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 Post subject: Re: Troubleshooting Help - Distortion
PostPosted: Nov Wed 24, 2021 2:35 pm 
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That board isn't same as 6223.

For chassis 63130/131, R29 is on foil side of PCB, my set agrees with photo in Sams TSM-64.

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 Post subject: Re: Troubleshooting Help - Distortion
PostPosted: Nov Wed 24, 2021 5:06 pm 
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Not trying to come across as knowing more (I don't!) then those who are helping in this radio repair, but I am going to throw my .03 cents in. ; )
I asked a question a while back and got no answer. I would like to know just to satisfy my curiosity. Does the distortion at "peak" tuning occur using headphones? Just trying to eliminate an issue with the speaker.
Just based on my limited experience, if I was at this point in trying to figure out the radio's problem, I would get out my magnifying glass and fire up the soldering iron. I would re-flow (and maybe add a bit more solder) to each solder pad on the PCB (start with the solder pads for recently replaced capacitors). I have had radios jump back to life after re-flowing solder, even on untouched factory solder joints. Also, as John mentioned, scrutinize the PCB traces for "breaks". Many times they are very hard to see. If any traces look suspicious, run a jumper wire. You might want to have the radio powered on and tuned to low volume distortion while doing this to hear any changes to audio.
Lastly, the OP mentioned the radio was re-capped a while back and just recently being used again. So the radio was working fine after the re-cap?
One lesson I have learned from radio repair in general is usually the problem ends up being a fairly simple fix. On rare occasion they aren't and you have to dig deeper - all based on my limited experience. I am following this thread and hoping to learn from it.

Jeff


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 Post subject: Re: Troubleshooting Help - Distortion
PostPosted: Nov Wed 24, 2021 5:22 pm 
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Location: Indianapolis, IN
Good question by Jeff as to whether the radio worked properly after re-cap intially ? Jeff---Marty send videos of the problem and even at lower volume, the very severe clipping & distortion was present just at peak of tuning in strong signal. Definitely not speaker.


Now measure E, B, C voltages at X1, the RF-amp transistor shown in earlier SAMS picture.

Notice that the voltages (and differences) progressively decrease as you approach X1---possible the RF-amp transistor is leaky or that C11 (.05 disk cap) is slightly leaky (which is rare but can happen)...

John


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 Post subject: Re: Troubleshooting Help - Distortion
PostPosted: Nov Thu 25, 2021 2:00 am 
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Joined: Nov Mon 26, 2012 1:21 am
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Location: Schererville, IN 46375
This radio never worked properly when I purchased it or after I capped it.

The voltages on X1 (RF AMP) are as follows:

SIG / NO SIG
E: 6.12 / 5.89
B: 5.94 / 5.59
C: 1.7mV / 2mV

X1 crosses to an NTE126. I might have one of those around.

I'm going to check the voltages on the Mixer and Osc, too, just to check.


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 Post subject: Re: Troubleshooting Help - Distortion
PostPosted: Nov Thu 25, 2021 5:37 am 
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Hey Marty, try C11 (.05 disk) first---very easy to change and may be the problem ! Sure won't hurt anything...

John


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 Post subject: Re: Troubleshooting Help - Distortion
PostPosted: Nov Thu 25, 2021 5:51 am 
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Location: Schererville, IN 46375
John,
Strange you tell me that... I just took the cap out of the circuit and the distortion stopped! Of course, the circuit is acting a little funny with tuning, but the distortion stopped. I will have to find a .05uF cap tomorrow and put it in the circuit.

Strange, this is the first time a ceramic cap gave me problems, that I know of. It seemed to always be something more "substantial"... transistor, electrolytic, etc...

I'll report back in the morning... of course, I do have a turkey to get ready tomorrow!

Marty


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 Post subject: Re: Troubleshooting Help - Distortion
PostPosted: Nov Thu 25, 2021 6:03 am 
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Location: Indianapolis, IN
Great !

That's an RF bypass cap, so it makes sense that it would behave oddly with it out of circuit. I've seen a few ceramic disks bad through the years and there are others here that have also.

It sounds as though it'll be fine !

John


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 Post subject: Re: Troubleshooting Help - Distortion
PostPosted: Nov Fri 26, 2021 6:11 am 
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Location: Schererville, IN 46375
Well, it seems like there might be more wrong than the bypass .05 uf cap. I swapped it out with another (.04uf) and still the distortion appears. Leaving it out of the circuit makes it play but with some reception issues.

So, it seems like there is yet another issue going on. I'm going to stop at a local electronics parts store to see if they have Q1 (X1) NTE-126 or equivalent. Maybe see if that is causing these issues.


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 Post subject: Re: Troubleshooting Help - Distortion
PostPosted: Nov Fri 26, 2021 6:52 am 
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Location: Indianapolis, IN
Just sent an e-mail asking you to take the test-point 7 voltages readings again for no/weak & strong signals with the capacitor removed from circuit.

Sounding more as though that transistor may be leaky...

John


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 Post subject: Re: Troubleshooting Help - Distortion
PostPosted: Nov Fri 26, 2021 3:51 pm 
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Location: Schererville, IN 46375
John,
With the capacitor removed, C11 from Sears schematic, with a strong signal, I get 7.09V. Without a signal, tuning off station to no received signal, the voltage is 6.39V.


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 Post subject: Re: Troubleshooting Help - Distortion
PostPosted: Nov Sat 27, 2021 4:33 am 
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Location: Schererville, IN 46375
Problem solved! It was Q1, the RF Amplifier transistor. Must have been leaky because it worked...somewhat. I did replace it this evening and now the radio plays fine and sounds great! No more distortion when tuning to the center of the strong local signals.

Now for an alignment touch-up.

Sure glad I don't charge by the hour! Geesh!

Thanks to all who helped!

Marty


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 Post subject: Re: Troubleshooting Help - Distortion
PostPosted: Nov Sat 27, 2021 5:52 am 
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Location: Indianapolis, IN
Great---sure glad that was it as couldn't think of any other possible cause after all that troubleshooting !

John


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 Post subject: Re: Troubleshooting Help - Distortion
PostPosted: Nov Sat 27, 2021 2:44 pm 
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Image


Send that xistor to me & I'll test it on my state of the art equipment. :wink:

This one is leaky.


Attachments:
GE Transistor Tester 009.JPG
GE Transistor Tester 009.JPG [ 808.42 KiB | Viewed 186 times ]

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 Post subject: Re: Troubleshooting Help - Distortion
PostPosted: Nov Sun 28, 2021 4:50 am 
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Location: Schererville, IN 46375
Wow, Tom, that's an old piece of test equipment! I never saw one of those before. Neat!


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 Post subject: Re: Troubleshooting Help - Distortion
PostPosted: Nov Sun 28, 2021 6:07 pm 
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They pop up on ebay every once in awhile... I bought it as a nostalgia piece, but it does work fairly well for ger transistors. Unless shorted, a Silicon will show no leakage & gain is usually full scale.

Testing gain.. Transistors from a TR-1 would barely move the needle.


Attachments:
GE Transistor Tester 008.JPG
GE Transistor Tester 008.JPG [ 783.09 KiB | Viewed 137 times ]

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