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 Post subject: Help me diagnose a problem with my 1950 Capehart Farnsworth
PostPosted: Aug Mon 30, 2021 4:37 am 
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I replaced all the capacitors before i powered it up, when The recap was finished I powered it on and the 5U4 blew up, please help


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 Post subject: Re: Help me diagnose a problem with my 1950 Capehart Farnswo
PostPosted: Aug Mon 30, 2021 6:28 am 
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Location: DĂĽsseldorf/Germany
Hi,
Sounds like you didn´t change the elythics of the power supply (As far you made no mistake in your wiring!).
Check them for shorts, but just because of the age it will better,
to use new ones.
Advice: Add a securit braker to save the 5U4!

Regards,
SIXMILLION DOLLARMAN

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ScottyBeamMeUpThereIsNo 4/3-TV/AM OnEarth


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 Post subject: Re: Help me diagnose a problem with my 1950 Capehart Farnswo
PostPosted: Aug Mon 30, 2021 12:10 pm 
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Almost certainly a short. Check that the filter capacitors are not in backwards.


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 Post subject: Re: Help me diagnose a problem with my 1950 Capehart Farnswo
PostPosted: Aug Mon 30, 2021 12:38 pm 
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Location: 13 Critchley Avenue, PO Box 36, Monteith Ont, P0K 1P0
Ben haley wrote:
I replaced all the capacitors before i powered it up, when The recap was finished I powered it on and the 5U4 blew up, please help


Do you have, and if you do did you follow a schematic while replacing the capacitors to verify values and locations?

As Scott said, there is likely a short somewhere, and I'd guess it's most likely due to an incorrect polarity or placement on the Electrolytic Capacitor(s) in the power supply.

Find a schematic and compare your work to the schematic.

(Next time ..... ignore the wholesale recapper advice, do some sensible testing first, then replace your parts only one or two at a time until you get a feel for the process and the circuits).

cheers


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 Post subject: Re: Help me diagnose a problem with my 1950 Capehart Farnswo
PostPosted: Aug Mon 30, 2021 7:01 pm 
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I replaced every cap in the set including the Electrolytic caps, I removed the old ones from the Circuit and put the new ones on the bottom I don’t have a schematic to look at, I went through everything to make sure no leads were touching, also can anyone tell me if film caps have polarity or not?


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 Post subject: Re: Help me diagnose a problem with my 1950 Capehart Farnswo
PostPosted: Aug Mon 30, 2021 9:00 pm 
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Location: Woodinville, WA USA
Film caps do not have polarity. This article has info about identifying and replacing caps in old TVs and radios:

https://antiqueradio.org/recap.htm

What is your TV's model number? This page at the Early TV museum website has a number of Capehart-Farnsworth TV service manuals:

http://www.earlytelevision.org/tv_schem ... l#capehart

I have a 1948 model 661-P Capehart-Farnsworth set, one of my favorite TVs. This article describes how I restored it:

https://antiqueradio.org/CapehartFarnsw ... vision.htm

The article also includes a little biographical info about Homer Capehart and Philo Farnsworth -- both interesting characters.

I agree with others that electrolytic capacitors in your power supply would be an obvious thing to check. And when you have replaced many parts en masse without trying out the set, it is prudent to re-check all of your work, in case you accidentally created a short circuit by dropping a blob of solder somewhere, etc. If you get your hands on a schematic, this double-checking will be easier to do.

Regards,

Phil Nelson
Phil's Old Radios
https://antiqueradio.org/index.html

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 Post subject: Re: Help me diagnose a problem with my 1950 Capehart Farnswo
PostPosted: Aug Mon 30, 2021 10:58 pm 
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Location: Lafayette, CO
Okay, so you have a shorted B+. We can only guess where it is. Easy to jump on electrolytic replacement. The only way to find it is to systematically remove loads to isolate the area. I like calling that game 'Where's Waldo?'. It's in there somewhere. Oh, and only remove one load at a time. Craig


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 Post subject: Re: Help me diagnose a problem with my 1950 Capehart Farnswo
PostPosted: Aug Tue 31, 2021 4:34 am 
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+1, Craig.

Reminds me of an incident today. I got a 30W laser (with the board mounted to it) that had a dead short. I couldn't find the bugger anywhere on the PCB. I decided to do a trial by fire. Sometimes the transformer coil (Only 1. The board is basically a Switched power supply running at 100MHz) shorts, or the transistor has infantile postmortem shorting syndrome. I pushed 50 amps through that thing, at 6V (it would be 48 without a shout, but a little bit of resistance brought it down to that point). Sure, the wires to the laser got hot. Sure, part of the board was baked (slightly browned). SURE nothing blew up. At that point, I replaced the transistor and transformer. No Bueno. I just said "screw it" and replaced the whole damn board. Worked fine after that. Manufacturer defect. Nice.

But the good thing, is that it (your TV) is much easier to service than surface mount PCB crap.

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 Post subject: Re: Help me diagnose a problem with my 1950 Capehart Farnswo
PostPosted: Aug Tue 31, 2021 2:43 pm 
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With an ohmmeter, start checking for a short at the filament of the 5U4, pins 2 and 8, If you measure a low resistance, follow it through the B+ lines until you find it.

Post the model number, and one of us may have the schematic. Also, check with the ETF site; they may already have a scan of the service data.

