This is a repair of this Sony d6c stereo cassette recorder, this is the new revision with glass epoxy circuit board and SMD components, problem was speed was two fast and control of speed using tune control on the back, was cause by a defective CX20084 IC, which took from a different part unit, now works at correct speed and tune control works, You can find a replacement IC on eBay, this is a common issue with these.

Great Job! I'd like to hear your honest opinions on which board revision of D6C is the best:

The through hole brown phenolic board, 2nd-3rd generation SMD, or the 4th Generation SMD (2001 onwards, thinner board, revised servo circuit).

According to the service manual, there should be 4 revisions.

So which revision is the best ? 1st, 2nd, 3rd or 4th ?

1st is the best, the others, changes were made for cost cutting. But for a reliable one if on buying Ebay go with the 4th with low hours, because less wear on rubber parts, unless you find one restored or brandnew older revision.   

Those reasons are exactly why I just got a very high serial number 4th revision D6C.

(in the past few weeks, I've got this new D6C to "replace" my older, slightly worn out 2nd revision D6C. Also did repair work on both, mainly capacitor replacement.)

Some observations:

Nearly mint condition. Perfect Rubber and head, zero wear. Permalloy head like my older 2nd revision D6C. Sony finally removed the amorphous head badging.

Some Capacitors need to be replaced: some tantalums (the ones plop mentioned in an older thread) on the playback path and recording bias path. Mylar capacitor for the Servo circuit.

Circuit board is much thinner/cheaper than earlier SMD revision. I also noticed the Factory Bias is different than my older 2nd revision D6C, which may be re-calibrated for the later Sony tapes. (It's BETTER!)

Like my older D6C, it also STILL has some motor hum on higher volume settings, despite having several electrolytic capacitors replaced as well. I'd need to eventually figure this out. It's starting to seem to be a trait on D6Cs: I've seen other D6Cs on youtube with this exact problem.

After all the capacitor replacement and an azimuth tune-up, it sounds and records much better! It also seems to be perfectly biased to my current tape stock, Late version UX-Pro.

It sounds and records so much better than my old worn out 2nd revison D6C, It's hard to believe they are the same model!

Now I'm interested in a 1st revision D6C,  especially on the supposed better reliability and sound quality. I'd like to know if the through hole board has less capacitor problems, and of course the presence of that laser amorphous head.

Bub,

Just a thought regarding the motor hum, are you using batteries or an AC mains adapter?

Happens on both.

D6C's are not suppose to hum, as mines are silent, of course except for music and tape hiss, even at 10. You may etheir have a bad transistor in the DC-DC converter check the 11v rail, or leaky transisitor somewhere.

Hey retrodos, have you encountered this issue in your D6Cs before? If you did, which transistors did you replace?

Aside from the DCDC converter, should I be looking for problems on the headphone amp or servo stage transistors?

Check the servo stage first, if speed tune changes the hum's pitch the problem is your CX20084 IC 601, their also another transistor in that area that needs to be checked I had one of the newer revision, the the hum was pretty bad unless you turn on dolby on and assume it was the caps and noise filtering caps and turn out to be that IC, now works with no hum.  

Yes, speed tune changes the hum's pitch. Hum nearly disappears with dolby on.

I am assuming that transistor to look out for is q601.

If this is the diagnosis, all I need to do is to hunt down 2 of these ICs and learn how to replace them. (Note that neither of these D6Cs have servo/motor/auto-off issues otherwise.)

EDIT: Revision 4 uses a different IC (CX609A), and a separate comparator.

I would also check the belt make sure the belt tension is right not loose or to tight and also the tire and the capstan and flywheel  bearings, make sure also when in stop mode, when motor is disengage, that their is 0.3mm spacing from motor pulley to rubber tire, their a spring scale adjustment in front of the motor, make sure that the capston also turns nice and smooth and torque is within specs, If any of this fall unacceptable levels range, quartz lock system to continuous adjust speed, which may cause a pulsing noise, also check all ground point where the screws hold the board in.

Also check the surface of the tire.

Hello Retrodos!

wich IC should i buy?

wm d6c with serialnr:13775

and my husbands serial beginns with a 5?

and wich generations is mine d6c and wich generation is my husbands?

