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 Post subject: very VERY Brown rca not playing audio
PostPosted: Sep Sun 19, 2021 3:29 am 
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Hello there. I got this little turd brown RCA RZA 201T and its currently not playing any sound.At first i thought it wasnt getting any power until i put the speaker right up to my ear and then i could hear a faint speaker hum. turning either dial doesnt alter the hum in any way. anyways after pulling out the guts i decided to replace the old filter capacitor with 2 new electrolytics. one in hopes that it would fix it and two because its probably shot or nearly shot no matter what. anyways unfortunately that didnt fix it and still doing the same thing which the good new is i replaced them correctly. anyone have an idea what it may be? theres 4 more smaller electrolytics that could also be junk....


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 Post subject: Re: very VERY Brown rca not playing audio
PostPosted: Sep Sun 19, 2021 4:42 am 
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If there's an Electrolytic connected to the center tap of the volume control, try replacing that next.

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 Post subject: Re: very VERY Brown rca not playing audio
PostPosted: Sep Sun 19, 2021 5:24 am 
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why yes it looks like there is a 3.3 @ 25 volts there. theres 3 of them all together and one 33 @ 25 volts. since they cheap i will just get some on my next order of caps anyways.


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 Post subject: Re: very VERY Brown rca not playing audio
PostPosted: Sep Sun 19, 2021 7:57 pm 
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well turns out them values are tough to find for sale.... so i thought before i spend forever looking i might as well use a larger capacitor and just try jumping them to see if it changes anything and well.... no nothing changes.....hmmmm


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 Post subject: Re: very VERY Brown rca not playing audio
PostPosted: Sep Sun 19, 2021 9:13 pm 
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Your best bet is to simply change out the four that you had referred to earlier. My suggestion about the one connecting to the VC wiper was because it's a normal troublemaker when it opens.
Replace 3.3 uF with 4.7.

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 Post subject: Re: very VERY Brown rca not playing audio
PostPosted: Sep Sun 19, 2021 9:57 pm 
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The schematic attached below should be pretty close to your set.


3.3µF (microfarad) and 33µF are today's commonly found replacement values.

The Voltage rating of a capacitor is how much juice that it can handle.
This can be increased.

Use 25V or 35V or 50V (I mostly use 50V replacements for these old Mickey Mouse (Voltage) rated capacitors) lol

47µF for the old 50µF
100µF is still a commonly found value today.


The dashed line box on the schematic comprising of C7 C8 and R9 appears to be a three-section Couplate - - this can be replaced with individual components.


Modern day Electrolytics have become...
https://antiqueradios.com/forums/viewto ... 9#p3029559


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 Post subject: Re: very VERY Brown rca not playing audio
PostPosted: Sep Tue 28, 2021 1:39 am 
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well poo..... got order of caps in and so i replaced the one on the volume pot and still nothing but light buzz.so i replaced the other 3 remaining and still same thing..... any more ideas?


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 Post subject: Re: very VERY Brown rca not playing audio
PostPosted: Sep Tue 28, 2021 2:15 am 
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You might want to check the 50000 ohm volume pot and the 300 ohm resister R-17 before the diode. Tom


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 Post subject: Re: very VERY Brown rca not playing audio
PostPosted: Sep Tue 28, 2021 2:36 am 
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the big resistor was the first thing i checked and its good (still is). and i just checked the volume post and it seems to be working as i turn it back and forth.


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 Post subject: Re: very VERY Brown rca not playing audio
PostPosted: Sep Tue 28, 2021 3:37 am 
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Were the transistors checked?

I have two chassis similar, 4 transistor AC radio. Both had at least one transistors gone open. A generic substitute worked for both of the radios. I found my subs in a transistor junk box I have...

GL

Chas.

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 Post subject: Re: very VERY Brown rca not playing audio
PostPosted: Sep Tue 28, 2021 4:20 am 
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Chas wrote:
Were the transistors checked?


That might be the next step after replacing the caps. Use a meter, and carefully, so you don't short anything out, measure, record, and post here each of the three voltage readings you get from each Transistor.

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 Post subject: Re: very VERY Brown rca not playing audio
PostPosted: Sep Tue 28, 2021 4:51 am 
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my multimeter has a diode checking function and so i started check both sides of them and the first 2 were the same on both sides, but the 3rd one i checked (which is crammed down between the transformer, the volume pot, and the filter capacitors) reads nothing on the one side! and i rechecked la few times just to be sure. so that looks like it may be the culprit! (all 3 are c454)


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 Post subject: Re: very VERY Brown rca not playing audio
PostPosted: Sep Tue 28, 2021 4:57 am 
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You need to check them as Transistors, not Diodes.

Put the meter on DC volts, negative lead to circuit ground, and touch the positive probe to each of the three leads, or you can do it on the underside of the PCB, at their specific solder landings.

You are looking for two low voltages very close to each other, and one large voltage on each Transistor.

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 Post subject: Re: very VERY Brown rca not playing audio
PostPosted: Sep Tue 28, 2021 5:19 am 
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ah gotcha. so i went in same order and got .88/15.24/1.36 then the next was .47/15.25/1.16 and then the 3rd one was .00/.05/.03 so i'm still thinking that must be it.


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 Post subject: Re: very VERY Brown rca not playing audio
PostPosted: Sep Tue 28, 2021 9:06 pm 
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I agree. You want to replace that Transistor, and check the values of any associated resistors to it as well.

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 Post subject: Re: very VERY Brown rca not playing audio
PostPosted: Oct Tue 05, 2021 2:40 am 
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well poo again.... changed it out with a new one and no change. but it is showing same thing on the meter as before. so could it very well be one of the 3 resistors near it? any real good way of testing them without removing them as they are a pain to get out let alone put back in.


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 Post subject: Re: very VERY Brown rca not playing audio
PostPosted: Oct Tue 05, 2021 4:20 am 
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Resistors can always be tested in-circuit.

However, if it shows a very low resistance, check to see that it's not parallel to a coil.

Generally 20% tolerance is allowed for 3 band resistors, 10% for a fourth silver band, 5% for a fourth gold band.

One other thing; go over the trace side of the PCB very carefully, using a magnifier if necessary. You are looking to make sure all printed traces are sound and unbroken, and all solder landings look unbroken from the leads soldered to them.

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 Post subject: Re: very VERY Brown rca not playing audio
PostPosted: Oct Tue 05, 2021 6:24 am 
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Radio Demon wrote:
well poo again.... changed it out with a new one and no change. but it is showing same thing on the meter as before. so could it very well be one of the 3 resistors near it? any real good way of testing them without removing them as they are a pain to get out let alone put back in.


You can gently clip one lead on each resistor to get a reading. Then solder back on. It's difficult to get an accurate reading when they're in circuit, though sometimes possible. Usually the meter jumps all over the place.


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 Post subject: Re: very VERY Brown rca not playing audio
PostPosted: Oct Tue 05, 2021 7:00 am 
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Zenith Royal wrote:
It's difficult to get an accurate reading when they're in circuit, though sometimes possible. Usually the meter jumps all over the place.

I've never had that problem.

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 Post subject: Re: very VERY Brown rca not playing audio
PostPosted: Oct Tue 05, 2021 10:08 am 
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Should be noted this set has one side of circuitry connected directly to AC line. Considering compactness, without a isolation transformer, measuring voltages is likely a disaster waiting to happen. This radio has the potential to be at least as dangerous as the tube AA5 almost everyone whines about.

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