‘Tatung 81’ (ZX81 in a case)

Discussions about Sinclair ZX80 and ZX81 Hardware
Lardo Boffin
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Joined: Sat Nov 26, 2016 2:42 am

‘Tatung 81’ (ZX81 in a case)

Post by Lardo Boffin »

Hello all

I just bought this ZX81 in a cool case, which sadly was not well packed and got a bit broken. :cry:

The shape reminds me of Tatung Einstein hence the title:
E7E55577-1F50-4065-B5E1-84475E2FC07A.jpeg
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Lardo Boffin
Posts: 2160
Joined: Sat Nov 26, 2016 2:42 am

Re: ‘Tatung 81’ (ZX81 in a case)

Post by Lardo Boffin »

Breakage here
437F6D9C-FE35-4636-A9BD-F22950147E24.jpeg
and here…
F8F6BDF7-C678-4CAB-B8C3-467CE26D867E.jpeg
And a few others.
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Lardo Boffin
Posts: 2160
Joined: Sat Nov 26, 2016 2:42 am

Re: ‘Tatung 81’ (ZX81 in a case)

Post by Lardo Boffin »

Hope fully it will glue ok. The inside got a bashing as well.

There are two power sockets:
E22CFC8A-8E7E-4D76-B4F4-9B4898BC9AA6.jpeg

As far as I can tell they appear to be joined together so I only need to use one?

FE321723-AA59-4BA2-9BA6-EE7B3B14EEE1.jpeg
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Lardo Boffin
Posts: 2160
Joined: Sat Nov 26, 2016 2:42 am

Re: ‘Tatung 81’ (ZX81 in a case)

Post by Lardo Boffin »

My main concern is making sure it is safe to switch on as the power conversion is done inside the case!!

73E039DF-D24D-4768-9E62-EC20CC213438.jpeg

Is there anything I can check before I take it to the garage and put it on the concrete floor and switch it on from a distance?

None of the power stuff appears to have come lose.
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Lardo Boffin
Posts: 2160
Joined: Sat Nov 26, 2016 2:42 am

Re: ‘Tatung 81’ (ZX81 in a case)

Post by Lardo Boffin »

There is also an interesting board I have temporarily removed:


A 16K RAM pack plus?

C87F9B9D-B920-4F29-9340-5F0D51367D69.jpeg

Close up of the chips.

9E47819A-CE72-473D-B771-9B4360B51597.jpeg
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
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BarryN
Posts: 151
Joined: Thu Nov 09, 2017 11:34 pm

Re: ‘Tatung 81’ (ZX81 in a case)

Post by BarryN »

If you are comfortable and proficient using a volt meter unplug the connector going to the 9V in jack on the ZX81 board (the black plug), switch the power on and check the output to that plug with a volt meter. It should read between 9V and 12V DC. Check it on AC V and it should read 0.

If you are not comfortable or proficient using a volt meter, or are not properly trained to handle electrical equipment, please have someone who is properly trained perform this test for you, since there are exposed wires there carrying 240VAC and that can KILL you.
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1024MAK
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Location: Looking forward to summer in Somerset, UK...

Re: ‘Tatung 81’ (ZX81 in a case)

Post by 1024MAK »

The first thing to say is that all of the following is based purely on what I can see from your ‘photos...

It’s difficult to tell from the ‘photos, hence me writing this here. There should be at least 5mm separation between any of the mains wiring (but not including the earth wiring) from any low voltage wiring or low voltage terminals or connectors. Obviously don’t measure this or touch any of the mains wiring while it is connected to the mains supply!

If any of the mains wiring is not 5mm clear of any of the low voltage wiring or connectors/terminals, use cable ties or some other plastic fixings to move it and keep it clear.

Both the mains wiring and any nearby low voltage wiring should be restrained so that neither can come within 5mm of each other.

The round black ‘mains’ connector looks like a Belling Lee power outlet (it may have the stylised BL letters on it). The way it is fused is partly why I have come to this conclusion. If it is a Belling Lee power outlet, these have been out of production for at least five years. So they, along with the matching plug are rare and expensive :(

This outlet may have been used for the mains supply for a monitor.

Looking at the ‘photos, the power supply uses a conventional 240V to low voltage transformer. This then feeds a PCB with large smoothing capacitors. Before feeding the ZX81 board. The PCB with the large with large smoothing capacitors must have some rectification diodes or bridge rectifier somewhere... And it looks like there is either a regulator or a transistor in a TO220 package for the output. It would help if you could take some better ‘photos of it.

Apart from uninsulated terminals (which was normal back then), I can’t see anything obviously wrong here. It’s very unlikely anything will go bang and explode in your face.

So power it up and see what happens. Just keep your fingers away from any of the mains connectors, terminals, fuses and wiring.

In regards to the expansions, one is an uncased Sinclair 16K RAM Pack. The hand wired board is an input/output board. The two large chips are PIO (parallel input/output) chips made by Mostek, type number MK3881N. I think these were made under license by Mostek and are equivalent to the Zilog PIO chips. There are datasheets for the Zilog PIO chips here ;-)

Mark
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Lardo Boffin
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Joined: Sat Nov 26, 2016 2:42 am

Re: ‘Tatung 81’ (ZX81 in a case)

Post by Lardo Boffin »

Thanks both.

Closer on the power PCB:

7BF73451-59E2-4EC6-AAC2-AD9838B8A13D.jpeg


I can’t get a photo of underneath without removing it but it looks like maybe a voltage regulator type thing under there (edit - which I see you mentioned in your post).

EB6B45E9-02B3-4673-8574-F8CF746AC8CE.jpeg
Last edited by Lardo Boffin on Fri May 28, 2021 9:12 am, edited 2 times in total.
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Lardo Boffin
Posts: 2160
Joined: Sat Nov 26, 2016 2:42 am

Re: ‘Tatung 81’ (ZX81 in a case)

Post by Lardo Boffin »

Front and back of the socket:
BB41C430-E8D4-4B13-9E7D-7DF24DD5AEE8.jpeg

Good old RS components!
7234815C-3FA4-4D1F-B0F0-8A3684D45C58.jpeg
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Lardo Boffin
Posts: 2160
Joined: Sat Nov 26, 2016 2:42 am

Re: ‘Tatung 81’ (ZX81 in a case)

Post by Lardo Boffin »

Plugged in and switched on - no explosions! Also very little voltage at the 9V plug by the zeddy. About 0.08 so not much going to happen there!

Hey ho.
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
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