ZX81 rebuild, take 2

Discussions about Sinclair ZX80 and ZX81 Hardware
sP1d3r
Posts: 42
Joined: Mon May 16, 2022 9:20 am

Re: ZX81 rebuild, take 2

Post by sP1d3r »

1024MAK wrote: Fri Jun 24, 2022 12:01 am Only if you manage to short the plug tip and ring at the same time :shock:

If only one part of the plug is touching any part of the board or a component on the board, there is no return path, hence no current will flow.
The possibility exists improbably, however!
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1024MAK
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Re: ZX81 rebuild, take 2

Post by 1024MAK »

sP1d3r wrote: Fri Jun 24, 2022 12:37 am
The possibility exists improbably, however!
Of course.

The most fun I’ve had, is with a recreated Jupiter Ace and a ZX81 PSU. I used a RECOM DC/DC converter / switching regulator instead of a 7805 voltage regulator. It has a different type 3.5mm mono socket compared to a Sinclair computer. Because as you insert the plug, there is a momentary spark, the RECOM DC/DC converter gets upset and refuses to output any voltage.

Mind, the spark is impressive, especially if I’m a bit slow in plugging it in.

Hence now I power the ZX81 PSU down before connecting it. No damage has occurred to either the ZX81 PSU or the Jupiter Ace and it still works fine.

Mark
sP1d3r
Posts: 42
Joined: Mon May 16, 2022 9:20 am

Re: ZX81 rebuild, take 2

Post by sP1d3r »

1024MAK wrote: Fri Jun 24, 2022 1:01 am Because as you insert the plug, there is a momentary spark, the RECOM DC/DC converter gets upset and refuses to output any voltage.
I plug the power plug into the motherboard socket before plugging the psu to avoid problems with sparking, none of my psu's spark in this way I've found.

I checked my ULA 2C184E motherboard and there's no output from pin 16 of the ULA.

My other motherboard seemed to have no 5V supply to the modulator but as the PCB track connects more or less directly to the regulator output I must've made a bad connection when I tested it because there was 5V when I tested it again.
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