21-CT-55 power supply failure

[miniman82]

I took a bunch of readings tonight, all done with an live picture on the screen and all circuits functioning.

Pin 3 of the ballast is a 430 ohm resistor, which feeds all 285v circuits that are not IF/tuner related. The voltage drop accross it is 96 volts, which according to ohms law means it's dissipating 21 watts. Inserting the current meter indicated that the circuits are drawing about 88ma from that pin.

Pin 2 of the ballast is an 800 ohm resistor, feeding IF/tuner. Voltage accross it is 70 volts, indicating a 6 watt dissipation. The circuits of this leg only draw 34ma, but that makes sense to me since there are a lot more plates to feed on the other leg.

Horizontal is still goofy. Something has GOT to be causing the HOT to draw excessive current, but I cannot figure out what it is. The loaded down horizontal section has got to be what's causing all the other issues, it's the only thing in common with every part of the set. Whatever it is, it doesn't seem to be affecting HV though.

[Kevin Kuehn]

You could always try adding a 100 ohm 10 watt cathode resistor on the HOT, just to see how much the current drops, and to what effect it has on the other symtoms. Is there any possibility there is leakage between the HOT socket pins?

[Penthode]

Originally Posted by miniman82

Horizontal is still goofy. Something has GOT to be causing the HOT to draw excessive current, but I cannot figure out what it is. The loaded down horizontal section has got to be what's causing all the other issues, it's the only thing in common with every part of the set. Whatever it is, it doesn't seem to be affecting HV though.

Excessive horizontal output tube current can be due to a number of things. Is the horizontal drive correct? Excessive drive will cause excessive current.

What are the voltages around the tube? What does the horontal linearity look like? Depending how the linearity looks, that will provide a clue(s). How about a picture of a crosshatch pattern on the screen?

Have you checked and substituted the H O Tube? (Sorry, HOT to me means horizontal output transformer not tube). It could be gassy.

I am curious you say the EHT (+25,000v) is okay. How much curent is the 6BK4 shunt regulator drawing? It could be the EHT is low or high depending on the shunt current. Without the shunt, the EHT voltage should jump to +35000 to +40000. (Reminds me of the time my Grandma was watching her CTC11 and the shunt tube was bad. Her cat would like to sleep on the top of the set and she wondered why the cats hairs stood out. The EHT with my divider probe and VTVM measured +40000V. I suppose the cat had an especially good dose of Xrays when passing in front of the screen!

Terry

[miniman82]

Originally Posted by Penthode

Excessive horizontal output tube current can be due to a number of things. Is the horizontal drive correct? Excessive drive will cause excessive current.

Drive is excessive, but I can't figure out why. I can't even get the drive lines to go away with the control and the oscillator tube has incorrect grid voltage as well, not sure where to go with this.

What are the voltages around the tube? What does the horontal linearity look like? Depending how the linearity looks, that will provide a clue(s). How about a picture of a crosshatch pattern on the screen?

Lin is fine, nothing amiss there.

Have you checked and substituted the H O Tube?

2 different ones, it's not the tube.

I am curious you say the EHT (+25,000v) is okay. How much curent is the 6BK4 shunt regulator drawing?

Don't know, when Wayne was here we checked the HV and it was fine. If the shunt were set incorrectly, I would expect it to be much higher, or if it were redplating much lower.

[Penthode]

Originally Posted by miniman82

Drive is excessive, but I can't figure out why. I can't even get the drive lines to go away with the control and the oscillator tube has incorrect grid voltage as well, not sure where to go with this.

Since we can assume the oscillator is on frequency, have you set up the synchroguide with the horizontal locking range as per the service info?

Is the horizontal waveform amplitude applied to the grid of the 6CB5 correct?
Have you replaced C232 (0.01ufd)?

Does the horizontal drive control work properly eg do you see a change in the picture?

Lin is fine, nothing amiss there.

Are you sure they are drive lines? (I am suspicious because drive lines = bad linearity and you said the linearity is okay). If you rotate the horz hold so the picture moves to the right, do the lines remain stationary (drive lines) or do they move opposite to the picture movement (retrace line image)?

Don't know, when Wayne was here we checked the HV and it was fine. If the shunt were set incorrectly, I would expect it to be much higher, or if it were red plating much lower.

I was wondering if the HV reserve is there. I guess if you are getting lots of drive, the HV is okay. But if the brightness is advanced, does the picture bloom or does the width increase? (This would indicate the regulator is dropping out of regulation and the HV being generated is insufficient).

[miniman82]

Originally Posted by Penthode

Since we can assume the oscillator is on frequency, have you set up the synchroguide with the horizontal locking range as per the service info?

Yep, everything is set up right and I have equal peaks on the wave coil.

Is the horizontal waveform amplitude applied to the grid of the 6CB5 correct?

Yes, but the waveform has a flat top.

Have you replaced C232 (0.01ufd)?

First thing I did.

Does the horizontal drive control work properly eg do you see a change in the picture?

It works, but because the oscillator is making such a large waveform it doesn't get rid of the drive lines.

Are you sure they are drive lines? (I am suspicious because drive lines = bad linearity and you said the linearity is okay). If you rotate the horz hold so the picture moves to the right, do the lines remain stationary (drive lines) or do they move opposite to the picture movement (retrace line image)?

The line moves opposite of the picture. That means it's not a drive thing?

I was wondering if the HV reserve is there. I guess if you are getting lots of drive, the HV is okay. But if the brightness is advanced, does the picture bloom or does the width increase? (This would indicate the regulator is dropping out of regulation and the HV being generated is insufficient).

No blooming, seems to have plenty of brightness. BTW, Wayne is probably right about the picture. It seems to be noise, not hum or anything else.

[Penthode]

Originally Posted by miniman82

The line moves opposite of the picture. That means it's not a drive thing?

Yes, that means that either the retrace is a bit slow or the CRT is not blanked off during retrace. It isn't a drive line that you see.

The one white line is probably a video overshoot meaning that the perhaps a sync pulse edge is causing the line on retrace. The multiple lines to the left of it are the individual cycles of burst. The overshoot will generally be due to IF alignment or if the fine tuning moves the video carrier too far down the Nyquist slope. Do you see the line with the video injected at baseband?

I have seen the line made more obvious if the CRT RGB screen adjustments are set too high: they have to be set to ensure the beam current extinguishes on retrace.

No blooming, seems to have plenty of brightness. BTW, Wayne is probably right about the picture. It seems to be noise, not hum or anything else.

Then that sounds okay to me. If it is picked up at the receiver front end, could it be your workshop fluorescent light?

[miniman82]

Since it's not a vertical blanking issue, how exactly does this chassis blank horizontally? I don't see a blanking tube.