HV tracking across flexible PCB strips

tony duell ard at p850ug1.demon.co.uk
Mon May 11 12:23:31 CDT 2015

> I agree, it does seem strange! On the chassis side, there's a rather unique
> terminal clamp which holds the end of the flexible strip. One of the wires
> (I expect it's for the CRT anode) on the other side of that clamp is
> obviously HV cable, but the other two appear to be nothing special.

That does sound strange. Given that the final anode voltage is going to be
10-20kV, I would not expect it to share a connector with anything.

[As a counterexample in the HP monitor for the HP9836C there are 2 HV-ish
connections between the flyback stage and the CRT base -- one is about 1KV
the other 5kV. These have their own in-line connectors, other signals
go over the backplane. But here the 2 HV wires do not share a connector with
each other, let alone with anything else).

> Yes, that had crossed my mind - my only worry is soldering at the CRT end
> as I'm not sure if there's a danger of damaging something within the CRT.

The biggest worry is cracking the CRT glass either because the pin and glass do
not expand at the same rate over all temperatures (the metal and glass are chosen
so this is the case over normal temperature ranges for obvious reasons, but not
for soldering temperatures) or because you heat one bit of the glass and not others.
In general soldering to a pin close to a glass-metal seal is a no-no. Is there room to
put a pair of pliers on the pin (between the CRT and the joint) to act as  heat shunt?

Don't worry about the stuff inside the CRT. You will not find soft solder in an evacuated
object, it would 'boil off'. Internal connections are spot-welded. The whole lot will have
been heated to red heat or so (induction heated) to out-gas it when the thing was being
pumped down anyway.




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