Sinclair ZX80 / ZX81 / Z88 Forums

Hi at all,

I ask to the ZX81 user is never happens for distraction, to insert the power jack, on the ear or the mic connector.
And sadly power up. On ear and mic connector is any type of DC block protection?

Thanks,

Matteo

Yes, surely the worst design mistake from Sinclair on the Zx81... (Spectrum?) !
Use same socket with ear/mic, and the 9v power supply…


I've been wrong many times before.

Thanks Xavsnap.

And this have damage your ZX81?
You have immidiately power off the brick?

Thanks.

I had to unplug it… no pictures !
No, the mistake seem to be … safe for the ULA ship.
C10 & C12 can isolate the ULA, but in the french display mod, the transistor TR3 can be toasted by the 9v voltage on the Mic socket.

You have shot the ULA and the Z80?

Sorry again.

No, the jack return to the right place…
And the computer start properly.

But, in the real world, the Mic and the Ear jack was connect at any time, and the power socket was the only one to be feed !

No, the main problem is to invert the power supply polarity… it's a component firework… RAM, ULA, the regulator…

Thanks so much Xavier.

Yes if you have reverse polarity is a tragedy

Thanks,

Matteo

Inserting the 9V DC power plug into either the Ear or Mic sockets does no harm to the ZX81. The ULA is the other side of DC blocking capacitors, so is unaffected.

Looking at the schematic for the French version, I can’t see how transistor TR3 would be damaged.

Mark

At a second look, the R31 resistor isn't shunted.
It's safe on the Mic socket too on the french board.

XavSnap wrote: ↑Mon Oct 19, 2020 8:11 pm At a second look, the R31 resistor isn't shunted.
It's safe on the Mic socket too on the french board.

Xav a another info,
the Belgian ZX81 are the same for the French market?

Thanks,

Matteo