Chasing the Sony CX20084 speed chip for D6C walkman

Chasing where to buy genuine Sony CX20084 x 2 chips.

Do the fake ones work ok or do I need genuine?

I have 2 x Sony D6C that sound like chipmunks

thanks

 

I bought chips on eBay I thought were genuine. Sent them to @Deb64 alongside my wm-d6c. She told me they wouldn't work. Luckily she had some in stock.

 

Ah now I'm wondering how many fakes there are out there. I bought a strip of 6 several years ago. All faintly labelled Sony CX20084. How do we spot the imposter without actually going through the pain of using one to repair a faulty D6C and finding after all that effort it doesn't work?
B

 

@Silverera Please post some pictures with your chips.

 

Had trouble logging in for some reason.
Anyway @Valentin image of Sony CX20084 IC's purchased 5 years ago on eBay. Can't recall where they came from.
B

 

Ok, there are some tell-tale signs that the chips in your picture are fake:
- the fact that they are packed into SMD tape and reel; it's hard to say if back in the day they were packed like this for assembly or not, however the ones that I have seen for sale and are genuine were never sold in such packaging;
- the font color used on the IC is a dark gray, while it is whiter on the genuine ones;
- the SONY logo font is different than original (letters are more narrow);
- the pin1 marking on the package looks spherical on the genuine one and flat on the ones in your picture;
- there is no date code; should be composed of 4 digits like 8911, meaning 11th week of 1989; we only see 3 digits on these;
- we can probably find even more differences, but there are enough for me;
- the most obvious one is the different color/font and the lack of a date code;

I attach 2 pictures of genuine ones below. The older one (date code 8911) is what was installed from the factory in most older D6Cs/D3s/DDs. The "N84" at the last does vary, especially between D6C and D3/DDs.
The newer one (date code 9169) is what will be mostly found today for sale, while the older ones without SONY logo are rarer and harder to find. Even the newer type has become pretty rare these days, but it's not impossible to find one.

EDIT: Further digging suggests the newer D6C with SMD PCB does use a servo IC that looks very similar to what is depicted above. It has a different format date code most likely and the font/color is also different than the 2 versions I have shown.
That is why the only 2 types that I would consider are the ones shown below. As for the ones in picture above, there's just no way to tell if they're genuine without soldering them and testing. Of course, it is to be mentioned, just working is not enough.
Wow&flutter must be within the specification of 0.04% WRMS (0.05%-0.06% can also be considered good depending on test tape used). If it's 0.15% (assuming PLL is connected), the chip is clearly fake even if it works.

Do you remember how much you have paid (approximately) on those ICs ? I almost bet it wasn't much.

 

Best thing to do is buy a cheap dd series and desolder the chip from the board and place it on the D6C, thats how I do it when I need a chip. I tried many fake chips but almost all failed.

 

When these IC's arrived I thought maybe they're some cheap knock off and badged "Sony". They were not overly expensive but I can't recall how much they were as they were bought around 5 years ago as insurance if my D6C's ever needed them.
Still we need to find a source of the genuine ones and soon I would say as these IC's will eventually disappear like the one in the D6. No longer available.
Perhaps @Deb64 could advise on a reliable source of supply.
Thanks @Valentin

 

Unfortunately not. These are getting really hard to find now.

 

Well I guess you can always strip down the defective CX20084 like we did for speed control IC in the WM-D6.

 

@Silverera The CX20084 is not a potted hybrid module, so there isn't anything to strip down. If we are to do that (assuming we could do it without damage to bond wires and the die itself), there is still nothing that you can repair at that level.
Inside the package you will find something like this (keep in mind CX20084 is much more complex than the op amp shown here): https://www.righto.com/2018/06/silicon-die-analysis-op-amp-with.html , which can only be used for reverse-engineering the circuit.

