Got this portable cassette deck. Lights turn on and static on the headphones, wheels do not spin. Opened up the device to check the belt but motor does not turn at all. Took out the motor and tested it with an AA-battery - does work. So where do i go from here?
There are a couple of things I would check before drawing any conclusions. 1. Has the unit been powered with reverse polarity or higher voltage ? 2. Check the continuity of the FG coil (purple wires).
It has been powered through DC input at a higher voltage than 3V I am sure. The purple wires appear to be connected.
Unfortunately there is no datasheet available for the CX183 servo IC. However, given that is was used only in this unit and the WM-3 (as far as I can tell), it's maximum supply voltage can't be significanly higher than 3V. Maybe it's 4.5V, maybe it's 6V; but do keep in mind that unregulated power supplies give a higher voltage than the rating when no load, so you will have an initial spike. So even if powered with a 4.5V supply, it likely received an initial spike over 6V. Given this and the fact that most custom servo ICs made by SONY are susceptible to reverse polarity and higher voltage than the spec, I'd say the servo IC is certainly one of the possibilties. Start by checking the voltages marked on the schematic, especially the one on pin 7 which drives Q603. You need a multimeter to continue this repair, otherwise it's just guessing. Regarding the purple wires, you didn't understand me correctly: what I meant was to check if the coil itself is open (measure the resistance with a multimeter).
Ok I have measured the points and most of them are way off. Here's what I got: Q601=2.0V, 0.32V Q602=0.340V, 0.492V Q603=2.663V IC601: 1=0.104V 2=0.120V 3=0V 4=0.964V 5=0.966V 6=0.269V 7=0.863V 8=1.741V Resistance of the motor is 100 ohms
pin8 should be battery voltage. Collector of Q601 should be lower than battery voltage, because there is a resistor in between. From what you say it's the opposite. Check the resistance between B+ and pin 8 of the IC (with batteries taken out of the unit). It should be very low. I assume that by "resistance of the motor" you mean resistance of the FG coil, in which case it's certainly good.
