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Old 20th May 2022, 9:34 am   #1
danmih83
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Default Sanyo RP1250 - volume control problem

Hello,
I have bought this nice design radio which has a problem: it plays very loud at minimum volume (right after the click of the pot). The volume turns even louder towards the end of its travel.

I have tried with another potentiometer, the problem is the same.
There are no PCB problems (missing the grounding of the potentiometer would have created a similar problem).

I suppose the input signal is very high, but I have no idea how to turn it down.
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Last edited by Cobaltblue; 20th May 2022 at 9:38 am. Reason: circuit removed Rule B8
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Old 20th May 2022, 5:33 pm   #2
agardiner
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Default Re: Sanyo RP1250 - volume control problem

An odd one. The circuit is pretty standard for a pocket set, so I would not expect this. First thoughts is the potentiometer or ground, but you have already eliminated this.

Is the sound clear, or does it distort? It would seem like a fault to me rather than a design issue, but you could always add a shunt resistor between the wiper of the pot and ground to reduce the overall level.
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Old 20th May 2022, 5:36 pm   #3
Cobaltblue
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Default Re: Sanyo RP1250 - volume control problem

I was wondering if there is a crack in the pcb effectively removing the connection to the bottom end of the volume control.

Cracks in PCBs are reasonably common as these little sets get dropped a lot.

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Old 20th May 2022, 6:19 pm   #4
danmih83
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Default Re: Sanyo RP1250 - volume control problem

Thank you for your replies.
I will check again for cracks, but the GND track of the potentiometer is covered with a thick layer of solder.

Eventually I will add a resistor, but I was curious why this problem appeared. I don't think it came like this from the factory.
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Old 28th May 2022, 11:11 am   #5
danmih83
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Default Re: Sanyo RP1250 - volume control problem

Eventually i will add a resistor because I can't figure it out. It might have been a problem from the AGC, but i can't figure where, the diode is ok. I don't think the capacitors or resistors have lost their values. The IF transformers have not been touched
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Old 28th May 2022, 8:36 pm   #6
roffe
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Default Re: Sanyo RP1250 - volume control problem

On this radio the potentiometer is grounded to a short PCB track-only a couple of centimeters long.This ground track is in turn grounded to the rest of the radio through a wire.If this wire is badly soldered or cut off,you could very well get this problem.
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