Sinclair ZX80 / ZX81 / Z88 Forums

Hi all,

I have a ZX80 which doesn't seem to be powering on. Having never owned one of these before I really don't know if there is any indication of when the ZX80 is actually on, so I just assumed it was and tried to tune it into one of my several CRTs but to no avail.

Now I'm thinking it's the Power Supply which is the original ZX80 one which is the problem. So before I go on the hunt for one does anyone have any troubleshooting techniques or processes I can go through first?

I have opened her up and all seems clean and tidy.

Thanks

Have you got an old black & white CRT? You might struggle to get any image on a colour TV

I guess one of the tricks I have never seen on here (does it work?) would be to connect some earphones to the MIC socket and enter the SAVE command to see if you hear anything...

RWAP wrote:Have you got an old black & white CRT? You might struggle to get any image on a colour TV

I guess one of the tricks I have never seen on here (does it work?) would be to connect some earphones to the MIC socket and enter the SAVE command to see if you hear anything...

@Rich

Not enough grunt from the 80 to power earphones I would have thought Rich.


Hi Shane welcome to forum.

As for trouble shooting advice, In a short while I suspect Mark (1024MAK) will bump into this thread and will be able to answer all your questions, as like many other forum members he is not only knowledgeable but has a great knack for explaining things in a way that even a dummy like me can grasp.
(Not implying you're a dummy by the way just a term I reserve for myself )


Regards.

Moggy

If you have access to a multimeter, you can use the DC Voltage range to test the output from the PSU. With it not connected to the computer, the output should be a lot higher than the rated 9V.

If you don't have a meter or know someone that has a meter that can help, there are a couple of other tests. Very carefully open the case enough so that you can touch the metal heatsink inside with your finger (or use a thermometer). Connect the power supply to the computer and switch on. Leave it on for about 30 minutes, or until you notice the heatsink getting hot. The heatsink helps the 7805 voltage regulator chip dissipate unwanted energy in the form of heat, so it can produce a nice smooth regulated supply voltage for the rest of the computer circuitry.

If you don't want to open the case, you can still do the above test, you will just have to wait longer so that the heat has a chance to warm up the outside of the case.

If the heatsink / case gets warm, the PSU and regulator are either working, or partly working.

If you have an audio system with a sensitive microphone input, and you have a suitable lead for it with a 3.5mm mono jack plug on the other end (stereo is no good), you can connect this to the mic socket on the computer. Reset the computer so you know that if it is working it is waiting for your input. Then press the key to enter the SAVE command (see the manual for details). The ZX80 should then try to save a small file. As the memory is mostly empty, the sound caused by this will not last very long... so don't miss it! If you heard a squeal type noise, the computer is mostly working.

As said above, the best display for a ZX80 is a monochrome (black and white) CRT (glass tube) TV. Only when waiting for input will the ZX80 actually display a TV picture. When processing BASIC programs, no picture is produced, so the screen display disappears.

Some colour CRT TVs will work, but it's a case of luck finding one that will. Same applies to more modern TVs. Most just don't like the non-standard TV signal generated by the ZX80. There are some solutions to some of these problems, but that's for a later discussion.

Mark

Hi all,

Thanks for the replies, I've been mega busy the past couple of days getting machines ready for display in my new premises so havent had the chance to try the processes suggested by Mark. I'm very thankful though and will hopefully get around to it again mid week.

I'm quite happy opening up the ZX80 I did so earlier in the week to see if the usual giving a good clean would sort it but I understand now it's probably the selection of TVs I've tried it out on bring the cause.

I think I've got a suitable cable, I use it in my connect my Sega mega cd/Megadrive/32x setup so that's definitely a viable option.

I will update you once I've tried everything.

Ttfn

Shane