Need help troubleshooting JVC KD-VR320 cassette tape deck

Need help troubleshooting a used JVC KD-VR320 cassette tape deck that I recently purchased at an estate sale. Not sure how old it is, but I think mid 80s. When initially tested it seemed ok, but started failing soon after I stared using it on a regular basis. The right channel snaps and crackles and has very low volume, although it intermittently sounds normal. The fault is completely random, not physical or thermal, sometimes works ok on power up and fails later or the reverse. Never works normal more than a few minutes.

On inspection I found no visual signs of board or component failures, all solder joints look ok, and no change when flexing or stressing connections or the board and there are no switches or manual controls in the play back circuit. I verified the source tape on another player and the amp and speakers with other audio sources.

Probing and prodding around the circuit board near the termination of the wires coming from the heads I noticed that I could stimulate normal sound briefly after touching any of several component pads with my finger. Note that touching or pushing the same pads with a wooden probe had no effect so I don’t think the issue is physical. Using a metal probe I was able to isolate the effect to specific pads connecting to the C1228HA pre-amp. Touching the top of the only electrolytic cap included in the fore mentioned components also effected the sound, so I replaced the cap, but no improvement. Also, re-soldered all the fore mentioned circuit board pads.

What does touching the pads tell me about the problem? I assume it adds some capacitance to the circuit and allows the pre-amp to return to normal operation, but does that mean I have a bad capacitor or is the amp bad? Also, I haven't been able to find a service manual or schematic for the deck if anyone has one.

 

There are no pots or mechanical switches in the cassette play back circuit. Gain is controlled on the separate JVC amp unit which has been confirmed good. The only pot is in the record circuit. But good to know that WD40 can be used on pots.

 

That is the system in the picture. The slider and pot next to it is the volume and balance control for the record circuit.