CTC-16 Green Picture

[Jon1967us]

Originally Posted by Electronic M

Sometimes the focus rect tube will test good but not work well. I tend to parallel a modern 5KV diode across the focus rect tube as an early troubleshooting check/long term fix.

A few things to watch out for in focus circuits. Corrosion inside the CRT socket and or bad contact between socket and CRT, the 66M resistor, the 6KV ceramic cap on the focus coil can have issues...The collector that reported it had an tuning eye type cap checker and said it didn't fully open the eye on the capacitance test.

When I heard the quick arcing/snapping/zapping sound, when the focus went out a couple days ago, it seemed to be coming from the chassis or HV area, not the CRT socket, but I'm not 100% sure. Still need to check voltage at CRT and definitely that cap and the bleeder.

[zeno]

Old trick for arcing was turn off the AC & open the shop doors on a
humid day. Sometimes just blowing on it will trigger it.
Trouble is everything in the focus is known to go bad.
Arcing was usually the socket or filament winding. Keeping one of the
stick rectifiers around is handy for test or eliminating the tube & socket.

73 Zeno
LFOD !

[Jon1967us]

Originally Posted by zeno

Old trick for arcing was turn off the AC & open the shop doors on a
humid day. Sometimes just blowing on it will trigger it.
Trouble is everything in the focus is known to go bad.
Arcing was usually the socket or filament winding. Keeping one of the
stick rectifiers around is handy for test or eliminating the tube & socket.

73 Zeno
LFOD !

It's humid here by the coast. Could've been some condensation, or maybe an increased load due to having the supply voltage to the color amps out of circuit that could've compromised the focus components - hard to say. Checked (dialed down) the screen drives against service mode, but that didn't affect focus.

I did measure 4KV at the focus CRT pin - so that may be a little low...

https://ibb.co/jy0BFp8

Not psyched to pull the chassis for the 168th time, but I need to check the windings and other stuff for drift and leakage

Pic
https://ibb.co/0qBwfJr