CTC 10 HV affected by brightness

[old_coot88]

The answer to the Boost voltage question carries some pertinent information.

[JohnCT]

Originally Posted by Turle

Been stuck on this for weeks. Initially I thought it was a focus problem, but The HV on my 10 drops to around 14kv whenever the brightness is up, and it jumps around depending on what’s on screen, I have no idea what could be causing this. I’ve pulled the cap off the regulator tube and it made no difference, the rest of the hv tubes are fine. the power supply seems to be working fine. I even tried a different CRT but it made no difference, does anyone know how I could fix this??

All help is appreciated. Thanks again

I know you said you tried all the tubes, and with that I'm assuming you replaced the HV rectifier in the cage?

I change hundres of those over the years for blooming - it's the number one cause of HV drop when beam current goes up. Try another rectifier.

Does the flyback get hot? A resistance check won't pick up a single shorted turn.

If not, providing the boost voltage as requested will give the group more to go on.

John

[Penthode]

The boost voltage is a most pertinent test. Another common fault is the HV Rectifier. How do you know it is good? Also is there a resistor in series with the HV Rectifier filament? They often go high reducing the filament current to a bare minimum and the low emission will cause the HV to sag.

[miniman82]

You need to run the horizontal oscillator setup procedure outlined in Sams for that chassis. The horizontal circuit is the most finicky of all the circuits in a TV minus perhaps the tuner and IF strip, so if one adjustment is out of whack it will do funny things. Problem is- they're all related so it's difficult to pin down what exactly is causing the problem. When I troubleshoot horizontal circuit issues I do the following:

Begin with HV, is it high enough?

If not, you must figure out why. Possible symptoms include HV pot needs adjusted, shunt tube is dragging down HV which is usually a drifted resistor in it's grid circuit if the pot doesn't get HV high enough, horizontal drive control not set properly (if so equipped, some chassis have one some do not), weak horizontal output tube, weak horizontal oscillator tube.

If you initially have enough HV but you can't get reasonable brightness try rolling rectifier tubes, there can sometimes be a huge difference in how HV responds to various tubes because of their construction, emission and internal resistance. I've taken to installing solid state stick rectifiers in most of my sets, they make HV a bit stiffer.

Lastly if you don't get some improvement, try the horizontal efficiency coil. If it's not set correctly, the circuit can struggle to push enough current through the flyback leading to sluggish performance. Sams will have the steps to follow to set it correctly, just download it and go through it.

[Turle]

Originally Posted by Penthode

The boost voltage is a most pertinent test. Another common fault is the HV Rectifier. How do you know it is good? Also is there a resistor in series with the HV Rectifier filament? They often go high reducing the filament current to a bare minimum and the low emission will cause the HV to sag.

Yes I believe there is a resistor in series with it. I’ll have to check that along with the boost

[Turle]

Originally Posted by Penthode

The boost voltage is a most pertinent test. Another common fault is the HV Rectifier. How do you know it is good? Also is there a resistor in series with the HV Rectifier filament? They often go high reducing the filament current to a bare minimum and the low emission will cause the HV to sag.

The boost voltage seems to be fluctuating with the brightness. Low brightness there’s 660v, high brightness it’s down to 580 I tried a solid state rectifier, nothing.

[Turle]

Originally Posted by miniman82

You need to run the horizontal oscillator setup procedure outlined in Sams for that chassis. The horizontal circuit is the most finicky of all the circuits in a TV minus perhaps the tuner and IF strip, so if one adjustment is out of whack it will do funny things. Problem is- they're all related so it's difficult to pin down what exactly is causing the problem. When I troubleshoot horizontal circuit issues I do the following:

Begin with HV, is it high enough?

If not, you must figure out why. Possible symptoms include HV pot needs adjusted, shunt tube is dragging down HV which is usually a drifted resistor in it's grid circuit if the pot doesn't get HV high enough, horizontal drive control not set properly (if so equipped, some chassis have one some do not), weak horizontal output tube, weak horizontal oscillator tube.


If you initially have enough HV but you can't get reasonable brightness try rolling rectifier tubes, there can sometimes be a huge difference in how HV responds to various tubes because of their construction, emission and internal resistance. I've taken to installing solid state stick rectifiers in most of my sets, they make HV a bit stiffer.

Lastly if you don't get some improvement, try the horizontal efficiency coil. If it's not set correctly, the circuit can struggle to push enough current through the flyback leading to sluggish performance. Sams will have the steps to follow to set it correctly, just download it and go through it.

Okay after messing around with it all night, I’ve came to a possible new clue. When the HV decreases, the horizontal output current increases. Is this an indication of a shorted flyback turn? It doesn’t seem to get very hot

[old_tv_nut]

What is the range of current? Does it go much over 200 mA?

[Turle]

Originally Posted by old_tv_nut

What is the range of current? Does it go much over 200 mA?

Considerably. Close to 250

[old_coot88]

Originally Posted by Turle

Considerably. Close to 250

YEEEE IKES !! (Sound of klaxon) Anything north of 210 is pushing toward redplate/meltdown territory!

[Turle]

Update, I adjusted the crt bias to the minimum and turned up the screens to compensate, it’s much more stable now. Focus is a lot sharper and it’s actually making a half decent b&w picture. The color is very weak though, almost nonexistent. I’ll need to figure out why that is, I messed with the color killer and got nothing.

[miniman82]

Originally Posted by Turle

Okay after messing around with it all night, I’ve came to a possible new clue. When the HV decreases, the horizontal output current increases. Is this an indication of a shorted flyback turn? It doesn’t seem to get very hot

If you had a shorted turn it wouldn’t work at all.

Current goes up because you have a heavy load on it, which is normal. What does “messing around all night” mean? Did you run the setup procedure? Did you verify 1ua cathode current on the shunt tube with a dark screen? Did you null the efficiency coil? Did you verify the double humped waveform with a scope?

You haven’t given us much to help solve your issue...

[Turle]

Originally Posted by miniman82

If you had a shorted turn it wouldn’t work at all.

Current goes up because you have a heavy load on it, which is normal. What does “messing around all night” mean? Did you run the setup procedure? Did you verify 1ua cathode current on the shunt tube with a dark screen? Did you null the efficiency coil? Did you verify the double humped waveform with a scope?

You haven’t given us much to help solve your issue...

I don’t wanna sound like an asshole but I don’t really know what half the stuff is you’re talking about. I don’t have a ton of color set experience

[Electronic M]

Originally Posted by Turle

I don’t wanna sound like an asshole but I don’t really know what half the stuff is you’re talking about. I don’t have a ton of color set experience

Do you have the Sam's or RCA service data for your set? (The Sam's is available for free on the ETFs website if you navigate to early color TV then technical information) The procedures Nick/miniman mentions are standard service adjustment procedures detailed in both of those manuals and are the first things you should do when you experience incorrect horizontal performance.

Nulling the efficiency coil especially should be done to all RCAs that have been brought out of decade long dormancies ...and might be all it needs if you haven't done that yet.

[Kirk]

HV is measured at "0 Beam Current" (black screen) this is when the guns are cutoff. This tells the technician how much HV the system can provide and should be able to reach spec. It is NORMAL for the HV to fluctuate a bit during brightness swings, if its severe- check the setting of the screen and drive controls that they are not too high- also as suggested monitor the boost.

Enjoy!
Kirk