Testing a CTC-11 horizontal hold control

[old_tv_nut]

Originally Posted by Kamakiri

Working backwards in my mind from over a week ago (been a rough week with my wife coming home from rehab), I remember that the oscillator isn't running at all. We checked and re-checked board traces, tube pin continuity, and grounds.

As I understand it, the +275V and the +386V voltages show that everything going into the board is fine. Once again I'm stymied because there are only so many parts here....

In that case, I agree with the hints about sockets. If the plate voltages on the socket are way high (the same as the supplies), it could indicate either that the plate pins aren't connecting (no tube current) or the filament voltage is low (also no tube current). Can you see the filament light up?

[Kamakiri]

Yep, filament is definitely lighting. Tube socket aside for a moment, do you think it would be a waste of time to shotgun the rest of the components on that board?

[old_tv_nut]

Originally Posted by Kamakiri

Yep, filament is definitely lighting. Tube socket aside for a moment, do you think it would be a waste of time to shotgun the rest of the components on that board?

I would measure the voltages on the socket pins first.
[Edit: can you get at the bottom easily? Otherwise, a socket extender can be helpful if you have one.]

[retrogear]

Give us all the voltages on pins of 6CG7 hor osc and afc. You can remove 6DQ5 hor out and the damper tube to measure it

[Kamakiri]

Thanks....give me a day or two and I'll get it back up on the bench. I have to repair my socket extender.....one of the long metal rods pulled right out of the sucker last time I used it

I've been running all of the tests with the 6DQ5 out. To do the diagnosis last time, I had the yoke and convergence board out of the set and plugged into the chassis and everything laid out on the bench so that I could move it around more easily.

[teevee]

Jack Darr did a good writeup about servicing the Synchroguide circuit, if I can find that .pdf I'll post a link..

[DavGoodlin]

Originally Posted by teevee

Jack Darr did a good writeup about servicing the Synchroguide circuit, if I can find that .pdf I'll post a link..

Thanks, that would be great to review as we retreat inside and jump into the weeds on these chassis.

I have 3+ more older RCA's waiting after finishing two CTC16s where tube sockets looked normal but were definitely bad..

[Kamakiri]

Tested resistances. Everything is perfectly in line, except pins 8 and 9. Measured from M1, I get about 8K. Measured from chassis ground, it jumps around (assuming because I'm not using a VTVM) in the range of 40-120 ohms. Should be zero ohms on both.

Since both pins are ground, are we looking at a bad tube socket?

[DavGoodlin]

OK, now jumper to ground pins 8-9 on your test socket and see what it reads, better yet, apply power. Not sure what M1 -is I'm' using the RCA schemo.

[old_tv_nut]

Originally Posted by Kamakiri

Tested resistances. Everything is perfectly in line, except pins 8 and 9. Measured from M1, I get about 8K. Measured from chassis ground, it jumps around (assuming because I'm not using a VTVM) in the range of 40-120 ohms. Should be zero ohms on both.

Since both pins are ground, are we looking at a bad tube socket?

Not sure what M1 is. The pins and the ground trace on the circuit board should all measure zero ohms to chassis ground. VTVM or VOM will not make a difference - a ground pin or PC board trace should be a very low resistance short to chassis ground.

One more thought - make sure your ohmmeter reads a solid zero when you short the leads together.

[Electronic M]

Sam's for the 11 can be found here: http://earlytelevision.org/pdf/rca_ctc11_sams_550_2.pdf

I don't see a M1 on it, but then again I did not take much time to carefully look...

If socket pins, that are shown on the schematic as grounded, measure over an ohm to chassis, then either the ground path is bad, your meter has a problem, or the connection points are dirty. Suspect board to chassis ground connections, traces, and socket in that order.

[Findm-Keepm]

Why M1 (B+ rectifier)? Most resistance readings are taken from Chassis ground - using M1 as a reference for any DC or Ohms measurement will result in odd values - those doubler caps charge and discharge, giving odd values. Clip the negative lead to chassis, and measure to the pins....

Lower left of Page two on the Sams gives the instructions - common negative (Chassis)....

Have you verified the resistances of the ground traces on the board to the chassis - measure the trace, not at the corner eyelets. Those eyelets are 90% of the problems with most RCAs. IIRC, you resoldered those early in the thread.

[Kamakiri]

It's also where many of the resistance tests for that tube are taken from.

[Findm-Keepm]

Pin 8 and 9 to ground should measure close to zero - and you have resistance. Taken from Socket (above) or pins (below), they should both be close to zero.......I'd start there. Runs to the eyelets....simple trace. Assuming the solder connection is good - bigger the blob, better the job does not apply here - go for a clean, shiny fillet.

[Kamakiri]

Cleaned the snot out of the socket and ran my iron over the pins just for good measure. We're now down to 1 ohm, confirmed with both the Snap On meter I always use, and my Jackson Tele-Volter that I rebuilt.

Time to try this again.....