Hi everyone, I am currently trying to repair a Grundig radio from the 70's. I found a schematic for this radio here:
https://www.radiomuseum.org/r/grundig_rtv_500.htmlISSUES:- It still seems to work, but the volume slider is extremely sensitive. Putting it at 10% of the sliding range is already too loud.
- I also notice that only the left speaker seems to work, but pressing the 'mono' button makes it play through both, so I won't put too much time in this issue. (But would be nice if this is fixed as well)
INFOAttached you can find the volume control & balance part.
- Top is left channel, bottom is right channel
- R44 & R47 is the balance sliding potentiometer (orange)
- R55 & R56 is the volume sliding potentiometer (green)
OBSERVATIONS/QUESTIONSIt seems that the volume potentiometer has 5 connections for each channel. I do not understand how these are connected inside, I would think that any potentiometer has only three connections (left, right, wiper). Anyone knows where the other connections are for?
When I measure resistance between ground and wiper output of the volume potentiometer (blue arrow), I notice that it rather quickly jumps from 0 to 68K in the first 10% and stays there for other 90% of the sliding range. Does anyone know what could be causing this? I would expect a nice linear increase over the whole range. I do not see any obvious sign of broken caps or resistors.
Let me know if there are things that I should measure etc. I very much appreciate any help!