The Sony TC-K81 Tape Deck

I had this lovely old tape deck dropped in for repair recently, my customer had recently bought it and had been told it needed belts, this seemed reasonable seeing as it was built around 1980, he even brought the belts for me to fit. But it was soon apparent that he had had a go himself as the deck wasn’t secured inside the case and was hanging loose, at this point I would normally turn it away but the thought of consigning a nice piece of 40 year old Hi-Fi to the skip was too much to bare, so I took it in.

It was a bit of a fiddle to fit the belts and reassemble the deck, especially reattaching the mechanism to the casing, the customer had lost two of the screws that hold it in place and one of the others had a chewed up head, so, some new screws of the right size were found for it. Now to test it out…rewind and fast forward fine, as would be expected because those two modes have a separate motor and do not rely on belt drive, unfortunately when play was pressed all I could hear was the click of a solenoid and nothing else. Feeling a little annoyed I removed the deck again, this was obviously the original problem, not the belts. As the solenoid was firing when the play button was pressed it was obviously a mechanical problem, not an electrical one, so both flywheels were removed to reveal the main cam gear, this is held in an idling state by a pivoting arm with a hook which, when the solenoid fires, releases the cam to flick in an anticlockwise direction allowing it to engage with the small gear on the flywheel, thus lifting the mechanism into the playback position. But as I fired the solenoid manually I could see the hooked arm release the cam but the cam wasn’t going anywhere. Out came the hooked arm and then the cam gear, very hard to remove as the grease had hardened on it’s shaft, effectively glueing it in position. A bit of cleaning and lubricating had the cam gear once again moving freely on it’s shaft, as can be seen in the video below.

The solenoid can bee seen to the right, the cam gear is the right hand of the two large gears and is connected to the solenoid via the hooked and pivoting arm, as I actuate the solenoid with my screwdriver you can see the hooked arm release the cam gear which then flicks in an anticlockwise direction. The flywheel would be sitting above the cam, already rotating in a clockwise direction and would engage with the cam to lift the mechanism into it’s playback position. In the video below I show how this works.

Finally after refitting both flywheels, all the belts and coaxing the deck back into it’s position in the casing, it was ready for a test and thankfully it all fired up perfectly, a couple of hours spent listening to my small collection of cassettes told me all was well. It was a rewarding couple of hours spent in my workshop and thankfully it was another beautiful piece of vintage Hi-Fi I was able to keep going for many more years.