3 connections below power jack?

[mrtinb]

Hi

The three connections below the power jack. One is ground, one is 5V. What is the middle one for? And where is it connected?

[mrtinb]

[dessony]

These 3 holes were used for the switch going to an RF video modulator used in the T/S1000. The video modulator had two different channels. Channel 3 and Channel 4.

DesSony

[mrtinb]

So the middle hole is not connected to anything on the UK ZX81?

[1024MAK]

So the middle hole is not connected to anything on the UK ZX81?

If a U.K. standard E36 modulator is fitted, or no modulator is fitted, yes, one of those three holes is not connected to any other circuitry.

You can see the channel select switch in the top left of the schematic in this thread

Mark

[dessony]

Correct. The American RF video modulator has two choices. A middle hole is an input to the switch between Ground and 5+. We used Channel 3 or Channel 4 on the American old CRT TVs. Please check the schematic area around the RF video modulator. Mark(1024MAK) is right!

DesSony

[dessony]

That is what the American owners see when they have to open their systems for any repair works! On my system, I just removed the modulator's "3 holes" insulation on the left side of the picture.

DesSony

[mrtinb]

I’ve just soldered a pin header to the 3 holes, and connected the hole at the end of the pcb trace from the middle hole, to the composite signal.

So now I have a pin header with GND/Composite/5V

[mrtinb]

Then I have a fine Dupont header connection to PokeMon’s ZX8-CCB.