Grundig 5299: Right channel volume lower than left channel

 I tried to balance by adjusting the "Balance Stereo" knob but that did not have any significant change to the volume of the right channel.  The volume of the left channel is significantly louder then the right channel in FM with a decoder, Tape and Phono input and in Stereo or Mono.  I replaced all paper capacitors.  I suspect the R1 (2x500 ohms) resistor which is the volume potentiometer or the right channel output transformer has gone bad.  How do I test the R1resistor and the output transformers? I do have the schematic (Howard Sam Photofact) and but it does not illustrate the R1 resistor or the output transformer in the schematic.  Please advice.

To thank the Author because you find the post helpful or well done.

I suggest that you supply a signal from a tone generator (i. e. 1 kHz sine, 200 mV) to both channels of the tape input. Set tone and balance controls to mid position and adjust volume to a suitable level without clipping. Then, compare the signal levels at corresponding nodes of left and right channel amplifiers (measure with an oscilloscope, if possible) to find out where there are differences. Also, you could check the DC voltages at the valves to see if anything is abnormal (specifically, look for positive voltage at the control grids, that is a sign of leaky coupling capacitors). Note that the phase split valve has its grid leak connected to the cathode instead of ground, so in that case you have to measure the voltage across the grid leak instead of from grid to ground.

Output transformer failures are very seldom. If you want to test the transformers, first measure the DC resistances of all windings of both transformers and note any large differences (typically, ± 20 % is acceptable). To find out if there are shorted turns or a problem with the core, disconnect anything in the circuitry that might load the transformer (as far as i can see from the schematic, it is only the negative feedback network). Then, unless you have access to a good LCR meter, supply a 1 kHz sine signal of a few volts RMS from a tone generator to one speaker output of the radio, via a variable resistor. Connect two multimeters set for AC volts, one across the speaker output and one across the resistor. Adjust the resistor to get the same reading on both multimeters. Then repeat on the other speaker output and see that you get the same result. Maybe it could be a good idea to repeat at other frequencies (i. e. 100 Hz and 10 kHz) too.

To thank the Author because you find the post helpful or well done.

Thank you Torbjorn Forsman for your hints.  With your advice I checked the inverter tube and it was in good order.  Then I checked the AF amp tube ECC83.   I was able to trace a bad coupling capacitor 0.001uF (C118 in the Sam Photofact manual) at the pin 3 of the preamp tube ECC83 (V8) leading to the speaker coil. The 6.8kOhm coupling resister was fine so I left it alone.  I am glad I did not have to replace the volume pot or the transformer.  Again, thank you for your kind advice.

To thank the Author because you find the post helpful or well done.