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« on: April 07, 2013, 08:08:58 PM »
Going out on a limb here, but without a schematic and more advanced troubleshooting aids, if you have some way of implementing a circuit tracer (test probe with something like a .1 mfd. capacitor in series to block DC, and ground wire hooked to the input of another known good amplifier/speaker) and some knowledge of typical board layout and circuit construction, you can put the machine in record pause so it will pass signal, feed a program signal into the line in jacks and "listen through" from input to line output, stage by stage following the signal path, comparing the left and right channels, and determining at what stage you loose the signal to a bad transistor, cap, cold solder connection, or what have you.
It could even still be one connection / pole of the record / play switch or an internal connector, though there are probably not many of those in that model. You can do the same in play, starting at the head output, but you need a tracer with enough gain to be able to hear something till it goes through the first couple of head preamp stages.
Did you say if you got signal indication on both meters or it passed signal in record, source monitor (being 3 head) input to output on both channels?
All of the above should get it down to at least one small area, unless there are multiple circuit problems.
Admittedly, this is harder in some machines than others, due to layout and accessibility to the pcb. And, as the machine is under power, please take all precautions to not shock yourself or short something and make the problem worse.
BTW, used ones have sold on eBay recently for anywhere between $15-$125 + shipping.
Sony and many others including Roberts / Akai made many, many other equivalent 2 and 3 head decks. They may have the same sorts of problems, or others, but probably all will have or develop some sort of issues. I guess it is just a matter of how much time, money and effort you want to put in to restore one of these machines.
BTW, I have a Panasonic and a Lafayette, both small 2 head self contained stereo recorders that exhibit almost exactly the same problem as yours - mostly noise and a bit of signal on one channel in record and play. I was able to get it down to 1 transistor and/or an associated capacitor on the Lafayette, using the above technique and comparing the 2 channels. Just have to get a couple of parts now and throw in there to see if that cures it.
Last BTW, this should be moved to the regular reel to reel machines area as the Sony TC-355 is most definitely NOT a Tape Project machine ! :-)