ZX80 US Power Supply Specs?

[martyg]

Just rescued a US ZX80 with no power supply and was wondering if anyone here knew the specs for the power supply? The only info I seem to be able to find is of course for the UK version.

Thanks in advance!


Marty

[Paul]

Hi and welcome in this forum.
I don't know the spec of the US PSU, but I wonder if there might be any reason for differences to the UK version (except for the input voltage beeing 110V instead of 230V).
Any PSU with 9V and at least 500mA, positive at the tip, should do.
I use a small switching PSU stabilized with 9V, 1A for my ZX80 (in Germany). It accepts any AC input from 100V to 250V (really cheap from the supermarket next door).
If you indend to use a Memory extension with dynamic RAM like Sinclairs 16k (for example) the Screen looks better if you use a non stabilized 9V 1A PSU (like Sinclairs) as this delivers approx. 11V if low current is drawn from it and makes the +12V neccessary for dynamic RAM a bit more what it is supposed to be. My PSU gives very thin vertical lines (distortions) every character if I use a 16K Sinclair memory extension.
Without Memory extension 7.5V will do keeping your regulator much cooler.
Please do not use stabilized 12V units as the 7805 Regulator gets really hot then... It is possible to use this as a test for a few minutes without any danger though. The specs of the 7805 allow more than 15V, but it gives a lot of heat then.

HTH
Paul

[Paul]

I just looked it up, typical max input voltage is 35V
but as heat is an issue 11V should stay the maximum unregulated DC input for lang term usage as this was Sinclairs designed for

[1024MAK]

I just looked it up, typical max input voltage is 35V
but as heat is an issue 11V should stay the maximum unregulated DC input for lang term usage as this was Sinclairs designed for

Ah, but what about the poor little electrolytic capacitor on the regulator input (according to the circuit diagram / schematic C8 is rated at 16V)
At 35V it would most likely go BANG or POP and make a nice mess all over the inside of the Zeddy

The rest of the advice that Paul gives is however sound advice

The minimum input voltage needed for a ZX80 or ZX81 without an external RAM pack is 7.5V dc from a regulated power supply.
You could use a cheaper unregulated unit, but you would have to check the output using a meter, as the output voltage from these when not connected to a load (e.g. your Zeddy) is higher than when a load is connected. I suggest that you would want to set it to give about 8V with the ZX81 connected (the voltage should be a bit higher than 7.5V to allow for the ac ripple as these are non-regulated).
In both cases the heatsink on the 7805 5V voltage regulator will still get warm, but not as hot as when using a Sinclair "9V" PSU (which are unregulated "9V" units).

If you intend using a external RAM pack, as Paul says, you are best with a "9V" unregulated PSU which produce about 11V dc when connected to a ZX80 or ZX81. Having looked at some of the circuitry for the Memotech 16k RAM pack, I noticed that it uses extra capacitors to smooth the "9V" unregulated line to produce a so called 12V line. Some other manufacturers use similar arrangements. No magic here, as the voltage on the "9V" line is about 11V dc and this is within the 10% of 12V that the DRAM chips need.

Oh, and always double check the polarity

Note that the voltages quoted here for unregulated power supplies are the readings you get with a multimeter (voltmeter) and not what it says on the rating plate of the power supply. Where I refer to the voltage on such units I have put it in quotes like "9V".

Mark

[Paul]

I just looked it up, typical max input voltage is 35V
but as heat is an issue 11V should stay the maximum unregulated DC input for lang term usage as this was Sinclairs designed for

This is, as Mark already stated, only the max rating for the 7805, not the Rest of the ZX80
The voltage allowed for the capacitors may vary from device to device

[AndreSan]

Hi - I am in possession of a zx80 in seemingly very nice condition. I'd like to sell it, but before doing so, I want to test. I have read many of the posts in this thread and come away with a rather pedestrian question: What is the spec on the jack? is it 5.5mm x 2.5mm? I am not hugely familiar with this stuff, so thank you for pointing out what must be obvious to everyone else.

I have found a power supply that I like except that it is regulated. I seem to remember some advice that an unregulated supply is preferred. Please advise.

I like the supply as it is voltage adjustable 4.5 - 12 V. Clearly I'd have to be careful not to peg the supply on 12V, but it solves the problem of providing an optimal voltage based on if and what peripherals are being driven by the zx80.

The supply is rated 10Amps, but I don't think that should be a problem. Pleas advise.

It also has a polarity converter. Please remind, the Sinclair is GND on the outer barrel and (+) at the pin?

Thank you! My goal is to get this in the hands of a member of your community following an accurate description and a fair price, and to have a bit of fun in the process.

[1024MAK]

Hello and welcome

What is the spec on the jack? is it 5.5mm x 2.5mm?

No, it’s actually a normal mono (TR or two contact) audio jack plug (also known as a mini phono plug), the outside diameter of the connector has a diameter of 3.5 mm (0.14 in). This Wikipedia article shows a photo of them (amongst the other sizes and types in the same family).

The tip (end) is positive +
The sleeve is negative - or 0V/GND/ground

I have found a power supply that I like except that it is regulated. I seem to remember some advice that an unregulated supply is preferred. Please advise.

The ZX80 does not care if a the DC power supply unit is an unregulated or a regulated type. Either will work. It’s more complicated if you are using a RAM pack.

I like the supply as it is voltage adjustable 4.5 - 12 V. Clearly I'd have to be careful not to peg the supply on 12V, but it solves the problem of providing an optimal voltage based on if and what peripherals are being driven by the zx80.

Set the output to between 7.5V and 9V (inclusive).

The supply is rated 10Amps, but I don't think that should be a problem.

10 Amps is a bit excessive, the ZX80 only requires less than 1 Amp.

It also has a polarity converter. Please remind, the Sinclair is GND on the outer barrel and (+) at the pin?

The tip (end) is positive +
The sleeve is negative - or 0V/GND/ground

Mark

[AndreSan]

Mark - thanks so much. Got it on the mini phone and polarity.
I do have a 16K ram pack and now that you mention it I remember that was part of the post that discussed unregulated. I will keep looking for PS that works.
I do house wiring, so that is some dim-witted stuff compared to this, but a 13W LED as the only load on a 20A circuit isn't a problem, so that's why I wasn't concerned about the amp rating of the PS.

Now on to other items for other threads.

Thanks again,

Andre

[1024MAK]

If it’s a Sinclair or Timex Sinclair 16K RAM pack, that should work with a unregulated PSU that has an output voltage of between 7.5V and 9V. For a regulated PSU, the output should be between 8V and 11V.

For other makes/names/brands of 16K RAM pack, it’s better to use either an unregulated PSU that has an output voltage of 9V or a regulated PSU with an output voltage of 11V or 12V.

Here’s a photo of the 3.5mm jack plug with the polarity:

ZX80 / ZX81 power plug polarity

Mark

[1024MAK]

So, just for kicks, here’s my ZX80 telling you how much power it needs…

ZX80 saying how much power it needs…

At a supply voltage of 11V (from a regulated PSU as it happens), it draws about 0.38A.

Note the wonderful picture quality is down to the video being via UHF RF as I did not have my ZX8-CCB to hand (this board has not had the video modified by me).

Mark