Tektronix TAS 485 - bad menu button, flex PCB (solved)

[beowulfenator]

Hi!

I just got a used Tektronix unit and it turns out one of the menu buttons is not working. Apparently the traces on the flex PCB have been rubbed off!

Is there a good way to repair this flex PCB?

Thanks!

[wraper]

Try to replace destroyed carbon traces with conductive glue.

[philpem]

Mask with Kapton tape to form the track pattern, then paint over with silver paint (the stuff used for repairing flex-PCBs and TV remotes).

When it's dry, remove the tape, apply fresh tape for the pattern on the other side and repeat the painting.

Keep the layer thin so it doesn't impede the button, but not so thin that there's almost nothing there. A glue spreader used as a squeegee might help (with that technique, the kapton tape will set the layer thickness).

[beowulfenator]

Any recommendations to the specific brand of silver paint/glue?

[beowulfenator]

I've successfully repaired it using some conductive lacquer:

http://termopasty.pl/en/products/graphite-varnish-en/

Surprisingly, the resistance of this lacquer is actually quite high - on the order of kiloohms in traces several centimiters long. But then it is comparable to the resistance of existing traces on the PCB.

Adhesive tape as a template worked reasonably well. The first time I applied this lacquer the layer was too thin apparently, but then i added more on top of what I had and it all worked fine. I wasn't able to reproduce the thin traces (two interlocked "fingers" coming from each side), so i just laid two thick tracks next to one another.

Thank you all for advice!