Sony WM-D6C and DD Series Walkmans - WARNING! Read this before plugging in any DC adaptor!

As regular readers of this forum will know, most Sony WM-D6Cs have a serious design weakness, which is the use of the CX20084 motor servo IC (IC601). This IC is very easily destroyed by use of the wrong power supply.
I say “most” D6Cs because the very last ones to be built, between 2001 and 2002 were re-designed to use a different motor drive IC.

The CX20084 controls the speed of the motor, and therefore the tape speed. If the CX20084 is damaged the tape will run very fast.

Until early 2020, it was relatively easy to source replacement CX20084s, however, since the start of the COVID crisis, they are becoming very hard to get hold of and very expensive. This is why it is more important than ever to look after your CX20084.

In summary:

• Do not plug any mains DC adaptor into a D6C.
• Only power the WM-D6C from rechargeable batteries (which deliver a lower voltage than alkaline batteries) such as Eneloop Pro.
• Most adaptors which are sold on Ebay as “suitable for the Sony WM-D6C” are not!

Why is the use of the CX20084 a problem?
The CX20084 is connected directly to the incoming power supply, either batteries or external supply, with no protection at all. Worse still, it is connected all the time, even if the D6C is switched off. If you plug in an incorrect power supply and realise your mistake before pressing play, FF or REW, it is still too late. The CX20084 will have been damaged. This also applies to DD series walkmans which use the CX20084.

The CX20084 can be destroyed by use of any of the following:

• Reverse polarity power supply (it should be centre negative)
• Power supply delivering over 6V (including a fresh set of alkaline batteries)
  
• Switch mode power supply

Most power adaptors are wired centre positive.
If any power supply with the barrel connector wired centre positive is plugged into the D6C it will destroy the CX20084 instantly.
Centre positive is the most common configuration in use but Sony used centre negative on some of their products, including the D6C.
Most power supplies sold on Ebay, including many specified as “for the WM-D6C”, are centre positive.


Is a 6V B+ supply too high for the CX20084?
Although I have never seen a datasheet for the CX20084 (and I am never likely to see one either), I think that 6V is at, or beyond, the upper limit for the allowable supply voltage for this chip.

The CX20084 is used on many other DD series walkmans, such as the WM-DC2, WM-D3 and WM-DD100 where they are powered from 3V, and is generally very reliable as long as they are not subjected to a reverse polarity or switch mode power supply.

I have had a couple of cases where a CX20084 has been destroyed by the use of alkaline batteries – a fresh set can deliver 6.4V.


Sony “6V” plug top supplies – may be higher than 6V.
A customer in the United States has a few of these and tested them with his Fluke meter. The results were an eye opener. The voltages you see here are the voltages which will be applied to the CX20084.







Increased use of switch mode power supplies.
The WM-D6C was designed in 1984 when plug top supplies were mostly of the linear type. These deliver a smooth regulated voltage. By the late 1980s, with the growth in home computing, switch mode supplies were becoming more commonplace. These are smaller, cheaper to manufacture and more efficient. Throughout the 1990s and beyond, switch mode supplies became the standard.

The downside to switch mode supplies is that the DC output side is not totally isolated from the incoming mains. There is a class Y capacitor connecting the primary and secondary sides of the transformer, which provides AC coupling. This is to suppress RF interference. This results in a common mode high voltage (up to 290V Pk-PK in the UK) low current signal on the DC output plug. Because of the very low current it won’t produce a noticeable electric shock but it will destroy a CX20084 instantly.




WM-D6C redesign in 2001
By 2001 portable digital recorders were becoming smaller, better and cheaper so the cassette format was starting to become obsolete. Then Sony did something rather surprising; they re-designed the D6C so that the motor was controlled by the CX069A chip rather than the CX20084. The CX069A is an older chip which was used in the WM-D5 series portable recorders in the late 1970s. The new D6C motor drive circuit was similar in many ways to that used in the WM-D6.

Why did Sony go to the expense and trouble of re-designing the main circuit board for the D6C when it was nearing the end of its production life? A very high failure rate on production test or during the warranty period would have been a good reason to do so.


Solutions
Since replacement CX20084 chips are getting very difficult to find, it is more important than ever to protect your working chips, so how can you do that?

The simplest solution is to only use rechargeable NiMH batteries to power your D6C, such as Eneloop Pros. A fully charged set of these delivers around 5V which is less stressful on the CX20084.

For a more practical solution, I have been working on fitting a small 4V regulator to the unswitched supply to the CX20084 and motor drive transistor. This will protect the chip against over voltage and reverse polarity supplies. I will provide a more detailed write up in a separate thread.
Of course this won’t fix a CX20084 which has already been damaged, but it will provide a layer of protection to a working one.

 

Thank you for the warning and a very detailed explanation Deb64!
ive got a same model and everything is still works well accept it doesn't rewind ( makes noise if I press rewind button?) )

I've got the original Sony power supply that is huge and heavy.. was wondering if there is a lighter version possible or should I stick to the original?
another question ..how do I know what year my Sony wm-d6c from?

thanks
Vintagefreak

 

If the D6C doesn't rewind, the lever on the rewind mechanism is probably stuck due to hardened grease. This is a common problem on D6Cs.