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 Post subject: Re: Help me diagnose a problem with my 1950 Capehart Farnswo
PostPosted: Aug Tue 31, 2021 3:46 pm 
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Tim Tress wrote:
With an ohmmeter, start checking for a short at the filament of the 5U4, pins 2 and 8, If you measure a low resistance, follow it through the B+ lines until you find it.

Post the model number, and one of us may have the schematic. Also, check with the ETF site; they may already have a scan of the service data.


To be clearer: measurement should be taken between pin 2 ( or 8 ) ,of the 5U4 and chassis ground.
Any value lower than a few kilohms should be considered as suspect. A reversed (backward connected) polarity filter cap won't be detected by this test but can also kill the rectifier tube (as well as the reversed cap)
If everything looks OK it could also be a defective 5U4 tube.
For further tests under power It is recommended to install a temporary protection device (small wattage resistors in the plate circuits of the rectifier tube, or a fuse in the b+ return circuit gnd) to protect the 5U4 tube (and power transformer) against heavy overloads or shorts.


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 Post subject: Re: Help me diagnose a problem with my 1950 Capehart Farnswo
PostPosted: Sep Mon 06, 2021 9:39 pm 
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I can’t do it without a schematic, the model is a 3012M


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 Post subject: Re: Help me diagnose a problem with my 1950 Capehart Farnswo
PostPosted: Sep Mon 06, 2021 9:51 pm 
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Location: 13 Critchley Avenue, PO Box 36, Monteith Ont, P0K 1P0
Ben haley wrote:
I can’t do it without a schematic, the model is a 3012M


Is this correct ? It's not super clear as far as the titles on the pages ::

https://www.earlytelevision.org/pdf/hof ... 7a-6-7.pdf

Or :

http://www.segalandassociates.com/Docum ... 951-TV.pdf


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 Post subject: Re: Help me diagnose a problem with my 1950 Capehart Farnswo
PostPosted: Sep Mon 06, 2021 10:16 pm 
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John Bartley wrote:
http://www.segalandassociates.com/Documents/Radios-Televisions/Beitmans/Beitman-1951-TV.pdf
CX-33 chassis starting at page 24.

Curtis Eickerman

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 Post subject: Re: Help me diagnose a problem with my 1950 Capehart Farnswo
PostPosted: Sep Tue 07, 2021 12:16 am 
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Joined: Apr Sat 06, 2013 2:18 pm
Posts: 668
Location: New Hampshire
Dittos John. Nobody, especially someone new should ever do a wholesale recap.
Take things one stage at a time. Power supply then get a raster (HV) & at that point you
will KNOW the CRT, FBT & yoke condition. I do have a basket of tomatoes if anyone wants to throw
them at me, this is a real touchy subject. I will stand by it.

73 Zeno 8)
LFOD !

John Bartley wrote:
Ben haley wrote:
I replaced all the capacitors before i powered it up, when The recap was finished I powered it on and the 5U4 blew up, please help


Do you have, and if you do did you follow a schematic while replacing the capacitors to verify values and locations?

As Scott said, there is likely a short somewhere, and I'd guess it's most likely due to an incorrect polarity or placement on the Electrolytic Capacitor(s) in the power supply.

Find a schematic and compare your work to the schematic.

(Next time ..... ignore the wholesale recapper advice, do some sensible testing first, then replace your parts only one or two at a time until you get a feel for the process and the circuits).

cheers


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 Post subject: Re: Help me diagnose a problem with my 1950 Capehart Farnswo
PostPosted: Sep Tue 07, 2021 1:50 am 
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Joined: Aug Mon 30, 2021 4:26 am
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The CX-33 chassis doesn’t look the same because I don’t see the 4 section filter cap in the power supply, it has a 3 section, 2 section, and a single section. My tv has a 4, a 3 and a 2 section


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 Post subject: Re: Help me diagnose a problem with my 1950 Capehart Farnswo
PostPosted: Sep Tue 07, 2021 1:51 am 
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Joined: Aug Mon 30, 2021 4:26 am
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But the knob chart looks the same


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 Post subject: Re: Help me diagnose a problem with my 1950 Capehart Farnswo
PostPosted: Sep Tue 07, 2021 1:53 am 
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Joined: Aug Mon 30, 2021 4:26 am
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Funny thing is I can’t find a chassis number


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 Post subject: Re: Help me diagnose a problem with my 1950 Capehart Farnswo
PostPosted: Sep Tue 07, 2021 1:57 am 
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Location: 13 Critchley Avenue, PO Box 36, Monteith Ont, P0K 1P0
Ben haley wrote:
The CX-33 chassis doesn’t look the same because I don’t see the 4 section filter cap in the power supply, it has a 3 section, 2 section, and a single section. My tv has a 4, a 3 and a 2 section

In the schematic, the first cap, the three section, is technically a two section because the first two 40UF are paralleled to make one 80UF cap.
How are yours actually wired?


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 Post subject: Re: Help me diagnose a problem with my 1950 Capehart Farnswo
PostPosted: Sep Tue 07, 2021 2:07 am 
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Mine definitely has 4 values in the 4 section


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 Post subject: Re: Help me diagnose a problem with my 1950 Capehart Farnswo
PostPosted: Sep Tue 07, 2021 2:13 am 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: 13 Critchley Avenue, PO Box 36, Monteith Ont, P0K 1P0
Ben haley wrote:
Mine definitely has 4 values in the 4 section

That may be, but how are the four sections wired? If any of them are paralleled, as is shown in the schematic, it may have been done previously in order to get to the correct values.


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