HV tracking across flexible PCB strips

Jules Richardson jules.richardson99 at gmail.com
Mon May 11 08:40:12 CDT 2015

I really couldn't think how best to word the subject.  I pulled the CRT out 
of the HP 1331 X-Y display that I got the other day, then took all the old 
tape off, cleaned it up, and reassembled with new tape. It's no longer 
arcing around the CRT face, which is good.

However, there's a flexible plastic strip running between the CRT face and 
the chassis which carries three lines (it's a storage tube rather than a 
conventional CRT) and I'm still getting periodic arcing across these lines 
which of course upsets the display's operation. As far as I can tell, 
there's no 'sandwich' (and hence glue) involved - it's just a single 
plastic strip with conductive traces drawn onto it.

Does anyone have experience of these kinds of strips in an HV environment, 
and what (if anything) can be done for them when they start to fail? 
Possibilities seem to be:

1) Try some more cleaning,
2) Reworking with conductive paint (I wondered if one or more of the traces 
have gone high resistance in certain spots and this is encouraging the HV 
to arc between them 'upstream' of such areas),
3) Plastic itself has broken down in some way, requiring replacement; has 
anyone managed to make a replacement strip from scratch?

Although I've not tried the actual X/Y/Z inputs yet, basic 
write/store/erase functionality and beam movement via the front X/Y 
controls seems to be working so long as the arcing isn't occurring, and 
it'd be a fun little gadget to get working.



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