Hello,
I bought this Sony TC-850 from CL in non-working condition. My aim was and still is to restore it and on the way learn how to find the parts that are faulty and get acquainted with following schematics. I think this is a rare machine which supports both 2 and 4 track playback and all three commercial speeds, being 15ips, 7 1/2 and 3 3/4, and worth the effort.
When I first got it, even the capstan motor was not turning. There was the characteristic motion of the VU meters then turned on, they moved a little away from the rest position and came back to rest, which gave me some hope.
I checked the servo controller board, noticed somebody has already gone over all the solder joints, thinking that it might have been a broken connection, however, it turned out to be the corroded relay contacts. I have replaced all the relays on both the servo board as well as the system control board. The capstan motor came back to life.
None of the buttons was working until I noticed that one of the transistors on the DC rail was shorted. After replacing it, I continued with replacing all the electrolytic capacitors on the system control board.
Now, I can play, FF, RW but when it comes to stopping, the transport stops as long as I keep my finger pressed over the stop button. The moment I release the button, the deck starts playing again.
No, it is not repairing itself when I am not looking, and no, the counter is not stuck at 9999 and I haven't named it Christine.
I uploaded a video on youtube:
YouTube
The thing I forgot to mention is, if I press the stop button for more than 30 seconds, then the transport stops and it does not jump back to play.
Any idea why this can be time-dependent?
Best Wishes,
Dirk
I bought this Sony TC-850 from CL in non-working condition. My aim was and still is to restore it and on the way learn how to find the parts that are faulty and get acquainted with following schematics. I think this is a rare machine which supports both 2 and 4 track playback and all three commercial speeds, being 15ips, 7 1/2 and 3 3/4, and worth the effort.
When I first got it, even the capstan motor was not turning. There was the characteristic motion of the VU meters then turned on, they moved a little away from the rest position and came back to rest, which gave me some hope.
I checked the servo controller board, noticed somebody has already gone over all the solder joints, thinking that it might have been a broken connection, however, it turned out to be the corroded relay contacts. I have replaced all the relays on both the servo board as well as the system control board. The capstan motor came back to life.
None of the buttons was working until I noticed that one of the transistors on the DC rail was shorted. After replacing it, I continued with replacing all the electrolytic capacitors on the system control board.
Now, I can play, FF, RW but when it comes to stopping, the transport stops as long as I keep my finger pressed over the stop button. The moment I release the button, the deck starts playing again.
No, it is not repairing itself when I am not looking, and no, the counter is not stuck at 9999 and I haven't named it Christine.
I uploaded a video on youtube:
YouTube
The thing I forgot to mention is, if I press the stop button for more than 30 seconds, then the transport stops and it does not jump back to play.
Any idea why this can be time-dependent?
Best Wishes,
Dirk
Do you have manual?
Sony TC-850 - Manual - Stereo Tape Deck - HiFi Engine
The logic is all there. It is reasonably twisted (for 1971) also not drawn for easiest trouble tracing. I do not recall the machine fondly, so am not inclined to stare at it more than that. Good luck!
Sony TC-850 - Manual - Stereo Tape Deck - HiFi Engine
The logic is all there. It is reasonably twisted (for 1971) also not drawn for easiest trouble tracing. I do not recall the machine fondly, so am not inclined to stare at it more than that. Good luck!
Did you check the normally closed contacts of the stop switch,
and the logic steering diodes D618, D619?
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I know it is all there and I have the manual. I am following the connections to the Play relay and it does not reveal anything. In fact, I am not sure what I am looking for. What would be the mechanism that would cause this to jump back to Play mode after being stopped? Is this a capacitor not discharging properly? Is this a diode which is just at the limit of being leaky and certain conditions make it do what it is doing. I mean after all there 77 components to be suspicious about. It wouldn't take too much to replace them all.
Yes, the D618 and D619 checked out within specifications but it didn't occur to me to check the contacts of the stop switch, that is a good idea. I will check that right away.
On a machine of that age I HIGHLY recommend thoroughly cleaning and re-lubricating the motors, capstans (2 right?) pinch roller bushings and anything that moves. I had its cousin the TC-650 back in the '70s and it used the button indicator lights as part of the control logic. Make sure all the bulbs are good and be cautious about using LED bulbs until you're sure they won't change the logic.
I'm very partial to synthetic lubricants from Nye. It is NOT cheap but it is the best.
LOTS of pictures as you disassemble. It's not very difficult to disassemble but may prove tedious. Make sure your screwdrivers are in good shape so you don't bung up the screw heads. I'm also very partial to Wiha screwdrivers which are not particularly expensive - about $9 for a #2 Phillips.
G²
Mystery solved
After receiving directions to look at the silicone components in the logic circuit, I have gone through them again. One of the transistors, the Q607 over the common voltage rail for the relay coils showed slight leakage in the circuit. Suspicious of everything and powered by ignorance, I have decided to replace it. However, when I removed it from the board, it showed no leakage. There was a tantalum capacitor between the Emitter and Collector, so I wanted to check the value of it from the schematic as the writing over it was rubbed off. I couldn't find it in the schematic. After removing the capacitor and soldering back the Q607, the problem was solved.
I am thinking that it must be a desperate attempt by the previous person who tried to address the relay contact oxidation oriented issues, without knowing that they were relay issues and started adding components here and there. Now that all the transport related issues are solved, I am going to take it apart for a good cleaning and recapping the remaining boards.
Thanks everybody who contributed in one way or another.
Dirk
After receiving directions to look at the silicone components in the logic circuit, I have gone through them again. One of the transistors, the Q607 over the common voltage rail for the relay coils showed slight leakage in the circuit. Suspicious of everything and powered by ignorance, I have decided to replace it. However, when I removed it from the board, it showed no leakage. There was a tantalum capacitor between the Emitter and Collector, so I wanted to check the value of it from the schematic as the writing over it was rubbed off. I couldn't find it in the schematic. After removing the capacitor and soldering back the Q607, the problem was solved.
I am thinking that it must be a desperate attempt by the previous person who tried to address the relay contact oxidation oriented issues, without knowing that they were relay issues and started adding components here and there. Now that all the transport related issues are solved, I am going to take it apart for a good cleaning and recapping the remaining boards.
Thanks everybody who contributed in one way or another.
Dirk
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