Hi, I am working on a nice F100III and was hoping to get some much appreciated help from some schematic experts. The unit is serviced/working well mechanically but the solenoid will not activate with the green button (no voltage is released). I believe both the solenoid and photosensor work as it changes directions at the end of the tape. S702 is clean and works. Electrolytics replaced. I've checked a lot of the resistors and tantlums in the area for shorts. With the board off and S701 shorted, I am getting voltage readings as per the photo, in RED. However, I am not getting the waveform .7-1.0V when I touch S702 on the scope. Before going any further, I would be interested and any other thoughts on what would prevent the solenoid from firing. Thanks in advance!
Hi, I thought I would bump this up before it gets buried too deep. If anyone has any thoughts, that would be much appreciated. I will continue to poke around!
Ok, some observations I made on the last transistor that controls the solinoid. The yellow is the base and the blue is the collector. On the ‘bad unit’, the end of tape auto-reverse fires a 120-140ms charge and it works fine. When you hit the green button, the bad unit seems to fire around 13ms on the base resulting in 5ms to the solinoid before the voltage breaks up a fair amount. On a known good unit, the base seems to fire about the same length but the charge to the solinoid is cleaner and twice as long (10ms) before it wobbles. Interesting for sure. Looks like the signal is not be clean enough through that last transistor or the solinoid has degraded to some degree. Anyways, I thought I would share.
Have you tried replacing the acual solenoid ? (assuming you have access to spare one). Seen a similar problem on a WM-109 (which is essentially from same series), with similar behavior of pulse not being wide enough and having that bounce. In my case, the walkman would not engage in PLAY after being left unused for a couple of hours. But after pressing the button many times it would work fine. Swapping the solenoid seemed to have attenuated the issue, although not fully fixed.
Thanks so much for the response Valentin. I may actually have a solenoid I could try - let me check. I assumed it was OK since it worked with a longer pulse but I will experiment. Do you think it is possible to lengthen the pulse a bit with a higher uf cap at c709? Just thinking about what actually controls the length of that pulse.
C709 controls the slope after the voltage has dropped to 0V. Higher capacitance on C709 will render a slower rise back to 1.5V. This is used for debouncing the swtich. You can however try changing C707 to a higher value (10uF, 22uF). It's to be noted the time voltage stays at 0V will also increase by doing this, which can render solenoid being engaged for longer than it should. Would also check that R726 since the voltage you have there differs significantly. You can also try a lower value (47k), so when Q714 is on it will pull Q715 base "harder" to GND.
Thank you Valentin! This is extremely helpful. R726 is reading 100k in circuit but I agree, the voltage drop is not as expected so I may try to replace it first. Other than that, I will play around with the other values and find that spare solenoid. I’ll keep you updated.
I managed to swap some components last night. I tried both 10uf at c707 and 47k at r726 and no real change. I don’t think q715 was switching at all in one of the scenarios. I put c707 back to 3.3uf (new) and tried r726 at 150k to get that voltage down at the base to better drive the 0.7v switching? I also replaced r725 while I was in the area. Success. I am not definitively sure what fixed it (could have been a bad resistor/tantlum although reading ok) but I am pretty happy with the outcome. I never did try a new solenoid. Thanks Valentin for the guidance and this was an interesting troubleshooting adventure.
