go from a fuzzy screen, to something a little less fuzzy to a solid shade of gray on the screen. the little heatsink in the ZX81 is warming up when plugged in as well and I am using the power supply that was found in the box with the computer which is rated for 9.75VDC, 650ma.
 
The ZX-81 has no bootup message. All you get is a grey screen with an single black blinking cursor on the top left.

Tez
 
Just to clarify, the "boot screen is a

K

at the bottom left.

----
Try this:

1. Set up a system (like an Atari 2600) that you know works with an RF switch and TV, adjust the picture, etc and get it nice and sharp.

2. Replace the Atari with the ZX-81, everything else left the same.

3. If you cannot see a K in the bottom left corner of the screen it *could* be that the Sinclair has a bad video output but, it's more likely that the TV is not equipped to handle the SInclair signal. There is something about how the synch/black signals work. Try another TV, an older one if possible. Only one or two of the TV's I own works with my Sinclair.

4. If you have another TV, start from step #1 again, with a different TV.

Make sure you have the correct channel, 3 or 4.
 
I did this and still didn't get it.
Also, like I said before, I am getting absolutely nothing on channel 2, 3 and 4 (the manual does not even say to tune to any of these channels, ANYWHERE!) and I AM getting a visual response (but still no [K] in the corner] on Channel 34 (which the manual even says you have to tune to).
I have also tried with another B/w tv that requires manual fine tuning (and a screen that makes the one on the Osborne 1 look spacious) as well as two different color tvs that have automatic tuning and a pocket Casio color tv.

EDIT: aaargh!
 
Druid6900 said:
It IS a NTSC model, right?
Click to expand...

I had a feeling something was different.
It could possibly be.
Did the North American manual talk about settings for the UK and europe as well as have excerpts on how The UK uses a UHF system using 635 lines at 50 FPS while the USA uses VHF using 525 lines at 60 FPS?
I have no idea where my uncle bought this thing.

EDIT: Google proves it. There is a PAL version. Is there any definitive way to see what video standard it is currently set for?
 
Last edited:
Probably. I doubt that Sinclair would have printed two separate manuals for such an inexpensive unit.

However, since I've never owned one (and the manual wasn't necessary to repair them), I can't say for SURE
 
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