GE 805 Focus Coil Question

[Chris K]

C270 is a 0.2uf original wax cap. I'll replace it.

Reads 0.3uf and it leaks at 25 volts. It's a 400V capacitor

[jr_tech]

Originally Posted by Chris K

The cathode voltage does vary from 130 to around 260 when the brightness pot is turned to the halfway position. G1 doesnt change nor does G1

I suspect leaky/shorted caps in the circuit surrounding the brightness control.

C-303 would be my most likely suspect.

jr

[Chris K]

Originally Posted by jr_tech

I suspect leaky/shorted caps in the circuit surrounding the brightness control.

jr

The first one certainly was. I bumped it up to 450 volts for a few seconds on the capacitor tester just to be sure it was full of electrons but no eye opening at 25V.

[Chris K]

That did it...changing those caps! A slight adjustment of the ion trap and I got a bright static picture in good focus. Fantastic. Thank you for all of your help!

[Chris K]

Looks like the brightness pot is shot. It only works turned all the way up. Once it's moved from the extreme brightness position, it goes dark. It's a 500k pot but it's double shafted and ganged with the contrast pot. I think Ill put a new carbon linear 500K pot on the back of the chassis for brightness and leave the original pot in place as an inactive control for the aesthetics. Once I set the brightness, there's little need to screw with it anyway and I'll position it so it's accessible from the back of the cabinet.

[jr_tech]

Have you checked the pot with an ohm meter?

jr

[Electronic M]

Mark Oppat should be able to make you a new control given enough information.

[Chris K]

Originally Posted by jr_tech

Have you checked the pot with an ohm meter?

jr

No, not yet. I have another one of these and the brightness pot failed on that one as well. I wonder if this is a design issue. I will check it but what else could account for the lack of adjustability?

[Chris K]

Originally Posted by Electronic M

Mark Oppat should be able to make you a new control given enough information.

The name is familiar but I don't know who that is nor do I know how to get in touch.

[Chris K]

Found it and the website. Thanks Tom

[Chris K]

There's another issue with the TV but IDK if I should make it a separate topic. The vertical deflection is lopsided. The bottom of the picture is level left to right but the height of the picture is lower on the left side than on the right, about an inch lower. I tried yoke and focus coil manipulations to no avail. It's the same on the 10BP4 and the 5" technician tube so it's not focus coil position since the 5" doesn't use it. Any thoughts anyone?

[jr_tech]

Originally Posted by Chris K

There's another issue with the TV but IDK if I should make it a separate topic. The vertical deflection is lopsided. The bottom of the picture is level left to right but the height of the picture is lower on the left side than on the right, about an inch lower. I tried yoke and focus coil manipulations to no avail. It's the same on the 10BP4 and the 5" technician tube so it's not focus coil position since the 5" doesn't use it. Any thoughts anyone?

I suspect crosstalk between horizontal and vertical circuits...possibly a filter cap on a power supply shared by both is not doing its job. Do you have an oscilloscope?

jr

[jr_tech]

Originally Posted by Chris K

No, not yet. I have another one of these and the brightness pot failed on that one as well. I wonder if this is a design issue. I will check it but what else could account for the lack of adjustability?

I have changed several pots in the past, only to find the problem was downstream, and not the pot itself.

jr

[Chris K]

Originally Posted by jr_tech

I suspect crosstalk between horizontal and vertical circuits...possibly a filter cap on a power supply shared by both is not doing its job. Do you have an oscilloscope?

jr

Yes and service data with waveforms