Hi all,
I bought a Sinclair ZX81 on a garage sale some days ago for around 12 USD as a non-tested item as the guy said he had no wires to even try and run it. I have a couple of RF cable kicking about from my Atari 2600 and ZX Spectrum, so I have this basis covered.
According to the manual LINK it takes 9V 700mA unregulated (I'm not sure what it means) 3.7mm jack power supply. I have a 9V DC 1A jack power supply I bought for the Atari (it's not an original one - a unbranded one) and I tried to use it, but to no success. Manual tuning my TV same as with Spectrum and Atari, and no signal.
I was wondering if maybe the power supply is not up to spec? I was thinking that maybe 1mA is too much to power it up? But I went online to look for an unbranded ZX81 power supply and they are running 2A so I'm not sure what's going on here.
Is it busted? Or should I get one of those unbranded power supplies that say they are made for ZX81 to test it?
Thanks :)
1A might be too much. You’ll also need to ensure the polarity is correct. There should be a label, usually co-located with the serial number, which states the input and polarity requirements of the DC plug.
No, higher current rating is not a problem. However, higher voltage is.
So if I already connected it, does it mean it ruined the computer?
They are selling replacements that are rated 2A:
The higher amperage rating is not really relevant - that just indicates the max current that the power supply can provide. If the device pulls less than that, it isn't a problem.
However, the polarity of the power supply is very relevant. If it's is the opposite of what the ZX81 needs, and you powered it up, then yes, you may have damaged something.
The polarity should be shown on the power supply - usually it's a diagram with three circles which illustrate which part of the connector is positive and which part is negative. There is often times one on the piece of equipment as well. Those diagrams need to match.
It really depends on the internal tolerances. If you are familiar with basic circuitry and the use of a multimeter, you can check for initial power continuity.
Otherwise, using the correct amperage and polarity power supply will be the easiest check.