Sony TC-K777 Restoration Part 3: Adventures with Direct Drive Motors & Transistor Troubles

The restoration adventures with the Sony TC-K777 continue in part 3! This time, I focused on getting the direct drive motors to work up to their specifications. First, I reduced the thrust on the main motor to achieve the correct output voltage on the driving transistors, which significantly reduced the heat dissipation from the heat sink. But the real challenge came when I shifted my attention to the reel motor, which is also direct drive.

🔧 Key Restoration Steps:

Main Motor Adjustment: I reduced the thrust of the main motor to bring the output voltage on the transistors to spec, significantly lowering heat dissipation and ensuring smooth operation.
Reel Motor Issues: The reel motor was stopping during playback as the transistors heated up. After replacing the Hall sensors with little improvement, I discovered the amplitudes from the Hall sensors were uneven, likely due to aging.
Creative Fix: By installing a pot in place of a fixed resistor, I was able to adjust the amplification factor, making the voltages on the driving coils even. The result? The motor ran quietly as it should, and the noise was gone.
Setback with Transistors: Unfortunately, after half an hour of testing, one of the driving transistors gave out. Upon inspection, I found that 7 out of the 8 transistors had already been replaced by a previous repair attempt. However, these were 60V transistors, and I only had 30V replacements on hand, so I’ve ordered the correct ones, which will postpone the restoration for another week.
🎶 What’s Next:

Replacement Transistors Incoming: I’ll continue the restoration once the 60V transistors arrive, getting this Sony TC-K777 back to its former glory.
Stay Tuned: The journey continues as I work through the remaining issues with the direct drive motors and bring this rare deck back to life.
👂 Share Your Thoughts:

Join the Conversation: Have you encountered similar challenges with direct drive motors or aging components in vintage decks? Share your experiences and advice in the comments below!
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🔍 Tags: #SonyTCK777 #CassetteDeckRestoration #DirectDriveMotor #VintageAudio #TransistorReplacement #RestorationChallenges