I only see only 2 solutions long-term, as the stocks of these chips is nearly depleted at this point in time:
- taking the IC from a donor DD unit (what @tomtom87 mentioned); however this greatly depends on 2 factors: how cheap that DD can be found and if you need other parts from it (if you do repair on a regular basis, there are other useful parts).
- reverse engineer the circuit and make another based on discrete components, op amps, comparators. This altough not impossible to do, will require a much bigger footprint than original IC and a different PCB fitted somewhere else in the walkman, connected with wires/flex cable.
This second option is very unlikely to happen and I'm not even hoping at it, given the complexity of the circuit. Then we must realise the market for such ICs is not that big, otherwise we could re-design the entire PCB and keep just the CX20218 Dolby ICs.

That's why it is very important for people who own a D6C to forget using any mains power adapter (plug is center negative for those reading that do not know) or even alkaline batteries (which are not that economical or ecological to use anyway).
Unregulated mains adapters will have a much higher voltage when not loaded (like 7-8V instead of 6V) and the Vcc of CX20084 is connected directly to the plug, without a switch (so it is constatnly exposed to the battery/DC in voltage).
Then, even regulated ones will have a high common mode voltage, so in my opinion just forget about using one entirely. So keep in mind that fixing you D6C will become much more expensive in the future due to this mostly unobtainium part.
The power consumption of these devices isn't really that high and using high capacity NiMH batteries will make it run more than enough. Something like Eneloop Pro or similar high capacity NiMH batteries are the best choice for this walkman.

 

I second what Valentin has posted.
Especially his third paragraph on the importance of taking care not to damage existing CX20084 ICs.
I, too, recommend only using rechargeable NiMH batteries such as the Eneloop Pro to power a WM-D6C.

NEVER plug any plug top DC adaptor into your D6C*, even if it was sold as "suitable for Sony WM-D6C". There are plenty of cheap switch mode power supplies for sale on Ebay for the WM-D6C which will destroy the CX20084 as soon as it is plugged into the walkman, even if you realise your mistake before you press any buttons or switch the walkman on.
Even if the polarity on the DC plug is correct, a switch mode supply (which virtually all plug top supplies sold these days are) will destroy a CX20084. So far I have had 3 walkmans in for repair which have been damaged by switch mode supplies.

*This also applies to the WM-D3, WM-DC2 and WM-DD100 and several other walkmans which use the CX20084 IC.

 

The Sony WM DD11 also uses this chip. Serviced mine yesterday and noticed this. Very conveniently also named 601 (just as in the D6C). Enclosing a CU of the schematic.

Edit:
Yes, and I'm also hunting the elusive chip. Posted a couple of enquiries today at e.g. Utsource.
https://www.utsource.net/de/sch/cx20084.html

If anyone has one for sale, please mail me at jacob [at] jacobstalhammar.com

 

It seems preservation is going to be the norm with all of those treasures. D6C DC2 and DD100 which most long term collectors will have. Agree about using batteries. Good NiMH AA cells work well for recording on D6C's and last for several hours in that mode and many more in playback. I am going to ditch my after market AC adapters for all of the above Walkman. Seems you can assume they are all cheaper switch mode types. Great thread guys BTW and I hope we have saved our CX20084 for many years ahead
B

 

There are even sellers on ebay which sell the walkman together with such a switch mode power supply, so buyers beware. For referece, all DD models except WM-DD, WM-DD33 and WM-DD9 have a CX20084, so all except those are suspectible to the problem as well.
The fortunate part is DDs tend to be used only with batteries, so it's a much rarer problem on those, but it's still something to be aware of.

Unfortunately, at this point in time, most people are still unaware of this issue, that's why it might be a good idea to create a sticky thread about this.
@Mister X what do you think about this ? Maybe this one (https://stereo2go.com/forums/threads/d6-with-issues.6205/) would be a good start, although it treats both D6 and D6C (but it's better than nothing). Or we start one from scratch.

@jacobsteel Most of these DDs have one (exceptions listed above). As for that utsource part, I have seen it before, but given the very large stock they display I have reasons to believe it's not the genuine one. Have not used that one so cannot say for sure.

@Silverera Yes, all modern consumer power supplies are of switching type for efficiency reasons (>90% efficiency compared to ~60% in a linear one). They are also required to have very low standby current (by regulations such as EnergyStar), which only switching ones are capable of.