For serial 13557 uses CX20084, now for the one that start with 5, really depend if it's a 6, or 5 number longs? Now only needed if it playing to fast, or issue related to the servo?

Checked the system mechanically. All rubber is perfect, the rest of the mechanism is good and brand new as far as I can tell. Not a grounding board to chassis (screw) problem.

Now I need to figure out how to test for problems on the transistors. What Procedure did you do to test for defective transistors?

I've checked online and IC601 for this revision D6C CX609A seems to be harder to obtain than the CX20084. Do you know a good source for this IC? Besides CX069A, could the problem also lie in the separate comparator NJM2904V?

I can provide a sound file of the hum in question later, see if it is identical to the hum you had in your D6C.

Upload the audio file

Listen to both and did notice the newer revision d6c does have a noise to it, when volume is turn up, not really a hum, more like amp hissing, that the older D6C doesn't. So may be within the design itseft, as the one I try was NIB, but notice it on the one I replaced the caps on to. But the older one sounds clearer.  

Audio file, D6C Rev.4. No tape. When music is playing, hum cannot be heard as the music is much louder.

Seconds:

0: Vol 6, Normal, No Dolby.

4: Vol 10-0-6.

10: Cr02/Metal. (hum is reduced.)

15: Normal.

20: Dolby C. (hum is heavily reduced.)

25: Dolby B. (hum is reduced.)

30: No Dolby.

35: Speed tune on (hum follows motor speed.)

50: Speed tune off

See if this is similar to the problem you encountered.

It's normal, all stock d6c's has that low pitch sound, even the d6 has that sound, reason why my older d6c sound cleaner is due to upgraded the OP-AMP line amp IC301 from a NJM4558M to a NE5532,  improves sound quailty, it is noticeably improvement, but haven't try this mod in the newer revision d6c. The 5532 consumes about 7-8mA vs 2.5-3mA for 4558 about 5% more battery power. The headphone amp is downstream from the line amp, so changing the line amp did improve the headphone sound, but the headphone amp IC's will still be the limit. I haven't found a pin-compatible op-amp to make it easy to swap out. But did use modern single op-amps, but had to make circuit changes to set the gain and re-wire the mismatched pins, did it to mines no noise can be heard and sound improved. Also did other mods to it. Only limit is the head.

First revision use the better core, better board layout, reason it was modded.  Newer revision haven't done mods to it yet. So can't help you now, as have to look at the block diagrams first, they may have used a different design after 2001.

Last revision is good if you want one with lower hours and recommend to most, only because they are less likely to have issues with rubber and capacitors. But for serious listening go with first revision, just make sure you find one that hasn't been used, then mod it as rubber, gears and head will be not worn.

I can confirm also that my 27xxxx D6C has that low level high pitch sound too. Hardly noticeable with Dolby C on, much more noticeable without any NR.

That is quite disappointing to hear. All the while I thought this was an issue with my 2 D6Cs. This D6C sounds absolutely sublime though. Do note that my older 2nd revison D6C has this hum too, but is of a lower level. I might want to investigate this.

I don't tend to use NR for recordings for the sake of compatibility (Tape stock, other walkmans, etc.).

Retrodos,

Does your modified 1st Revision D6C have less hum than your newer ones? If there was a way to modify the D6C to eliminate this issue, that will be fantastic.

Plop,

Interesting you have this as well. So it is a trait of the D6C.

Do you know, sony d6C with serial #42160 required CX20084 or CX069A? I found one with double-speed problem and need to decide to buy or not to buy. As I see CX069A not possible to find...

cx20084 broken

I know this is old but the deck and it's problems still exist. I have a WM-D6C that has a new CX20084 in it as the other was toast and the speed even when adjusted correctly- when the jumper is soldered- the crystal control is working the speed is about 1 percent slow. It has been oiled and I have been looking at the crystal control that put out the signal on pin 5 but it is not clear how it affects the ramp signal of the servo chip. It does lower it though. moving the frequency with various caps at the crystal would not work as the move would not be large enough. it seems like anything I have tried does not result in a positive move that is stable. The experiment goes on. I have worked on many of these but am learning that some people want them modified and other things done which is spoken about but no details are ever given.

The IC's are available from China and my last order was for 12 of them- two used already.