GE 821 Horizontal Linearity and Fold Over

[Crist Rigott]

I've been asked to help troubleshoot this problem. I've been assured that every component has been replaced and replaced correctly in the chassis. I'm including a video of what he sent me. The picture has terrible H. Linearity and a H. fold over at about 1/3 of the way from the left hand side.

I asked for voltages and this was what I was given:

Voltages Taken On Tubes V16 and V17 and their SAMS Target Voltages

V16 is Tube 12SN7GT

Pin1 / -9.3 VDC. Should be -1 VDC
Pin2 / 150 VDC. Should be 105 VDC
Pin3 / -0 VDC. Should be -0 VDC
Pin4 / -39 VDC. Should be -25 VDC
Pin5 / 171 VDC. Should be 245 VDC
Pin6 / 0 VDC. Should be .2 VDC
Pin7 / 75 VAC. Should be 85 VAC
Pin8 / 64.6 VAC. Should be 70 VAC

V17 is Tube 19BG6G

Pin1 / -21.6 VDC. Should be -45 VDC
Pin2 / -96.6 VAC. Should be -105 VAC
Pin3 / - 0 VDC. Should be 0 VDC
Pin4 / - 0 VDC. Should be 0 VDC
Pin5 / -22.5 80VP-P. Should be -45 VDC
Pin6 / 270 VDC. Should be 240 VDC
Pin7 / 77 VAC. Should be 85 VAC
Pin8 / 266 VDC. Should be 240 VDC

I was told that the chassis pretty much was good according to the resistance chart.

Here is a link to the video:

https://youtu.be/Idomo6g5fV8

[Notimetolooz]

That's a new one on me.
To help localize the problem, ask him to reverse the yoke horizontal wires, and see if the pattern on the CRT switches left to right. If it does that will eliminate the yoke and CRT as the source of the problem.
I'd like to see the waveform of the current through the yoke on a scope but that might be difficult or risk damaging the scope if care isn't taken. It depends on the circuit. Can that section of the schematic be posted?

[Crist Rigott]

Originally Posted by Notimetolooz

That's a new one on me.
To help localize the problem, ask him to reverse the yoke horizontal wires, and see if the pattern on the CRT switches left to right. If it does that will eliminate the yoke and CRT as the source of the problem.
I'd like to see the waveform of the current through the yoke on a scope but that might be difficult or risk damaging the scope if care isn't taken. It depends on the circuit. Can that section of the schematic be posted?

Switching the yoke wires was tried and the problem switched to the other side of the CRT.

I'll post a schematic.

[old_tv_nut]

What control is being turned in the video?

[Crist Rigott]

Originally Posted by old_tv_nut

What control is being turned in the video?

It has been determined that he's turning the H. Drive and not the H. Lin. control.

[Notimetolooz]

I guess that means R4, which is also labeled Horiz. Lin. Control on that schematic. From the video it seems it does effect the linearity in some fashion.
To bad the SAMS does not show waveforms in that area.
There are many RC combinations in that schematic so it would be a little hard to know where would be good places to look at the waveforms in order to match what is normally seen.
I wonder if there is a special order to adjusting the H. Lin. since there are at least two controls that effect it. They might interact.

[old_coot88]

That's a good use for a source of drive signals, like a B&K Analyst. https://archive.org/details/BKModel1...ge/n7/mode/2up

[old_tv_nut]

Random thoughts (that could be wrong) on how to proceed:
Flyback is OK (?) because the right side of the sweep (H out conducting) looks OK(?)
Left side problem has something to do with damper circuit (?).

--> Investigate effects of adjusting width coil and linearity coil to see if that gives any clue.

Edit: Is damper tube suspect? Triple-check components and wiring connections around damper circuit.

[Crist Rigott]

OK, here's the latest.

The chassis was worked on by somebody decades ago and use it as a training aid. So some of the original components were not there during this latest restoration.

A proper schematic was obtained and the guy is now "restoring" it back to the original according to the schematic.

My guess, is that it will now work when he's done.

Thanks to everybody and their suggestions.

[old_tv_nut]

Originally Posted by Crist Rigott

OK, here's the latest.

The chassis was worked on by somebody decades ago and use it as a training aid. So some of the original components were not there during this latest restoration.

A proper schematic was obtained and the guy is now "restoring" it back to the original according to the schematic.

My guess, is that it will now work when he's done.

Not sure whether to laugh, cry, or just shake my head.

Trying to help when the current condition is not fully described is like the "mechanical nightmare" youtube videos where the customer asks for an oil change after running over a rock and cracking the oilpan.

Best of luck to the guy, and I agree that it will probably work fine when the obvious things are fixed!

[Crist Rigott]

I should have included that the missing parts were some caps on each side of the H. Linearity coil and at least a resistor too.