Lasonic TRC-931- No stereo sound on Tuner function only

[Myklejay]

I have a Lasonic TRC-931 (MKII) that works well, except for no STEREO sound while using the RADIO function. I'm not hearing any scratchy pots or switches.

1) When RADIO function is selected, with STEREO selected, i only have sound in the left channel, with very low (almost non-existent) sound in the right channel with the volume turned up, balance works.
2) When RADIO function is selected, but with MONO selected, I get sound on both left and right channels at equal volume, and balance works.
3) When the AM/FM switch is rocked back and fourth several times quickly, the FM sound becomes very distorted on the left channel when STEREO is selected. The distortion goes away when switched to MONO. (makes me think that this AM/FM selector switch may be the culprit)
4) I have perfect STEREO and 2 channel MONO sound with all other functions on the box. (tape, phono, aux)
6) When headphones are plugged in, I get the same symptoms as playing through the speakers (no stereo sound with RADIO function, all other functions have STERO sound)
7) The box also has a ground type buzz that gets louder when the volume knob, or anything metallic on the left side of the box is touched. Crazy thing is, when the A tape deck EJECT button is touched, the buzz goes away completely...(not sure if the two issues are connected or not)

I have taken all boards out, looked them over for anything obvious, and have thoroughly cleaned out all pots and switches with Deoxit D5. This did not help the issues noted above.

Any suggestions to help sort out these issues would be greatly appreciated!

 

[hopey]

Great explanation of your problems, too many times I hear how good Deoxit is. This is an example were the contacts have two much corrosion, oil, grease or soda pop which cannot be resolved with a so called magic spray can. Your in luck as you have function one way or the other for both channels. It will work once you disassemble the mode switch and Potentiometers clean the tiny contacts should be good to go. The buzz effect is a separate problem it could be the Audio cable from the tape head or a grounding issue which could involve a capacitor between the Tape Mech and the PCB.

 

[Myklejay]

Great explanation of your problems, too many times I hear how good Deoxit is. This is an example were the contacts have two much corrosion, oil, grease or soda pop which cannot be resolved with a so called magic spray can. Your in luck as you have function one way or the other for both channels. It will work once you disassemble the mode switch and Potentiometers clean the tiny contacts should be good to go. The buzz effect is a separate problem it could be the Audio cable from the tape head or a grounding issue which could involve a capacitor between the Tape Mech and the PCB.

Thank you Hopey, your diagnosis is what I was thinking as well. A good sign, but still a bugger as these switches and pots are a pain to get to and likely a pain to service…

That said, based on my description of symptoms in my previous post, if you were to choose one of the pots/switches to start with, which one would it be? I’m thinking either the 3 way “mode selector” switch, or the 3 way “radio band” switch.

I’m actually leaning toward the “Radio band” switch, because of the odd symptom that I’m getting with it specifically… which is, distorted (not scratchy like a dirty connection, but actual distortion like sound that resolves once the box is switched back to MONO) this only happens when said switch is rocked several times quickly each way.

Would you concur that this switch is likely the culprit? Thanks again!

 

[hopey]

It's probably all of them start with AM/FM then Stereo Mono. Post a picture some are easy some are hard.

 

[Radio raheem]

I agree with hopey servisol kinda sucks, it is only short term and i have used it for years, I'm not sure taking switches apart is the answer though as most will disintegrate into bit's as there so fragile these days