 

While I have a working DD11 and theoretically could A/B test my D6C; solder/resoldering of surface mounted components wear on the circuit board and cannot be performed that many times....

thus I thought of a third option;
There is some space behind the main circuit-board on the D6C (above the DC/DC regulator). I ordered a simple regulator board (at least it appears small, picture enclosed). I might try - just as a proof of concept - reconnect just the motor to the regulator board via switched 6V. This could well bring down a static voltage to an acceptable level - however, the speed regulation would of course be missing (as nothing reads of the coils anymore).

If I perform this experiment I can post the results here. Theory: the first Walkmans used similar motors, these motors were very good and produced decent results even without the quartz lock.
Fully aware this is a sub par solution, it might revive my D6C (which works perfectly in every other respect). An additional board would do minimal damage to the main board which later could be restored with a CX20084, should I ever find one.

@Deb64 - have you tried anything similar? (and/or would you have a CX20084 for sale? I got some replies from the Component services... but as you mention, some seem really dodgy).


Also
A theoretical fourth option (a variant of the second actually) might be to use an Arduino.
To make space you would have to rebuild the D6C to only use two batteries. Use this space to house an Arduino reading the coil frequency and stabilize to a motor output transistor. You would need a micro DC/DC converter* to up 3 V to 6V as well.
Battery life would likely suffer, even if this is theoretically doable.

*https://se.rs-online.com/web/p/non-isolated-dc-dc-converters/1736942?cm_mmc=SE-PLA-DS3A-_-google-_-PLA_SE_SE_Power_Supplies_&_Transformers_Whoop-_-(SE:Whoop!)+Non-Isolated+DC-DC+Converters-_-1736942&matchtype=&pla-335000711026&gclid=CjwKCAiA3L6PBhBvEiwAINlJ9ONynyB3vroISDIZ_rGX7EWeU4YgFzXJhliZyglHZuzAumV1ZF5Y1xoCS8AQAvD_BwE&gclsrc=aw.ds

Incidentally, while the CX20084 was not available from Sony, some D6C parts were: https://sony.encompass.com/item/556372/Sony/8-759-909-45/

 

@jacobsteel Unfortunately the third option proposed by you is something that will not work in practice for a couple of reasons. Let me explain further: even the most basic cassette tape player has some kind of motor governor, meaning the motor speed is regulated to be:
- independent of load (you get load variations as tape spools, load variations depending on position of walkman, load variations depending on beginning/end of tape); this is a must have, otherwise, wow&flutter will be all over the place and you just cannot obtain a stable speed;
- independent of battery voltage (this can be achieved by a regulator, however a linear one would be more appropriate since the switching type has a lot of high frequency ripple and depending on topology it will also have some low frequency ripple);
- independent of temperature (the walkman should work similarly at room temperature as it will work at 0 degress or lower); there needs to be a mechanism to compensate for this and most regulators don't have one because they're not voltage references;

There are 3 basic types of motor governors:
- the most simple and widespread is one that takes a feedback signal from measuring the current of the motor (higher current means higher load);
- the second type is what SONY used in its first walkman (the TPS-L2): a motor that contains an FG coil that picks up the speed of the motor shaft directly: it's a much more accurate feedback mechanism, but it's the motor speed that is regulated, not the capstan speed;
- the thrid type is the one used on DD (a more complex direct drive system is used in DAT, VCRs): there is an FG coil directly on the capstan to read the capstan speed and adjust the motor speed accordingly;

Without the closed loop feedback mechanism, wow&flutter will be unacceptably high. As for the quartz lock, the D6C and all quartz lock units will work with it disconnected (there's a pad on the PCB for that), but wow&flutter will be higher (in case of D6C significantly higher).

