WG6100

[tb lilley]

Symptoms:
Displays white dot in centre of screen. Neck glow present. HV present. No chatter. Spot killer off. Fuses all test good. PCB (Tempest) tests good (hooked output to a GO5 and picture displays just fine).

Diagnosis:
Shorted power transistor 2N3716 at Q103.

Cure: Replace 2N3716 at Q103 with MJ21193.

 

[Equites]

You broke it again? Sheesh, at least you can fix it.

It did sound like the final output stage was to blame. A bit tricky these frame mount transistors, I'm convinced that with constant expansion/contraction due to heat eventually these can move ever so slight, enough to short against the frame.

A good supply of thermal paste on both sides of the mica can help with heat transfer.

 

[tb lilley]

You broke it again?

Ha! Yeah .... So it seems. Think you're right about those frame mounted transistors moving about. Then again G05 uses the same arrangement and I've never had the same problem on a G05. Who knows .... .?

 

[Muppz]

sleeve the legs with thin silicon tubing, that's what I always do with T03 packages, no possibility of it shorting against the metal then.
Muppz2013-11-16 17:56:40

 

[Equites]

sleeve the legs with thin silicon tubing, that's what I always do with T03 packages, no possibility of it shorting against the metal then.

Hmmm, interesting idea, would heat shrink work you think? How much sleeving to use though?

 

[tb lilley]

It's the screws shorting against the frame that's been my problem in the past. But even that's avoidable if a bit of care is taken and they're then screwed in tight. The holes the legs themselves are threaded through are pretty big .... but yeah, silicon tubing not a bad idea.

 

[Muppz]

hmm not sure about heat shrink, it should work I guess. As for length I mainly used it on 2n3055s mounted on chunky heatsinks so I cut it about 1mm longer than the depth of the heatsink required just to make sure it pushed back against the T03 can when assembled.