No HV, boost on CTC-22 - Videokarma.org TV - Video

Jon1967us · #1 03-22-2022, 01:29 PM

Having trouble kick starting this thing. Any advice would be appreciated.

Symptom: No high voltage measured and Boosted B+ is too low.

Quick Reference Pics:

Full Schematic: https://drive.google.com/file/d/1Ar9...ew?usp=sharing

Info and Measurements:

• No HV measured
• 280 and 285 B+ rails measure correct
• Voltages on H Osc measure correct
•#Damper diode was bad replaced with NOS
• Waveform on pin 2 of V11 H out looks good, is at correct amplitude. Haven't measured frequency yet, but on the scope it appears to be a little low.
•#Voltage at pin V11, pin 2 appears a little low, at -40 (should be -51)
• Other voltages on V11 appear a little too high - pin 7 =144v, pin 8 = 52v
• Cathode current is very low at 30mA
• Boost voltage only 210v (should be 500)
•#Voltage at H Out anode cap is 140
• Adjustment of H Hold or waveform doesn't improve cathode current or HV
• The Fly is buried deep in the box and I currently can't access for testing for shorts or ringing tests
• H out and HV rect tubes tested and subbed with known and tested NOS ones

I'm wondering if the following caps may have something to do with lack of boost. C80 (.0018 @ 1KV boost), 82 (100pF @ 5KV). What other tests can be done to help to trace to my faulty component?

Yamamaya42 · #2 03-22-2022, 07:32 PM

#Voltage at H Out anode cap is 140

If you mean the plate cap, then this is a MAJOR problem.
With the cap removed, the voltage there should be about the same as what is hooked to the damper, +280 give or take.
+140 is WAY too low.
Question #1 WHY did the damper fail?
Question #2 is the FBT OK and getting the right voltage to run?

You will have to pull things apart and check the main voltage path.

L36 (horizontal efficiency linearity ) L32, L31, and check points 3 to 4 on the FBT, if any of these are bad, it can cause what you are seeing.

Yamamaya42 · #3 03-22-2022, 11:02 PM

From what I can see of the SAMs, L36 , 31 ,32 are easy to get to on the PCB and thus can be resistance checked , and voltage checked, also, if you have voltage (200v ish) on the far side of L31 ( opposite of point 118 ) , you can also do a resistance check from that point on the L31 to the HOT plate cap V11 to HOPE you see about 4.6 ohms as stated on the SAMs, because if you do not... VERY bad news, bad FBT.

Jon1967us · #4 03-22-2022, 11:18 PM

@Yamamaya42

Thanks for weighing in. I took resistances at the points you suggested. L31, 32, 36 don't appear open and measure similar to Sams values.

I did measure between the Damper cathode and the HO plate cap and got around 7Ω. So no opens or shorts here, as well.

Yamamaya42 · #5 03-22-2022, 11:23 PM

Quote:

Originally Posted by Jon1967us

@Yamamaya42

Thanks for weighing in. I took resistances at the points you suggested. L31, 32, 36 don't appear open and measure similar to Sams values.

I did measure between the Damper cathode and the HO plate cap and got around 7Ω. So no opens or shorts here, as well.

with the plate cap off, do you get about 200v at L31?

Jon1967us · #6 03-23-2022, 12:25 AM

Quote:

Originally Posted by Yamamaya42

with the plate cap off, do you get about 200v at L31?

I measure 258 at L31 and the HO plate cap

Tom9589 · #7 03-23-2022, 03:51 AM

Yamamaya42, I saw where a tornado went through your home city yesterday I hope you are doing OK.

Yamamaya42 · #8 03-23-2022, 06:08 AM

Quote:

Originally Posted by Jon1967us

I measure 258 at L31 and the HO plate cap

I was a bit confused by when you said '#Voltage at H Out anode cap is 140 “

That 258v there is normal and enough for it to work.

Next thing to look into is, why did you see a g1 voltage that was 1v too low?
Bad 5GH8A?
These go bad a LOT, you can try to swap with the one in v3 to see if that changes anything if you do not have a spare.

Also, this set dos something weird with the cathode of the HOT and has it wired to the circuit breaker.

You could try to tie it directly to ground for a bit, to see if that makes any difference, the breaker may be bad and not grounding the cathode enough.

Yamamaya42 · #9 03-23-2022, 06:20 AM

Quote:

Originally Posted by Tom9589

Yamamaya42, I saw where a tornado went through you home city yesterday I hope you are doing OK.

We are OK

it was 5 miles away from here.

thanks for asking.

Yamamaya42 · #10 03-23-2022, 10:41 AM

Been looking more closely at the circuit breaker in that set.
First time I have seen a dual setup like that with one pole on the HOT cathode like this.

