Selling a ZX81 - should I see if it works?

[detrain]

I have offered to sell a ZX81 for a friend who has just found it in her late father's house. It has been kept indoors in its original box, but probably not plugged in for nearly 30 years. Physically it is in good condition.

I am inclined to sell it as untested, with the plug removed and a suggestion that the buyer check it or have it checked by an electrician before applying mains power. If I did try it, this would be limited to seeing if it produces a picture I can tune in on the TV - I have no program cassettes or tape recorder leads for it.

My concern is that if I plug it in I might fry it because of dried-up capacitors or other faults that a purchaser could check out first. I know this is an issue with valve radios, record players etc. and collectors prefer to buy these untested, but do similar concerns apply to items like this? If you were wanting to buy a ZX81 what would you have me do?

[Nickthedentist]

Hi John,

I don't think plugging it in would cause any damage, and suspect that most potential purchasers would prefer to know that it show some signs of life (albeit not fully tested).

If you can get a picture on your telly, and the keyboard seems to work, chances are it will be OK.

Nick.

[Outrun_uk]

I'd be tempted just to plug it in and see what happens. The mains PSU is a simple design, transformer, bridge rectifier and a smoothing cap. The regulation is done inside the machine with a linear regulator chip. You may find it works fine, the Sinclair machines are pretty robust age-wise. One issue may be no response from the keyboard as the material used to manufacture the membranes seems to deteriorate with age but replacements are (or were last time I looked) available.

HTH

Kev

[SiriusHardware]

If I see an item advertised as 'working the last time it was used but I have nothing to test it with now', that to me is barely disguised code for 'I am not prepared to say that this works'. A lot of things definitely don't work are advertised with this or similar wording.

If a seller is prepared to state unequivocally that something is working, then I am usually prepared to offer more for it. I'm sure most people think that way, so if you want to get more for it, try it, and say that it is working if it does seem to be.

[ralph2472]

Yes, definitely check it out, and take a photograph of the TV screen to show that it was working when you tested it. That way, I'm sure that you'll get more money for it. If it doesn't work; you've lost nothing because you can advertise it for parts. In fact, I've been surprised on several occasions when I've sold something as faulty and got more for it than a working example.
The World is a weird place.

Regards

Ralph.

[crusher19860138]

Modern capacitors are nothing like the old wax paper types found in old valve radios, plug it in,you will find all's well!

Please let us know if it does work.

[detrain]

Thanks for the advice - as there are 6 responses in favour of trying it out and none against, I plan to try it and photograph it (including the TV picture if it does work) at the weekend. I will respond again with the outcome.

[Billy T]

I wouldn't let an electrician anywhere near vintage solid state electronics unless I knew he understood fully the technology and the risks.

Incorrectly applied, the standard insulation tests could fry it.

Cheers

Billy

[SiriusHardware]

Originally Posted by Billy T

I wouldn't let an electrician anywhere near vintage solid state electronics unless I knew he understood fully the technology and the risks.

Incorrectly applied, the standard insulation tests could fry it.

Cheers

Billy

In actual fact, PAT testing strictly only needs to be applied to the box / thing that the mains goes into. In the case of a desktop PC with integral PSU, that's basically the whole PC.

But in the case of a Laptop or in this case a vintage ZX81, both with external PSUs, only the PSU should be PAT tested without the laptop or ZX81 anywhere near it.

The ZX81's PSU is just an old fashioned iron cored transformer with a bridge and a big smoothing capacitor on the output side, so its prospects for surviving electrical testing are quite good. It's also double insulated and fed with twin core flex, so there is no earth to consider. The earth pin on the mains plug is not used.

[Gulliver]

Another voice in favour of checking whether it works. You cannot really damage it by doing so. Be aware that the ZX81 (especially early versions of it's ULA) outputs a signal that is not always readily decyphered by modern televisions. As the computer has no sound output, or other outward signs of life except the image on the screen you might like to use an older CRT TV if you have one.

Aslo be aware that the PSU might have died, consider trying a modern generic unit.

They're not worth a whole lot but you will get more interest if you can sell it as working, rather than "worked when put in the loft in 1983". There is quite a large user group for these machines. I have two working examples, including one of the very earliest (dated March 1981).

[Gulliver]

As a point of interest was there any hardware of software with it? I would potentially be interested depending on the items.

[detrain]

I am planning to test and photograph it with my Toshiba 140E4B portable TV (a 21st birthday present in 1986), which is almost as retro in its own right, but not for sale!

There is a manual and a book with it, but no program cassettes or other hardware.