Arduino looks like an interesting option, but creating a digital feedback loop (suppose we read the FG signal with ADC<which is not a good idea as it's slow> and output PWM to the motor) will add signficant delays in the system. It can be done, but you need a really fast processor to be able to do the "correction" in real time.
A small FPGA or a high speed microcontroller (with fast clock like 80-100Mhz) might be the better solution in this regard, however even that will have a significant footprint (likely larger than an analog discrete SMD circuit) and will require a properly designed firmware to run well.
And then there is the solution of making a fully discrete circuit based on transistors, diodes, comparators and op-amps. It doesn't have to be identical to original, but it would be prefferable to be a plug-and-play replacement.

In reality, despite the fact both microcontroller/FPGA and discrete are solutions that can be done, they're not that easy to implement. And then you have to consider the cost: if I were to design such a circuit and sell it at 70-100euros (without any profit), would it really be a better option ?
Fortunately, those CX20084 can still be found to some degree: usually the genuine ones cost 40-50 euros/pcs, anything lower than that would indicate a fake. And then there's the donor DD option, especially that some damaged ones are available at prices lower than 100 euros.

 

@Valentin - you are entirely correct in that wow and flutter will be significantly higher on all "free running" motors (regardless if a static current is controlled or not).

And thank you for the heads up!
I wasn't aware the TPS-L2 had a feedback loop. Thank you!
I didn't bother looking it up before guessing. My bad. But, I checked it out now. Interesting (and, again, the controller is named IC 601. Detail below).


From my other vintage tape-recorders I've noticed several degrees of variation;
The Nagra III (video: bottom) has a magnetic-read (cogs) feedback loop (similar to Revox A77 and not entirely unlike the later Sony variants) the motor shaft is the capstan. Extremely stable (but - as you say - measurement is done at the capstan, in direct mechanical contact with the tape).
The 50Hz AC tape recorders (video: left) are stable (but not easily variable). They often sound OK, but cannot be carried around and keep any stability.
And, the older battery operated 1/4" (belt driven or rubber-disk driven, video top and right) are very variable. Basically wow and flutter generators. The simplest ones don't even have a capstan-pinch-roller system at all (only direct drive to tape platters).

In fact, I used some of this variation here (although, as they are all playing tape-loops, extremely fluttery):



EDIT: ... and I just got mail from Utsource. They didn't find it.
"Thanks for your inquiry , we checked our stock, but regret to let you know so sorry no parts.If any other new inquiries, you can browse our website : www.utsource.net"

 

@jacobsteel I have a BASF HiFi 8200 deck in my collection (which has some problems, I have not bothered to fully repair it). It has an AC motor (powered by a step-down transformer) and the wow&flutter does seem ok by ear (although I admit I never measured it).
However the motor on that one is very big and it also has a massive flywheel (I think 300grams at least). There are even mechanical governors that exist on older tape machines: have seen on another thread on the forum, but can't remember which one at the moment.

As for a potential repair for the D6C, in a worst case scenario there is a very simple solution: design a PCB for a SMD AN6612 (very common IC used in many walkmans and portables), as it requires very few external components and bypass its own servo and FG entirely.
This will probably get you a wow&flutter of 0.15% WRMS (which is decent, but nowhere near original spec). You can even make the auto-off function work, as something similar is implemented in the Marantz PMD430/221 and its relatives (all use AN6612).
So there are compromise solutions, it's not like these devices will go to trash once CX20084 is no longer available, but the above solution is a compromise as it won't have the original performace.

As for the most stable tape transports, those are by far the direct drive ones with multi-phase motors, like those used in DAT and VCRs. In digital recordings, accurate tape speed is even more critical, as there is a limit of errors that can be corrected.
But those are a lot more complicated, as the head drum speed must also be very accurate and also in sync with the capstan rotation for tracking.

In regard to the Utsoruce, that was to be expected. If they really had 30k pcs in stock, there would be absolutely no problem. At this point in time ebay/auction sites are the only place you can probably get such an IC and many sellers only have one.
Of course everyone does that at their own risk, I will not recommend any specific seller in this regard.
There was a seller from Germany on ebay last year which had about 30pcs in stock (all genuine) and all of them were sold. I almost regret I did not stockpile, but in reality I wouldn't have used more than a handful of them.