Thread: Zx81
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Old 22nd Mar 2020, 11:12 pm   #127
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 8,621
Default Re: Zx81

Agree, you could only practically insert the diode into the video lead if it was one you had made yourself, i.e, by unscrewing the cover of the phono plug at the '81 end of the lead and putting the diode inside there.

Much simpler just to place it between the emitter of the transistor and the video-out terminal inside the modulator. Your 734 reading probably meant .734, the forward voltage drop across the diode, as such that would be an OK reading for a silicon diode. If you measure it on the same range with the probes the other way around you should get a completely different reading, usually '1'. This is also normal.

Assuming this stuff is like the normal diagnostic stuff, does it come with a thin tube (like WD40) so you can aim it more accurately?

If so, get the '81 warmed up, let your fault appear and then with the end of the thin tube about 1cm away from the centre of the chip, fire a series of short bursts until you see a layer of frost form on the top of the chip.
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