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 Post subject: Re: 1955 Zenith TV No Sound
PostPosted: Jan Sat 06, 2018 1:25 pm 
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Joined: Feb Mon 27, 2017 4:53 am
Posts: 45
Location: Chicago
Thanks for the feedback. In my testing, I did not have the CRT connected to try to isolate that as part of/not part of the problem. All other connections were made appropriately.

So far, the two things that I'll check are the 12AX7 and the unintended burnt solder/flux conducting issue. I can totally see that this might be since I'm made so many checks and changes to the caps and resistors trying to identify the issue.

I'm in Germany for another week, but will get to it next weekend and report back!

cheers,

craig.


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 Post subject: Re: 1955 Zenith TV No Sound
PostPosted: Jan Sat 06, 2018 6:48 pm 
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Joined: Nov Thu 11, 2010 6:03 pm
Posts: 664
Location: Pewaukee, WI
irob2345 wrote:
Sorry! Didn't read the whole story! To me, a 12AX7 is a valve, not a tube! A CRT is a tube!


I'm guessing you're not from the USA...This forum is USA based so to most folks here THIS is what we picture when a valve is mentioned. :P

Image

And this is what we think of as a tube/vacuum tube.
Image

Also, there is no such thing as line and frame oscillators; Only horizontal and vertical (otherwise what would the Outerlimits introduction control? :mrgreen: ).

By reading this you have now passed the first course of American TV english 101.


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 Post subject: Re: 1955 Zenith TV No Sound
PostPosted: Feb Sun 04, 2018 2:44 am 
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Joined: Feb Mon 27, 2017 4:53 am
Posts: 45
Location: Chicago
Ok. Have made some progress and feel that I am at the make or break point.

After a number of sessions looking over the circuits and validating my work, I now have the negative voltage problem resolved (don't ask) and have all the correct voltages going through the cable to the picture tube. See below:

Image

My voltages are as follows:

Pin - Target V - Measured V
-------------------------------
12 --- 6.3 VAC --- 6.5 VAC
11 ---- 50 ---- 30 to 130 (variable resistor directly impacts)
10 ---- 340 ----- 310
1 ------ 0 -------- 0
2 ------ 25 ------- 26

The problem that I have is that there is no light appearing in the picture tube. No fuzz, no nothing.

Reiterating what happened was I bought the tv with no picture signal, recapped a few of the electrolytics, got a picture. Wanted to then recap the entire thing, but after 10 minutes of trying to dial in the picture, the tube quickly started getting dark so I turned the tv off. The picture shrunk to a single point on the screen and slowly went away.

I have spent the last year recapping and checking resistors and now finally have the correct voltages going to the tube, but no light.

I know that the picture tube *did* work. What can I test or look for to identify if the picture tube is dead or not?

Thank you all for your help so far!

craig


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 Post subject: Re: 1955 Zenith TV No Sound
PostPosted: Feb Sun 04, 2018 8:25 pm 
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Joined: May Thu 14, 2015 4:15 pm
Posts: 633
Location: Dallas, TX
Maybe the high voltage died. Check to see if the horizontal output is working. Lately my favorite way of doing
a quick check is to hold a compact fluorescent bulb near the horizontal output tube, the flyback or even the yoke
wires. If it lights your good. Another way is to see if you can draw an arc (about 1/4 inch) with a grounded screwdriver
from the high voltage tube top cap. Careful you don't get zapped with that one.

_________________
Tim
"Excellent!" I cried. "Elementary," said he. - Sherlock Holmes


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 Post subject: Re: 1955 Zenith TV No Sound
PostPosted: Feb Sun 04, 2018 10:25 pm 
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Joined: May Sun 07, 2017 11:35 am
Posts: 151
Yes check the HV. Your voltages look OK, but G2 a bit low points to low B+boost which in turn could mean a problem with the flyback. A shorted turn in the overwind would shut down your HV.

But before we go there:

Is the CRT heater lit?

Is the CRT good?

Check it with this method:

viewtopic.php?f=3&t=331576


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 Post subject: Re: 1955 Zenith TV No Sound
PostPosted: Feb Mon 05, 2018 12:36 am 
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Joined: May Thu 14, 2015 4:15 pm
Posts: 633
Location: Dallas, TX
The CRT was working.
The fluorescent bulb doesn't even have to be a working one. Keep one in your tool box.
Attachment:
FluourHorzE01.jpg
FluourHorzE01.jpg [ 86.3 KiB | Viewed 160 times ]

If it lights then the horizontal output is running. The HV rectifier could be bad in that case or the frequency could
be way off or something else.

_________________
Tim
"Excellent!" I cried. "Elementary," said he. - Sherlock Holmes


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 Post subject: Re: 1955 Zenith TV No Sound
PostPosted: Feb Tue 06, 2018 9:32 am 
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Joined: Jun Thu 25, 2015 3:21 am
Posts: 1225
buy the hv probe for your vtvm or alternatively a stand alone hv probe and check the hv. clip the ground lead to the chassis and slip the tip of the positive probe lead under the rubber cap for the second annode. that will tell you what your hv is. if it matches what the schematic calls out for the hv for your set then you have a bad crt or a bad connection between the crt second annode and the hv lead. if the hv is low or nonexistent then more troubleshooting is required in the hv circuits. do not use the normal probe for your vtvm.

i would also check the circuit that is supposed to be 50 volts but reads 30 volts. you mentioned a variable resistor in that circuit that changes the voltage. when adjusting it does the voltage ever get near 50 volts?

remember all voltages are + - 20 percent unless otherwise noted in the service notes.


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 Post subject: Re: 1955 Zenith TV No Sound
PostPosted: Feb Tue 06, 2018 5:13 pm 
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Joined: Jan Mon 04, 2010 2:52 am
Posts: 2310
With any vintage CRT set including your 1955 Zenith black and white console, I wouldn't have spent a dime towards the repair unless the CRT was checked out good using a CRT tester.


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