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Old 09-28-2016, 02:54 PM
Crist Rigott Crist Rigott is offline
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Vertical Issues on a Philco 50-T702

Guys,

I've created a problem with my 50-T702. The vertical is squashed on the CRT. Let me explain how this happened.

I obtained a HV module from a member on VK and when I installed it, the HV would only adjust to about 3900 volts, not the 4800 I was looking for. When I disconnected the HV wire, then I could get up to 7200 volts. I'm thinking that something is loading down the module. So here is what I did to trouble shoot the issue.
I disconnected the wire at the junction of the pin 9 of the CRT and the end of the Vert. Centering Pot. I got Good HV on the meter. Reconnected the wire.

Then I disconnected the wire going to R52 from the end of the Horiz. Centering Pot. Again I got good HV. Reconnected the wire.

Then I disconnected the wire going to R57 from the Focus Pot. Again the HV was good. Reconnected the wire.

Then I disconnected the wire going to the Vertical Amp circuits from the junction of R57 and R58. The HV was loaded down a bit but I could still adjust the HV to produce 4800 volts. I then reconnected the wire at the junction of R57 and R58.

The HV could only be adjusted to give the 3900 volts again. It looks like something is loading down the HV in the Vertical Amp section. Now with the high oms resistors R58-R60 connected, they did load down the module some, but not enough that I couldn't adjust the voltage back up to 4800 volts. But with these resistors connected and the Vertical Amp section connected, that's where there is too much of a load on the module.

The whole time I was doing this trouble shooting, I didn't look at the picture so I don't know when the picture collapsed. I've included a picture of what it looks like.

I did a very careful visual inspection of the HV circuit along with the Vertical Amp and the Vertical Osc. sections. I also checked each resistor in all 3 circuits and they checked fine. Unfortunately, I have no way to check the caps in those circuits. Those would be the 6KV ones along with the 1.6KV ones. The problem shows up on another CRT too. I know, but what the heck, I tried it just to be sure. I also swapped out the 7F7 V13, and the 12AU7 V7 but the collapsed problem stayed the same.

So any suggestions as to what I could do to further isolate the collapsed problem? Also any ideas as to what to do about the HV module loading down so much I can't get the voltage up to 4800 volts.

I've included a picture of the problem along with the schematic.

Your help is appreciated. Thanks.

Attached Files
File Type: pdf Vertical Section - 50-T702a compressed.pdf (255.9 KB, 16 views)

Last edited by Crist Rigott; 12-08-2016 at 01:41 AM.
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Old 09-28-2016, 03:01 PM
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Seems pretty likely there's a problem in the vertical amp. V13 gets it's plate voltage from the junction of R57/58. Check C77, R99, R100, R102, R103 etc.
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Old 09-28-2016, 05:37 PM
Crist Rigott Crist Rigott is offline
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Quote:
Originally Posted by bandersen View Post
Seems pretty likely there's a problem in the vertical amp. V13 gets it's plate voltage from the junction of R57/58. Check C77, R99, R100, R102, R103 etc.
Bob,
I carefully checked the plate voltage for V13. I was only getting 12 volts instead of the 235 volts shown in the voltage table. I was only getting 257 volts on pin 6 of V13 instead of the 470 volts listed.

There was no change after substituting C77 and C80. That most likely left the HV caps C81 and C82. C81 was substituted with no change. However the C82 substitution caused the voltages to get very close to the voltage chart. Pin 3 was at 281 volts and pin 6 was at 472 volts.

With the picture adjusted with the Vert. Height and the Vert. Centering controls, it looks pretty good. There is just a hint of foldback at the very top of the picture. It is a little brighter the last 1/32 to 1/16 inch. Over all, pretty good.

However the HV module still refuses to supply more than 3900-4200 volts to the receiver. I'm beginning to think that it is just not capable of doing so. I'm asking those who have used this module on their 50-T702 to confirm that they get 4800 volts delivered to the CRT.

I have some cleaning up of the chassis after all that trouble shooting.

