panasonic: Panasonic/Matsushita low volume

Hi,

Any pointers on troubleshooting this model. Also need a battery compartment cover if anyone has one.

Thanks,

Charlie

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Hi,

 

Low volume can of course have several causes, like:

1. Wrong power supply voltages. Check the voltages at each stage, starting from the source line to the audio and then to the RF stages.

2. Poor RF sensibility. If (1) is good, first check the IF stages for proper gain and alignment, then for each RF band check for normal local oscillator signal and check alignment (This requires a lab RF signal generator for proper troubleshooting and alignment).

3. Poor audio gain. If (1) is good, then check for faulty stages, from the pre-amp to the output.

 

Using a multimeter, a RF signal generator and an oscilloscope would facilitate the troubleshooting procedure and save time. That said, initially we can just forget about all the above and go for a blind procedure that may fix the issue, based on experience from past similar symptoms. However, a multimeter would facilitate things.

Start by checking the voltages at the transistors.. Audio transistors usually have values closer to the nominal power supply. RF transistors usually run on lower voltages as decoupling RC filters are used that cause some voltage drop thru the series resistor. If a transistor is missing the working voltage, check the RC network (a open resistor or a shorted capacitor), but be aware that some transistors may be just not in use depending on the selected RF band (a schematic diagram would be usefull, otherwise reverse engineering would be required).

Defective electrolytic capacitors are a common cause (due to aging), even if they look fine cosmetically. They tend to fail in several ways, like physically or electrically leaking, dried, much lower capacity than specified, or much higher ESR.

One very common cause for low audio volume is that little electrolytic coupling capacitor that interconnects the volume potentiometer to the first audio pre-amplifier stage. Just replace it with another with similar specification; it does not need to be identical; electrolytic caps value variance is large; just make sure to select a working voltage above the indicated value in the original cap; real capacitamce value may drift 20% below to 50% above the nominal value.

As for the battery cover, 3D print is one solution, as long as one have the time and patience to learn and use such tools. I used the freeware OpenSCAD program to model a stand and a battery cover for my Sony ICF-SW30L and I am in the process of doing the same to print a speaker grille for my Sony WA-8800.

Cheers,

Jose

 

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