Hi everyone, I have a Sony WM-7 that is currently dead and showing no signs of life. I’ve been trying to diagnose the issue using the service manual, but I’m running into some challenges and would greatly appreciate your input. Here’s what I’ve observed so far: When connected to 3v DC jack (verified voltage and polarity), the motor spins briefly (about a second) and then stops. Pressing the FWD button causes the FWD light to flash once, but nothing else happens. The battery terminals are corroded, but I’ve checked and confirmed that there’s no corrosion on the circuit board itself. All capacitors appear visually fine, with no signs of leakage or bulging. I’ve measured voltages at various points in the circuit as per the service manual, but some readings are not as expected. Also just connecting the ground on the DC jack connection shows 1.35v on my mutimeter. Dont know whats going on there. I’m not a professional, but I do have some basic knowledge of electronics. Could this be a power supply issue? Any pointers on what I should check next would be really helpful. Thanks in advance !
UPDATE: Used come contact cleaner on all switches and buttons. Checked continuity on all switches including hold/release switch and door latch switch. Also checked voltages on the control circuit flex ribbon. Getting 3v on all pins irrespective of pressing the buttons or switches.
UPDATE: Fixed the battery terminals and added a new battery spring. The old spring was corroded and missing. Also noticed that pressing any button (fwd,ff,rev,rewind), the capstan motor tries to spin after a few seconds. Can't hear the actuator motors turning at all. The few seconds delay between the button press and the capstan motor trying to spin, could be that the actuator motors are trying to engage the mechanism but fail. I'm thinking there might be two issues: 1. Either the caps are bad and cannot provide enough power to the actuator motors to engage the mechanism. 2. The old grease on the mechanism has gummed up and the actuators cant move it. Could be either one or both.
The DC-DC convertor on this unit only powers the Dolby circuits, everything else being powered by the main 3V rail. So even if that was to be faulty, it won't affect normal operation. About capacitors, the main power rail goes directly to pin 25 of CP801. Only caps that may affect the logic controls are C305, C306, although CP801 should work without them. Old grease is indeed a potential culprit, but also the 2 mode swtiches may need cleaning. If the microcontroller doesn't know the position of the mechanism it will act erratic. Hold switch may also be a problem, since it's in series with the buttons. S306 also needs to be closed for logic controls to work. Fact you mention at point 1 of first post shouldn't happen. Just inserting the batteries/connecting DC jack shouldn't trigger any movement of any motor or light up any LED. Don't really understand what you're saying at point 6.
Okay, so to get to the 2 mode switches S806 S807, I would have to disassemble the mechanism. I've been avoiding touching the controller flex cable. Is there any way to do this without desoldering the flex cable? Ive read its very fragile and easy to break. Any tips on how i could make the desoldering process easier? Ive cleaned and tested the hold switch and the door latch switch S306. They both test ok for continuity. Also point 1 doesn't happen anymore. It just happened the first few times i powered it on. Point 6 after some googling, found out that i was experiencing some capacitive coupling, which i did not know about. So that was just me being inexperienced.
The flex cable doesn't need to be desoldered, entire board tilts after desoldering the 4 motor wires + battery wires + white wire coming from buttons PCB. After board is tilted, the plate with reels can be removed/tilted. Note there's a spring that needs to be removed first.
hello @Valentin ive cleaned and lubed the mechanism and now the mechanism is working well. Turns out it was old grease and switches S806 S807 that needed come cleaning. Unfortunately, someone else previously had tried servicing the unit. After a lot of hours spent going through the service manual, i found out that that both extension springs (part no. 333) for the fwd and rev mechanisms were missing. Do you have the dimensions for these springs? Maybe i can find them somewhere online or check some local places where i can find them. Also, without any cassette in the unit, there are some crackling sounds when pressing any button. And also lot of static noise (like plain white noise) on the left channel which increses and decreases with volume adjustment.
Springs you will find on Aliexpress, but you need the dimensions (length, diameter, wire diameter). Will try to update later on regarding the dimensions, don't have them at the moment. Fact you have noise on L channel that goes up and down with volume suggests the amplifier is on, despite it shouldn't be unless unit is in PLAY mode. More investigation is needed, but you have significant progress already.
I too am suprised by the progress, i thought this unit might have some power delivery issues. Dimensions for the springs will be greatly appreciated. I'll try to post a video with audio, it might help in troubleshooting. Thankyou for all the help
Springs (part no. 333) have the following dimensions: OD (outer diameter) - 1.5mm WD (wire diameter) - 0.1mm L (total) - 5.5mm Closest I could find at a first search is a 0.2mm x 1.5mm x 5mm: https://www.ebay.com/itm/266869659003 Haven't managed to find any extension spring with 0.1mm wire diameter. One option (if you can't find a match) is to use a spring that's longer compensate for the higher wire diameter.
This is a local seller here in india, https://www.leespring.in/extension-springs The smallest spring with wire dia 0.18mm (Part Number: EI 007A 01 S), should work i think. It has a longer length which should compensate for the larger wire diameter. Or i could get a spring kit from them https://www.leespring.in/spring-kits and see which size works.
