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Trying to repair toshiba six transistor radio

DTiernan

Mar 17, 2021
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I am trying to troubleshoot a 394 toshiba, the volume control is not responsive, it’s just full volume all the time, there is no stations being received. I recapped the dual cap next to the antenna which gave the radio better volume but no signal. Before I replaced the cap I had a very faint signal but no volume. Also the station would not change as I turned the tuner. Any help would be appreciated
Thanks,
Dennis
 

Harald Kapp

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I clarified the title (added radio).

Schematic can be downloaded here.
Check the volume control potentiometer. If the ground pin is loose (either bad solder joint or bad pot), the volume will always be fully on.
Check the variable capacitors for bad solder joints, too. These are responsible for tuning.
In fact, check the whole PCB. Maybe re-soldering all joints may remedy the issues.
 

DTiernan

Mar 17, 2021
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I clarified the title (added radio).

Schematic can be downloaded here.
Check the volume control potentiometer. If the ground pin is loose (either bad solder joint or bad pot), the volume will always be fully on.
Check the variable capacitors for bad solder joints, too. These are responsible for tuning.
In fact, check the whole PCB. Maybe re-soldering all joints may remedy the issues.
Thanks for the suggestions, I did notice that one of the grounding tabs on the variable cap can be push down a little bit, I didn’t know about the potentiometer either, I will check them tonight.
 

DTiernan

Mar 17, 2021
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It seems like the tab on the variable cap that goes to the antenna lead is soldered however the tab is not pressed against the circuit board and there is no trace underneath it , the only connection to this tab is the antenna wire. The leads that go to the volume control appear to be intact. I did measure the voltage going to the base of the converter transistor (2SA52) from the antenna lead. The schematic says it should be 3.1 volts which is what I am getting with my meter. New caps that I soldered in place seem to be alright, but maybe I should double check the polarity of the caps I replaced.
im not sure what direction I should examine next.
 

DTiernan

Mar 17, 2021
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I tried to upload a photo, I was unable. As I was probing the circuit board, I noticed when I put pressure on the third terminal of the tuning cap, I get a station, it was a little loose in the circuit board but the solder connection is good, so maybe there is a break internally in the tuning cap? The first terminal on the tuner can also be pushed down but no change in signal. I have a spare condenser from a similar radio and was thinking to substitute them. Any thoughts would be appreceated. I also wanted to add the only station that comes in is 710 WOR. When I twist the capacitor the station gets weaker.
 

Harald Kapp

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I tried to upload a photo, I was unable.
Resize to 300 kB or less.
it was a little loose in the circuit board but the solder connection is good, so maybe there is a break internally in the tuning cap?
This is a possibility. How did you push? When working on HF circuits usually one needs electrically neutral (non-conductive) tools. Otherwise the added capacity from using e.g. your hands or a screwdriver will change the HF behavior of the circuit.
 
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