Total NOOB... I need help with low/crackling right channels..Electrophonic stereo music center

[jake2901]

I just received this combination receiver second hand for free. I realize it might not be an audiophile's dream... but from what I can get out of it the sound is great for my purposes. It is an Electrophonic (Zenith???) stereo music center combination turntable, 8 track, and fm stereo. The left channel seems to work great, but the right channel is very quiet and distorted with crackling. This is true with FM radio or my phone connected through the guitar mic input.. The previous owner had pigtailed all of the speakers to be wired only into the left channel, which is less than ideal. And I would like to get it working properly again.

I have plugged working speakers into the left channel, sounds great...same speaker in the right channel with the volume cranked all the way up it is quiet and very distorted with crackling. This is true no matter which speakers I try. The balance, bass, treble, volume, seem to have no effect in improving the faulty right channel. Just based on reading and research I have come across suggestions such as blown fuses, dirty potentiometers, blown/old capacitors, etc..

My first step was going to be clean the pots with contact cleaner.. Though the inside of the receiver is extremely clean. I also figured I would look for blown fuses. However... I can't seem to find any fuses?!?! I know they must be there, but what I expected to find (a few fuses staring me in the face), I did not. Where are the fuses in this receiver? Can anyone tell based on my images? The close up image is of the backside of the inputs for the right channel. Seems to me these would be the first solder points to check, but I don't really know how to identify a cracked solder, and have very little experience soldering. Any help would be greatly appreciated!! I would like to keep this from going into the landfill, or paying 100$ to get professionally repaired. What are my options?

 

[ryuuoh]

The lack of visible fuses might mean the transformer has an internal fuse.
If you have a DMM, measure the speaker outputs (no speakers connected, volume down) and see what voltages might be there.
If you can, take closer pictures of the circuit board (particularly near the four transistors mounted to the chassis).

 

[jake2901]

The lack of visible fuses might mean the transformer has an internal fuse.
If you have a DMM, measure the speaker outputs (no speakers connected, volume down) and see what voltages might be there.
If you can, take closer pictures of the circuit board (particularly near the four transistors mounted to the chassis).

Hmmm. Can a transformer with an internal fuse go bad and be replaced? If it did blow, would it make sense for low volume and quality to affect only one channel?
I don't have a DMM but I will check the voltage tomorrow. My neighbor should have one. Here are closer images.

 

[jake2901]

So... I got to the point of taking off the volume and balance knobs, etc. And realized my pots did not look like what I expected to see based on other postings on this site and videos on how to clean the pots. I realized they are dual concentric pots. Then, in searching for more information on dual concentric pots, thinking maybe this could be having an effect on the low volume and distortion in one channel and not the other, I came across this thread from last year for a different unit.

http://audiokarma.org/forums/index....-track-down-distortion-in-one-channel.645223/

Could it be that because my unit has dual concentric pots that one channel is affected while the other is not as in this person's case? Is this an expected result from a dirty or worn out dual concentric pot? I'm going to try using contact cleaner for now, to see if there is any improvement.

Edit..
So after cleaning the pots with contact cleaner I notice no difference. I can get the volume to increase in the right channel for a second by switching the function switch from fm stereo to fm and guitar mic, clicking it back and forth, it will play more loudly, but still distorted with crackling for maybe a second before getting quieter again. But cleaning the pots didn't improve anything. Will get a voltmeter on it today.

 

[jake2901]

The lack of visible fuses might mean the transformer has an internal fuse.
If you have a DMM, measure the speaker outputs (no speakers connected, volume down) and see what voltages might be there.
If you can, take closer pictures of the circuit board (particularly near the four transistors mounted to the chassis).

Ok. With the multimeter on the DCV 2000m setting (hopefully I am using this right, I did not get any readings on AC modes), no speakers attached, and the volume all the way down I get a reading of about 100 on the main left, satellite left, and main right and satellite right outputs.

But when I increase the volume to about 50 percent the voltage on the left outputs are 300, right outputs stay at 100.

With volume all the way up, no speakers, left outputs at 1000, right outputs stay at 100. So it seems the right speaker channel is getting power, but there's negligible change in voltage when increasing the volume....?

 

[ryuuoh]

If you slowly rotate the selector switch, does the sound change? You might have a dirty selector switch.
Your unit looks to be using complimentary pairs for the output transistors. I'm guessing it is capacitor coupled, so checking for DC is a bit different. You'll need to connect a resistor to the speaker terminal and measure the voltage. A value around 8~100 ohms should let you see if you have DC at the terminals.