WM D6C repair notes

[chriswood1900]

WM D6C
Working through my round to it pile I decided to tackle three Sony WM D6C cassette recorders that I variously acquired some time ago, one was working although would not record properly with no control over the input level the other two were dead I believe as a result of wrong adaptors being used. All three were early ones with the amorphous heads and mainly through hole parts.
The two dead ones both had the CX20084 surface mount chip burnt out and no control over the motor speed so I ordered a couple of them, on fitting them one started to work on playback but could not FF or Rewind so I started to check though the mechanism to discover the idler wheel did not move across when it should and there was no FF or RW drive. To understand how it worked I looked at the other one I had open and found the idler is spring loaded and applies gentle pressure onto the edge of the flywheel, on the one I was repairing it was seized solid. I tried gentle application of some penetrating fluid and with some pliers managed to eventually get it to move a little but not freely.
Setting that one aside I thought I would do number 2 however on powering it up the speed was erratic and the 11V line missing as a result of failure of the DC-to-DC converter module. As things weren’t getting any better, I was contemplating doing some swaps and building one good one out of 2 I opened up the module not an easy task as it is very small and soldered shut obviously not intended to be repaired, it is a small joule thief that takes 6v in and puts 11v out. Inside there had been a complete conflagration with many parts just burnt up and tracks damaged. This looked like the two into one was the only way, and I considered putting the working mechanism with the working electronics but a quick look at the dozens of wires that would need transplanting that didn’t look good.

Back to having another go at the stuck idler, 1 removed the idler wheel and the plate on previous machine which came out easily on the other machine there was some slight movement but on removing the circlip it seemed stuck solid. I removed all the parts around the idler including the flywheel, the motor, and then applied sustained pressure to lever up the plate and spindle I was concerned I would damage the delicate thin metalwork but is eventually gave in with just a bend removable idler plate. I do not understand why it was stuck as I have never seen grease go that hard, it was as though it had been glued in place. Once I had access to the post, I could clean off the congealed gunk on the spindle with IPA and with a little bit of lithium grease fitted the idler plate from machine 2 and reassembled the mechanism, it all worked as it should although the speed was wrong and the high frequencies poor. That was a simple case of going through the speed setup in the service manual and then setting the azimuth, this was a bit harder as the screw had been screwed down so tight it had compressed the spring to the point it would not return to the correct position but a bit more dismantling re-tension the spring and it set up nicely.

At last, I had a machine that worked properly. On to the next one with the recording fault, when recording the rotary record level control acted as an on-off switch either full volume or nothing so it was carefully de-soldered and when measured it was open circuit not the 50K it should have been, maybe the control had received a bash cracking the thin tracks in the control, looking online I could not find a suitable replacement so I removed the one from what has become the donor machine which tested fine and soldered that in. put the machine back together and tested it and all is now working fine.

I did a final check on the two working machines to check azimuth, wow and flutter, Dolby levels and record and playback functions and both performed according to spec.
So in conclusion I have two working well and one that I will keep as spares unless I can source a DC-to-DC converter, a new idler carry plate and a record control potentiometer!
Just as I finished this I was put in contact by a friend of a friend who had suffered exactly the same fault with the stuck idler so it must be a fault that occurs on other machines.

The sources I used for information were:-
Service manual https://elektrotanya.com/sony_wm-d6c.../download.html
DC-DC Converter
http://stereo2go.com/forums/threads/...ter-fixed.421/
https://martin-jones.com/2019/01/01/...verter-repair/
https://www.vintage-radio.net/forum/...d.php?t=166216

[Ted Kendall]

Originally Posted by chriswood1900

I do not understand why it was stuck as I have never seen grease go that hard, it was as though it had been glued in place.

I have - this evil stuff was used on the TEAC dual capstan machines and was quite capable of sticking the pinch roller plate absolutely solid. Superlube for me!

[TIMTAPE]

Temporarily heating up the bearing with say a soldering iron tip can soften the old grease enough that less force is needed in dismantling.

[saxmaniac]

I did repair a dc to dc converter a while ago and did a crude layout with component values. The transistors are not critical and something that will physically fit and handle as much current as possible for robustness will do. The tantalum capacitors are suspect but it's a very simple circuit, just fiddly

[saxmaniac]

Ps
If you can't salvage the converter, I bet you could get a small 3 pin converter, must be stabilized though. Can't remember what current it carries but it's very small, but most load is during record if you're aiming to measure it