Hold 1-2 1.3 Amps main bias.
Hold 3-4 .375 Amps HOT cathode. Could be the problem, as mentioned, tie to gnd to see.

Or, the problem may be in the V10 area,

Jon1967us · #11 03-23-2022, 12:16 PM

Quote:

Originally Posted by Yamamaya42

Been looking more closely at the circuit breaker in that set.
First time I have seen a dual setup like that with one pole on the HOT cathode like this.

Hold 1-2 1.3 Amps main bias.
Hold 3-4 .375 Amps HOT cathode. Could be the problem, as mentioned, tie to gnd to see.

Or, the problem may be in the V10 area,

Pin 3 of V11 tests fine to GND.

Good catch on the 140v measured at the HO anode cap. It seems to have jumped back up. Suspecting an intermittent somewhere - cold joint?

Still suspicious of the Fly and will need to test for shorts between pri and sec. If not, there's got to still be an issue in the damper section.

Complete lack of boost and HV says flyback to me. Hope I'm wrong.

Yamamaya42 · #12 03-23-2022, 01:25 PM

It's not unheard of for a FBT to develop poor solder connections from the windings to the solder pins themselves.

Once it starts, it begins a downward spiral due to heat and carbonization.
And from what I understand the FBT does run hot in this.

But if this is the case, it should be easy to fix if one is careful, because there is normally enough healthy winding to re-solder to.
But the FBT has to be removed and looked at closely like under a microscope to see if this is what is going on.

Also, RCA seems to have done things extra weirdly in this set, unlike in the roundies I have seen before, or even the CTC-38, which had a conventional damper tube and Shunt regulator, unlike the SS damper in this and pulse regulator.

The pulse regulator may be a source of trouble, but I doubt it can kill HV completely, from what I can tell, it comes into play after the FBT has been excited and started up, and in this case, it's not getting to that point.

Another thing to look at aside from poor connections on the FBT are the resistors on the output PCB, perhaps some are bad or out of tol and not allowing it to ring up correctly.

zeno · #13 03-23-2022, 02:42 PM

A few notes:
1) dampers were a big problem on these so double check it. Original
was a single diode, first update was two diodes in // newest was
a kind of squarish one.
2) double breaker has a resistor in the cathode. If it gets hot it pops. The breaker has to have its case soldered to the chassis to work. Just
jump it out for now.
3) Never had a bad FBT in one. The big problems were the 5GH8's & other
low level tubes. Also the tube sockets suck.
4) check the hoz hold pot for tin whiskers.

73 Zeno

LFOD !

Yamamaya42 · #14 03-23-2022, 03:16 PM

Quote:

Originally Posted by zeno

A few notes:
1) dampers were a big problem on these so double check it. Original
was a single diode, first update was two diodes in // newest was
a kind of squarish one.
2) double breaker has a resistor in the cathode. If it gets hot it pops. The breaker has to have its case soldered to the chassis to work. Just
jump it out for now.
3) Never had a bad FBT in one. The big problems were the 5GH8's & other
low level tubes. Also the tube sockets suck.
4) check the hoz hold pot for tin whiskers.

73 Zeno

LFOD !

I did not think about the tin whisker possibility, but with that damn metal can around the pots, it can happen it guess.

But I still and very curious as to why he got 140v on the plate cap at one point, then 258v later on, something strange going on there.

But I do agree, ground the cathode for now, get that out of the picture.

Jon1967us · #15 03-23-2022, 03:52 PM

Quote:

Originally Posted by Yamamaya42

It's not unheard of for a FBT to develop poor solder connections from the windings to the solder pins themselves.

Once it starts, it begins a downward spiral due to heat and carbonization.
And from what I understand the FBT does run hot in this.

But if this is the case, it should be easy to fix if one is careful, because there is normally enough healthy winding to re-solder to.
But the FBT has to be removed and looked at closely like under a microscope to see if this is what is going on.

Also, RCA seems to have done things extra weirdly in this set, unlike in the roundies I have seen before, or even the CTC-38, which had a conventional damper tube and Shunt regulator, unlike the SS damper in this and pulse regulator.

The pulse regulator may be a source of trouble, but I doubt it can kill HV completely, from what I can tell, it comes into play after the FBT has been excited and started up, and in this case, it's not getting to that point.

Another thing to look at aside from poor connections on the FBT are the resistors on the output PCB, perhaps some are bad or out of tol and not allowing it to ring up correctly.

Getting HV for the first time for no clear reason. Cathode current is at a nice 180mA. HV at 21.5. I'm not exactly sure what triggered it. Possible there are invisible cold solder joints, a cap woke up, or excess wax buildup I cleaned off on the rectifier anode connection to the Fly.