Chasing the Sony CX20084 speed chip for D6C walkman

Here is corrected gerber files, as I promised. And some little more detailed W&F measurements with quartz lock on, and pictures of replacement board from infrared camera after playing a tape about half on an hour. BOM and assembly drawing is not ready yet, will post them later with installation instruction witch I'm currently working on.

 

Thank you! Actually, I have two units - D6 and D6C, and W&F is the same on both of them, mayby slightly better on D6 because of it's small usage. D6C has significantly signs of wear - I think, it's really been used by journalist, because pause button surface is polished.

 

Great work, thanks for sharing

 

Anyone looking for an original chip?

 

That's funny, that sealed IC has only sentimental value if one wants to collect it. Is there anyone collecting NOS parts (without the intetion of ever using it) ? I wonder...
For everyone else, donors can be bought much cheaper (remember donor doesn't have to be a D6C), then it's the new Chinese board alternative and the BA6301 solution presented by @LeKos.
With 3 significantly cheaper options available, I honestly fail to see any value at all in this listing apart from potentially being a collector's item.
Even a couple of years ago when I could still get these genuine NOS CX20084 ICs, they used to cost less than 1/10 with shipping included.

 

Making an instruction actually took more time than I suspect. Now I think it`s ready, but maybe I missed something, so if you have any questions, I will try to help. So…

Desolder:
Components within blue line.
Wires from motor (red and white).
Wires from FG coil.
Brown wire #15.
Blue wire #17.

Also remove R603, R604.
R604 need to be replaced by 300k resistor, R603 need to e replaced by 330k resistor.

Existing wires soldering:
Red wire from motor solder to the same place as brown wire #18.
Wires from FG coil connect to "FG+" and "FG-" pads on replacement board.
Blue wire #17 and brown wire #15 connect to "Blue" and "Brown" pads on replacement board.
White wire from motor connect to "M-" pad on replacement board.

And there are some new wires needed:
Wire from "GND" pin on replacement board solder to the same place as black wires #4, 25, 43, 44.
Wire from "+10V8" pin on replacement board connect to the same place as orange wires #14, 11.
Wire from "+5V" pin on replacement board connect to pad for pin 5 of IC601.
Wire from "To pin 4 of CX20084" connect to pad for pin 4 of IC601.

And you need to add a 270p cap between pins 5 and 8 of IC701 on Auto OFF board for proper working of quartz lock mode.

After installation adjust RV603 with speed tune set to on and RV602 on center position.

Adjust RV601 according to minimum W&F with speed tune set to off. This is the same adjustment as described in "Tape speed adjustment" in service manual, but I`m not sure about proper speed. In my unit, with "Tape speed" solder joint removed, I have speed about 3240 Hz on 3000 Hz test tape. Be careful - instead of original, in my current schematic this adjustment have smaller area, in witch PLL lock works properly and stable. If you can't obtain stable small W&F, try to increase R715 on Auto OFF board, decreasing additional capacitor's value from 270p. I have the same stable results with R715 changed to 3.3 MOhm and 120p capacitor. Also you can try to increse a value of R603 and decrease RV601 - theoretically it should simplify the adjustment.
All of this is more tricky than original procedure, and I can`t guaranty that it will work. In my case it works perfectly, but if in you case it don't, just replace R603 by 300k, remove "Tape speed" solder joint and adjust speed by RV601 to obtain correct tape speed. Quartz lock will be disabled, but unit should work stable.

In attachment there are pictures with instructions, BOM and gerber-files. Gerber files are the same as before, attached them here so that everything - instructions and gerbers - was in one place.