Hi, I had bought a DD100 advertised as completely dead. I checked the servo IC CX80084 and I figured out the pin 7, supposed to have 3V coming out of the auto-off circuit, had nothing on it and shorted pin 7 with pin 8, which did have 3V on it as it's connected directly to the batteries. The walkman started working after doing that, but it has had one very annoying issue since - during rewind AND fast forward it will turn off much too early, way before the end of the tape. The tape length doesn't matter, it always stops around the same point and refuses to continue rewinding if you engage it again - it will just stop again after a moment. The FG coil is not defective and I tried swapping it from another, working DD, to no avail. I have also replaced all transistors and capacitors in the auto-off circuit and even the CX20084, just in case. Yet, none of this has yielded any results. The Khan still engages the auto shut off before the end of the tape in rewind and fast forward modes. It also happens in fast forward. I'd be grateful for any ideas as to what could be wrong - I've run out of mine.
UPDATE: It now randomly happens during play too. It will play normally for some time and then shut off. None of this is mechanical, I'm talking purely about the electronic shut-off that cuts off the power to the entire unit.
This is copied from the Sony WM-DD repair guide have you done this?: The walkman must be in PLAY operation. Connect the walkman to the power source, without a cassette inserted, and hit the PLAY button. There are two methods to achieve this: a. Measuring the power consumption of the walkman using a multimeter. Normal consumption is 80 – 130 mA, depending on the model of walkman being used. As you tighten the adjustment screw, consumption will rise. As you loosen it, consumption will be lower. If you release it too much, you will get to a point, where the motor loses its contact with the rubber ring and consumption will not drop any further. Instead autostop will be activated and you’ll have to hit the PLAY button again. Tighten the screw until consumption starts to rise. Example: You measure a 70 mA consumption when the plastic adjustment screw is unscrewed too much, i.e. it motor has no contact with the ring. Now, tighten the adjustment screw until the consumption starts to rise. When you measure 90mA, the adjustment is done. Check it by trying to stop the capstan ring with your finger. If you can feel a torque, then adjustment is OK. If you feel that the rotor slips on the rubber ring, tighten it little more until you feel a torque. b. Using finger-check method. Find the point, where the rotor stops slipping on the rubber capstan ring. Do not tighten it too much, just ensure that it doesn’t slip. Apply screw lockers to this adjustment screw.
Also sometimes the metal part from the center gear is pushing to hard on the gear so there is to much friction on the motor and it shuts off.
Thank you, I have checked your reply only now, after figuring out it was about the drawn amperage. I forgot the DDs work out when to stop based on that factor too. I had a new rubber ring from mikohm and I noticed it didn't have the slight slope the original had. It was causing the motor to draw too much power from the circuit, resulting in the unit shutting off. I returned to the original ring and adjusted the friction, the problem now doesn't occur on playback and fast forward, but it still happens near the end of the tape on rewind. So, unfortunately, I do not recommend buying that rubber ring from mikohm, it can break your walkman! Better get one that has the proper slope, the rings from Ukraine have it.
I shall make some mechanical adjustments, despite adjusting the friction and with the old ring, I get 123mA of drawn current at the end of tape rewinding, definitely why it shuts off automatically.
Well, it turns out one of the reels was gummed up a bit, I lubricated it and now the unit operates properly, but only on the old ring.
