Hi, I’ve been trying to repair a Sony Walkman TPS-L2 for a while. It arrived with a stuck motor and worn-out belts. I managed to free the motor using some watch oil and replaced the belts. Now the motor runs, but the Walkman stops after a short while. My hypothesis is that it’s an issue with the speed adjustment on the SERVO AMP BOARD. Here are my observations: During playback, the sound runs fast. The motor stops even when the belt is removed. If I wait a bit, the motor stays on longer (~5s); if I apply power again, it shuts off almost immediately. As shown in the photo, at point A I have 2.7V when powered on, and at B 1.4V. When off, B goes down to 0.5V and continues to drop (capacitor discharging). From these observations, I rule out the mechanical part since it stops even without the belt. I suspect it might be a capacitor issue, which could explain why letting it sit for a while (allowing the capacitor to discharge) lets it run longer — probably by opening the circuit on the transistor, I imagine. I might be on the right track, but I’m not 100% sure about this hypothesis. The capacitors have too low a rating to be reliably tested, so they would need to be replaced directly (something I’d prefer to avoid, especially since many are hard to find or would have to be ordered). Just to be sure, what else could it be? I’m also attaching a video of the problem where I do normal play, rewind, and then play twice in a row:
Ok, I did a check and indeed pin 3 outputs 2.7V instead of 0.4 (pin 2 also has a different value, but it’s correct when the motor is running). I also checked the whole part of the circuit around pin 3 and everything seems fine. At Q601 I’m getting wrong voltages at its terminals, but I think that’s due to the output voltage from pin 3
Have you tested the motor outside of circuit ? Would want to make sure the motor itself doesn't have a problem before suspecting anything in the drive circuit. Fact the shaft is moving up and down during rotation isn't normal. Also you need to check the FG coil actually produces a signal when motor is running.
Exactly, I also noticed that the motor shaft has quite a bit of play. Anyway, I disconnected the motor and, when powering it externally, it runs correctly, and from the coil output I get a sine wave with 0.03 Vpp.
Small update: to narrow things down, I ended up doing what I really didn’t want to do, disassembling the motor mainly to fix the excessive wobble. I think I did a decent job. As I read in another thread, I tightened the shaft until it had about 0.5 mm of play, and rotated the brush section until I got a current between 10 and 20 mA (managed to get it to 15 mA). It seems to run better than before, but the issue is still there. I also tried bypassing the speed adjustment with a fixed resistor instead of the potentiometer, but no luck, same as before. I checked a few components and they all seem fine, so unless there are other possible tests to try, tomorrow I’ll remove the board and go through each component one by one, ruling them out. Do you think there’s a chance the CX184 could be the problem?
Another update: I did something else I didn’t really want to do to test the board. I disassembled another working TPS-L2 and bridged the cables between the broken Walkman and the other board, and apparently the problem remains. So the servo board is not the issue. Now my doubt is what else it could be . Because even if I remove the belt, the motor still stops after a short time, and the main board doesn’t seem to have anything to do with the auto-stop function.
I didn’t want to remove the motor from the working unit, but I realized I can actually test it without the belt since it stops anyway. So I bridged the cables between the two, and the good motor stays on and works fine. So yes… the problem is definitely the motor. Since I’ve already disassembled and reassembled it following the instructions from the thread, what else could it be? The current draw is the same as the working motor. The only difference is that the purple signal wires don’t give the same values as the good one — in fact, they give almost nothing, just like in my first test. But if I disconnect the purple wires from the board on both units, the good motor keeps running, while the bad one stops after a short while, just like before. What could be wrong inside the motor?
What's interesting is the motor works when powered separately. I would test the motor on a power supply and vary the voltage, maybe there's a dead spot on the commutator. See if the motor still runs at 0.7-0.8V. Compare to the good one.
