In the last post I explained how changing the belts in the TEAC A360S cassette deck were successful, but that the tapes did not actually play. New belts and proper lubrication allow the mechanics to operate, you know, move the tape and such, but everything else was out to lunch. The meters did not work, the sliders appear to be inoperative, and the various switches did nothing.
That generally means there are some problem in the electronics, and that can be a real mess unless one is willing to get heavily involved with tricky diagnosis and difficult repair. In the photo on the right we see that the primary circuit board is a mass of wires, capacitors, diodes, resistors, and transistors. This machine is so old that there are no integrated circuit chips. Everything is hand-soldered.
The good news is that the TEAC A360S service manual is readily available online as a downloadable PDF. In fact, original manuals can be purchased on eBay. The image on the right is from the PDF of the manual. The service manual has a trouble shooting list and that offers some insights and possible solutions.
According to the service manual, if the audio in playback mode is intermittent or absent the problem could be with Q-101 or Q102. Now that is interesting! But, what are Q-101 and Q102? The “Q items” are, as it turns out, transistors.
The manual also says that if the VU meters are inoperative in play mode the problem could be with the meters or Q-104. Other issues could be problems with Q-103. Hmmm … now this is getting to be interesting.
By cross-referencing the problems and the possible solutions, I figured that the most likely issues could be with Q-103 and Q-104. By examining the diagram shown above I was able to locate the approximate position of these transistor on the primary board. The trouble shooting guide also says that the components noted in the guide are for one stereo channel only and that identical components are required for the other channel. So that means that Q-103 has a twin called Q-203.
I figured that as long as I was at it I should change the two main capacitors as they are likely to fail and they are not expensive. My shopping list now consisted of Q-103, Q-203,Q-104, Q-204, and 2 1000uF 35v capacitors.
Unfortunately, all those parts are obsolete and discontued.
Happily, all those parts have modern equivalents and I was able to find new substitutions. The only difference was the capacitors as I had to purchase a pair of 1000uF 50v units. The voltage difference is not a problem, so it looked like I was ready to go. I ordered part from DigiKey and all was golden, so to speak.
The next step is to swap out the bad parts for the good parts.