Thread: Zx81
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Old 29th Apr 2020, 7:14 pm   #293
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 9,291
Default Re: Zx81

Assuming the IC socket is out and all the holes are clear:-

Carefully scrape the 'resist' (the red stuff) off around 5mm - 10mm of the track leading away from the pin 20 pad on the top side of the PCB. Ideally, pick a track which will normally be under the IC so that the repair will not be visible when the IC and socket are in place.

Take a 1" to 2" long strand of very fine uninsulated wire, feed most of it through the pin 20 hole from top side through to bottom side and fold the very end of it over, flat, so it lies along the bared bit of track, and solder it to it. Keep the soldering as low profile / flat as possible so it does not prevent the socket from being refitted afterwards. Be careful not to let the pad / hole fill up with solder otherwise you'll have to remove the wire, clear the hole and start again.

If you've done it right, you now have a fine strand of wire soldered flat along the track on the top side, turning sharply at 90 degrees and dropping through the pin 20 hole and emerging out of the hole on the underside of the PCB.

Now refit and resolder the socket, leaving pin 20 until last. When you get to pin 20, you should have the IC socket pin and the thin wire strand both coming through the hole side by side.

What you do next is determined by how pretty you want to make the job look, but the simplest compromise is to wind the thin wire several times snugly around the IC socket pin and then solder it, cutting off any excess length afterwards. By doing this, you reinstate the missing connection between the IC socket pin and the track on the top side.

A good source of very fine strands of wire is a piece of thin insulated multistrand wire - strip about two inches off the end and fan out the individual stands of wire, select one strand only and cut it off. Essentially, the wire you choose has to be fine enough for both it and the IC socket pin to fit through the hole side by side.

Last edited by SiriusHardware; 29th Apr 2020 at 7:40 pm.
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