Thanks Bob for taking the time to help me with this problem. It wasn't too many months ago that I did a complete recap and resistor change on this thing. Your help is appreciated. Thank you.

Last edited by Crist Rigott; 09-28-2016 at 10:01 PM.
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Old 09-28-2016, 08:56 PM
tvdude1 tvdude1 is offline
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My 621 had the same problem and many nights on the bench thanks to Chuck A it turned out to be the vertical hold control.
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Old 09-28-2016, 10:00 PM
Crist Rigott Crist Rigott is offline
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Quote:
Originally Posted by tvdude1 View Post
My 621 had the same problem and many nights on the bench thanks to Chuck A it turned out to be the vertical hold control.
We are talking abut the collapsed vertical problem, right?
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Old 09-28-2016, 10:08 PM
Crist Rigott Crist Rigott is offline
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I replaced the HV capacitor and made the repairs from trouble shooting the collapsed issue. It is working well now.

However all I can get out of the HV module is 3900-4000 volts. Anybody?

The HV module I'm talking about is the solid state one that is plugged into the 6V6GT (HV Osc.) socket. Then the HV wire from the module plugs into the 1B3GT socket. Pretty neat the way it works. No more HV collapse. Here is a link on the module:

http://www.myvintagetv.com/philco_hv.htm
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Old 08-12-2017, 11:25 PM
Crist Rigott Crist Rigott is offline
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Well I have a collapsed picture again. I think it was a result of installing a solid state HV supply. When I installed it I was tweaking the voltage pot and it was changing the voltage but my HV meter was in error and was reporting the voltages too low, hence I went pretty high (my guess over the 6KV rating for the caps).

Earlier I had the same problem and replaced C82.

I now have a reliable HV meter so I can adjust the HV to about 4800v.

I clipped in another .0047 6KV cap for a substitute for C82 but that didn't work this time. I did the same thing for C81, C93 and C94.

I measured the voltages on V13 and on pin 3 I get 14V instead of 235V, pin 4 I get -.06V instead of -.6V, pin 5 I get -4.5V instead of .1V, and pin 6 I get 110V instead of 470V.

I get a very good picture and can make all the adjustments but the picture is only about 1/3 to 1/2 high.

In post #1 I attached a schematic of the Vertical section.

I feel I'm chasing my tail on this one. I'm sure once I get this problem licked, I'll have a great little TV with no HV collapse.

Thanks.
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Old 08-13-2017, 12:17 AM
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jr_tech jr_tech is offline
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Is c-77 OK?

jr
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Old 08-13-2017, 08:52 AM
Crist Rigott Crist Rigott is offline
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Quote:
Originally Posted by jr_tech View Post
Is c-77 OK?

jr
Yes. I removed it from the circuit and no change with the picture. Then I substituted it and still no change. I then wired it back in. I also did the same thing for C80.
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Old 08-13-2017, 12:14 PM
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Is the voltage on C 77 around 1200 volts? How about the focus voltage?

jr
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Old 08-13-2017, 06:35 PM
Crist Rigott Crist Rigott is offline
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Quote:
Originally Posted by jr_tech View Post
Is the voltage on C 77 around 1200 volts? How about the focus voltage?

jr
C77= 750V
Focus:
1.5M side=1450V
Center tap=1300V
470K side=825V
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Old 08-13-2017, 06:36 PM
Crist Rigott Crist Rigott is offline
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I forgot to mention that C77 voltage starts out at about 1400V then goes down to 750V about the time the tubes warm up.
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Old 08-13-2017, 06:37 PM
Crist Rigott Crist Rigott is offline
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I also swapped the CRT but no joy. It was something I had to do even though I really didn't think it was the problem.
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Old 08-13-2017, 06:54 PM
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Looking reasonable... have you tried another 7N7?
Does the voltage drop across r-99 match r-102 and r-100 match r-103?
C-5 ok?

jr
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Old 08-13-2017, 07:05 PM
Crist Rigott Crist Rigott is offline
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I also ohmed out the Vertical Amp tube V13. All the resistances were very close to what Sams called out for.
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