The huge and heavy original Sony power supply is probably a linear power supply, which is the better type. However I would only use it with the D6C if it is the original supply which has been used with the D6C before. If you have not used it with a D6C before then I would not do so now.
That said you should check the output voltage (as the voltage regulator can fail) and make sure the plug is wired centre negative before plugging it into a D6C. Better still, use rechargeable batteries which deliver a lower, safer voltage.
If you get a lighter power supply, it will probably be a switch mode type which you should not use.

Unfortunately it isn't that easy to tell which year the D6C is from without opening it up. Sony changed the Dolby sticker on the back from silver to black in 1988. The mostly surface mount type PCB was introduced around 1994.

 

thank you for your reply , I should probably open the D6C ( never done that yet !) and see what needs lubrication and or replacing ... if I press rewind button I hear a buzzing noise.
about the power supply - it should be original Sony but purchased in Switzerland maybe in 80s or earlier 90s I guess.. I got it as a present 20 years ago.

best regards,
Vintage freak

 

@Mister X I think this thread should be made sticky, as it contains all the relevant information and a good title.

@Deb64 Great thread ! I think inserting a link here to the regulator thread when you create it is a good idea, so it becomes more visible.

@Vintagefreak There is already a thread covering the no FF/REW problem, so please read that and post there if you have addtional questions, as it would be best to keep this thread clean and only with info related to the CX20084.
No FF/REW thread: https://stereo2go.com/forums/threads/sony-wm-d6c-no-rewind-ff.4687/

 

thank you Valentin, appreciate it.

 

What do you think of using a good lab power supply and set it to <6V? Would that be safe or is there the same problem there as for switching PS? I've been using that when repairing walkmans, very convenient as you directly also see the current drain but considering the situation I might stop using that if you think it is unsafe.

 

And beware of sellers on e-bay claiming they are selling ''AC Adapter for Sony WM-D6C WM-D6 Professional Walkman Recorder Power Supply Cord | eBay''
this one blurred the pictures so you can't see the polarity.
https://www.ebay.com/itm/162267295911?

 

@Rune Lindman the bench power supply I use is fine, however, before using one for testing a walkman, I would check the output for common mode high voltage AC signals.

 

I currently use Duracell rechargeable and original DC6 and D6C adaptor, but I am interested in the Eneloop rechargeable. It looks like a quick A/B/C of three battery's packaging shows that the Eneloop Pro in 1.2 V, 2550 mAh, the Duracell in 1.2V, 2500mAh, and the Energizer PowerPlus in 1.2V, 2300mAh. This means the Eneloop is a longer lasting batter, correct?

 

Yes, the Eneloop will last longer. Alternatively, check out the IKEA LADA, for a fraction of the Eneloop price. Others have gotten quite good results, comparable to Eneloops.

 

I just picked up some LADDA 1900 and 2450 batteries this afternoon. So far so good, plus I have to say, I usually don’t care much for ikea’s actual design aesthetic, but these look good in a Sony player I have with a missing battery cover- way way way better than the Duracell. Thank you for this! You saved me quite a bit of money. If we ever meet, drinks or snacks on me!

 

Does anyone use 1.5v AA usb rechargeable batteries for DD series walkman?
Batteries are limited to 2A currents

 

I use Jugee branded batteries in my DD33 and they work fine. Only thing is because they supply a constant 1.5 V when the battery is too low, they just cut off. This makes it impossible to tell when the batteries are going to run out except for estimating based on how long you have used the walkman.

 

The LED indicator on these Walkmans is not reliable anyway @Walkmanlover . Except for the 5 bar D3 perhaps

 

For me it is. When I use regular AA's and the LED is hardly visible outside the batteries need changing. Otherwise if the LED is bright it means the batteries are good.

 

Hi Deb64,

A good writeup, I'm surprised to hear of Alkaline batteries overvolting a CX, I have never run into this issue because I hate Alkaline batteries with a passion due to the leak damage they do to our prized WM`s, however I couldn't agree with you more on not using wall wart power supplies, even the linear ones are rubbish, they may say 6V, but most aren't regulated and are reliant upon the load sagging them down to their advertised voltage... plus why trust a $20 dollar item to safeguard a $2K item...
I have even considered disconnecting or blanking off the AC adaptor sockets for future proofing reasons...

This brings me to the next logical thought...
Would be good to have a small think tank on how to design an aftermarket replacement daughtercard for the CX using a programmable IC...

 

It depends on what your definition of a good lab supply is.
I've seen "good lab supplies"- switch mode ones especially, do some horrible things.
I would treat a CX chip like I do my WW2 German valves- use only a linear supply, regulated to the right current and slowly ramp up the voltage in steps to around 500mV less than they were designed for on the heaters and tens of volts lower than their spec`d plate voltages... maybe I'm a bit to precious with them but hey, I don't want to find out the hard way I wasn't!

 

Great advice, I've owned quite a few D6C's and today I have the D6 and a newer D6C, third gen I think.
I take the opportunity to leave an alert about rechargeable batteries. Those that offer 1.5V are theoretically wonderful, they never change from 1.5v because they are internally regulated, in fact they are 3.7v with a step down. The problem is when there is a problem, if the regulator stops working when it is well charged and in use, the 3.7v goes straight to the device. This happened with 2 of my batteries, fortunately, they were in equipment that suffered no damage. But I imagine that if that happens in D6, it would be a disaster.

 

3.7V Internally? The Li-ion might be, but the NiMH batteries like Eneloop Pro and IKEA LADA I don't believe are.