Dead, recapped radio - Printable Version
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Dead, recapped radio - lasurveyor - 07-31-2022
I have a Philco 52-944 that I recently re-capped and can’t get a signal out of it. Hopefully someone can give me a tip as to what I’m missing. I may hear a faint crackle or hum in the speaker but no radio signal coming thru. I have checked everything that I could think of, tubes, transformers, tuner, I retraced the schematic, checked continuity throughout the band selector. I even have a 53-958 that I compared wiring. Now here’s the big clue, I replaced the selenium rectifier with a diode and adjusted the following resistor to get the 130v (not what I expected, 15ohm gave me 132v), the 120v called for at the 70mf electrolytic was 116v, but then the voltage at the 3rd electrolytic was only about 40v and the preceding 470 ohm resistor gets blistering hot.
Can you help lead me in some direction?
Thanks,
Alan
RE: Dead, recapped radio - radiorich - 07-31-2022
Hello Alan,
First all that radio looks great so far !
So C38B 40ufd capacitor ?
What i would do with no power applied is to take some resistance readings to make sure there is no shorts and check every tube again it sounds like Audio amp section could where the issue lays it looks like you replaced a lot of resistors and Mica capacitors double check and triple check everything .
Sincerely Richard
RE: Dead, recapped radio - lasurveyor - 07-31-2022
Thanks Richard, the 470 ohm resistor will burn if I don't shut it down. There's a lot of bad or no voltage readings that I don't understand. I think at one point I fed an audio signal into it and got it clear so I don't think the problem is in the output section. What would cause that resistor to burn?
Alan
RE: Dead, recapped radio - radiorich - 08-01-2022
Hello AlaN,
Excessive current draw will cause that resistor to get really hot !
One the first things that I would do is to take a resistance reading but make sure you have no power applied measure the resistance from R26 and C38B junction also check all of your wires go through the schematic and look at everything that is feed from C38B one by one check everything!
Sincerely Richard
462ron - 462ron - 08-01-2022
Hi Alan, just a thought here. If originally the 470 ohm resistor wasn’t burned, then possibly the new 40mfd cap C38b could be bad or you have the + and - reversed, that would surely load down the 110V B+ and overheat that resistor.
Ron
RE: Dead, recapped radio - lasurveyor - 08-01-2022
Thanks Ron, I have checked polarity, but I hadn't thought about swapping out that electrolytic. I'll give it a try. Then I guess I better trace out the schematic, again.
Alan
RE: Dead, recapped radio - radiorich - 08-01-2022
Hello Alan,
That is a good idea what Ron pointed out !
Sincerely Richard
RE: Dead, recapped radio - lasurveyor - 08-01-2022
Swapped out the 38B 40mfd electolytic and the diode too, no change. In process retracing the schematic.
Alan
RE: Dead, recapped radio - RodB - 08-01-2022
Hi Alan,
Check the hot 470 ohm resistor on AM and FM. The 110 volts DC is feeding FM plate circuits as well as audio screens so maybe if it doesn't get hot when AM is selected you can eliminate some circuitry.
RE: Dead, recapped radio - lasurveyor - 08-01-2022
Thanks, haven't thought of that. On AM band I just watched the 470 ohm, 2 watt resistor fade color then the casing began to melt. Not sure about the FM, but I can scratch out any FM circuitry that is isolated by the band selector and reduce the circuitry to look at.
I'm starting to get a feeling about the IF transformers. My trouble started when I damaged Z1 and got a replacement from another radio. Finding the radio dead I replaced Z2 so I had a pair from the loaner 51-934. Their terminals have green and pink dots that don't always agree with the schematic, even one that I never removed. I get good ohm readings so the transformers are probably good, but there may be a wiring problem there. I get a headache if I stare at these too long.
Alan
RE: Dead, recapped radio - radiorich - 08-02-2022
Hello Alan,
I think you may have found your area where the problem lays !
Sincerely Richard