Hello all. I recently found a WM-D6C in a flea market. Although it is very old (serial is 8XXXX) the walkman is in very good mechanical condition (except for the belt is slightly looser.)

Sorry to rant, in a nutshell:
The WM-D6C motor is NOT meant to run continuosly is it? (I think not... read for more details please)

I am not very experienced with this machine, but I did manage to find the manual that came with it. So my story begins like this:

The first thing I noticed about the machine was that when I placed in the batteries, the motor immediately began spinning. I had not engaged any controls at all yet. Still, I placed in a UX-90 tape, connected my earphones and engaged play and yet the machine played the tape at a very stable speed (no faster or slower by ear, though I have yet to try it with a proper test tape and CRO). The machine responds to tape speed control well too.

It also produced a very warm sound (and loud! almost sent me flying with slider on 4.) Granted the LH channel is weaker but I can adjust the gains, biases and azimuth myself later. Also the pause control engaging before record is meant to engage heads onto tape anyway? At the moment the mechanism requires you to unpause-pause to get it to REC PAUSE. But this is not what I'm concerned of (minor problem.)

As I tested more features this thing, the motor problem has become more of concern to me. Firstly, I noticed the motor is running way too fast (its running off full 6V!!! The servocontroller should never drive it this fast and in FF and REW it runs off the same circuit!) The motor does slow down when you engage REC/PLAY/FF/REW immediately though. OK, I know some tape decks keep their motors running constantly but on a portable??

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Ok. With the help of a friend, I have acquired the service manual. Upon studying the diagram, I noticed the motor is driven (along with the servocontroller, IC601 (CX20084) off a seperate always connected 6V rail. This is a nice design - a electrically switched motor. Unfortunately I have heard that the CX20084 is particularly fragile part of the system (and no doubt too: its DIRECTLY connected to the 6V WITHOUT any sort of protection.) Even worse, this CUSTOM part seems discontinued by Sony! I have yet to find a datasheet on this IC so for now, I can only hypothesize its operation.

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Ok. I have just tested the transistor that drives the motor (Q601). It seems fine, but then again, all component tolerances can be accounted for on motor drive side with servo feedback.

I believe the main power supply for IC601 is PIN 8 (Correct me.) Also, PIN 7 is normally pulled high by normal rail for the IC to work - it is pulled low by switching circuits for auto-off during REW/FF. Perhaps only part of this chip is dead and so it just doesn't switch off properly, but as this looks like a CMOS logic chip, this is extremely oddball.

If this is the case, I can substitute the power supply to IC601 with transistor switching by the switched 6V rail (like it was originally intended.) What bugs me is I have to somehow fit that in the walkman (this old version doesn't use that many SMD parts.) I hope the IC would last out as it seems very hard to get now.

Please share your opinion, as I am no expert in this area.

Common problem I'm afraid, caused by someone connecting a power supply & reversing the polarity by applying the plug to the wall socket upsidown. The motor servo control circuit has blown. Sadly this part is soldered to the main board & is a fiddly fix.

Thanks for your reply, agentorange .

Yes, unfortunately this is a SMD package IC . Its been difficult for me to find a replacement for this since its been discontinued by Sony.

But as I said, only part of the IC seems faulty (or so from how I think it works.)

Please, can someone that knows more about this part (or has a datasheet) share their expertise with us? I take that my hypothesis on its operation is correct?

EDIT:

Hello again. Those with later board revisions are much less likely to have a servo problem: the servo circuit in the newer revision (looking at Supplemant-2) uses mostly SMD components. The servocontroller is now a smaller 8 pin IC and is protected (and switched) by several other transistors and a MOSFET.

But at least this proves the theory of CX-20084 operation: it was designed to switch as well, with mostly everything integrated into it. The circuitry otherwise is very similar.

Anyone know anywhere to get a new belt? The CUE/REVIEW function was slightly faulty (did not disengage slipping clutch properly) and so the belt wore out (it stretched) and the playback auto-stop doesn't work now.