Iirc a ak member Brian said that these tuners were problematic even when new and working on them was a even a pain in the ass when they came out. Ff 50 years and the problems can be even worse.
After this many years most all the electrolytics are gone bad. The symptom you describe sounds very much like a capacitor that opens up after on a while, especially since the voltages appear to be correct. Capacitors are famous for such problems. The sockets of the transistors may have been gold plated, but the leads of the transistors usually were not. Dissimilar metals in close contact are not a good idea and can cause electrolysis to take place especially when combined with humidity and air pollution. Sometimes removal and reinsertion of transistors may restore enough corrosion free contact that a circuit will operate again for some period of time.I've been working on the TFM-1000 and replaced about 5 electrolytics that were visual leaking. Cleaned the controls once again. Now the tuner sounds much better but the output volume is a little low. Also, the biggest problem is that after about 10 minutes of playing, one of the channels slowly fades out. Voltage checks are within tolerance even after the one channel stops working. I sure there is some part(s) that when heated up fails - which is causing the one channel to stop working.
I feel transistors are either good or bad so it's probably a cap or a resistor. But as previously suggested I will clean the transistor leads and sockets just in case.
Any additional suggestions would be gratefully received.
Thank you.
Spray some DeOxit into a cap. Then dip the transistor legs into the DeOxit. Insert the transistor into the socket and pull it out again. Then repeat this a few times. Finally give the socket a short blast to flush out what contaminents remain. The transistor legs should have cleaned up from the friction also. If not wipe them on a clean kitchen green nylon scrubbie with some DeOxit sprayed onto it. Then re-insert them into the sockets.
I looked for those transistor x-ref on my 2 desktops. Not there. Probably on my old dell laptop that has some serious power problems. I'll see if I can get it running long enough to dump all the manuals to a flash card and transfer them.
Do you have any canned air??? If so turn the can upside down and when the problem starts, give each of the transistors a very quick shot of the spray. It'll cool down the transistor and hopefully it'll come back up enough to show it's a heating failure for that part. Don't use a lot, and frost the part. just enough to cool it down.