Chasing the Sony CX20084 speed chip for D6C walkman

My part

 

Man, if I had just seen this highly informative and important thread before using an AC adaptor with my mint low use WM-D6C that I bought some years back, it would still be working right. Yup, most likely fried the CX20084 when I plugged it in, as the D6C started running too fast shortly after, the speed control having no effect. I have a quick question: Who in North America and in Europe / UK, repairs these units and currently takes new customers? In fact, is there anyone who has gone a step further and managed to recreate the circuit using discrete components as an alternative solution (instead of the problematic CX20084) with some protection in place so that even plugging an AC adaptor with the wrong polarity would not harm the unit? I would like to explore the latter option. Again, fantastic info, thank you to all the contributors.

 

You might want to contact @Deb64. The only way to continue for now is to salvage the chip from another unit, here are a few if I remember correctly: WM-DC2, WM-DD2, WM-D3, WM-DD3, WM-DD30 [not WM-F200, WM-F202].
(I have a DD2 and DD3 that I can part with, although they look to good to me to rip apart just for the IC.)

 

@Emiel Thanks very much for the info. Yeah @Deb64 and also @Valentin are some of the top names that pop up often, talented people for sure.

 

@Emiel When sourcing some of these players for the IC, there's usually some cheaper ones described as for parts, not working or junk but how is the buyer to verify if these non-working units have a good IC or whether or not the IC has been already taken out, when buying from online sellers? Any advice?

 

The best way is to buy a DD unit that is in very bad cosmetic condition, but does still power on.
In the vast majority of cases DDs have been used on batteries, so the chance of a bad IC are minimal, despite not 0%.
There's no way to know for sure if the IC has not been taken out already, but chances are low.
If someone has already taken that IC out, they have probably kept the unit for taking other parts, not sell it online.

The F200/F202 have a different servo, so those can't be used as donors.
What will work as a donor unit are the following units: WM-DDII, WM-DDIII, WM-D3, WM-DD30, WM-DD1/WM-DD10/WM-DD11.
There are others from the DD series which this IC, but these are the ones to be considered as far as reasonable price goes.

 

Thank you @Valentin much appreciated.

 

Shoot, I made a mistake with the list. The CX20084 is next to the CX20123.
That is the servo IC in a lot of units (not DD), usually indicated by the traditional IC601.
Think of: Sony WM-10 and WM-30 Serial No. 77001 and later, WM-40, WM-100, WM-F200, etc.
I am working on making some of these overviews available on Walkman.land, progress is kind of slow.

 

The CX20123 was used in the WM-100 and WM-200 series as far as I know, while WM-10/20/30 series use a discrete servo circuit built around a NJM2901 comparator.
Then at the WM-500 series, when they switched to a normal DC motor instead of the 3-phase brushless they used before they also swtich to the generic AN6653 servo IC.

 

Take for example the WM-10II / WM-30 - up to serial number range 77000 it is the NJM2901B, above the CX20123.
Not sure what a Servo Circult is though

 

Sorry if this was answered before but as the genuine CX20084 chip is no longer available or at least extremely difficult to find (other than to cannibalise some Walkman models mentioned above), does this necessarily mean that all so called "fake" or copies of this chip are useless? I ask because I have done some looking around the different chip makers around the world online and found that some do stock this chip and I have even inquired about it. I'm not saying they're genuine (highly unlikely) but is that important if in fact the copies do work as they should? Some may, some may not, maybe depending on the company, and looks like some of those places are legit, have many years experience making chips. And would a chip like the CX20084 be a challenge to duplicate by a good experienced company in the field? No doubt some are better than others, but I'm just asking.

 

I know there have been made good copies in the past. but ask yourself if it's not better to get an old DD11. Yesterday I bought a DD11 for 35 euro, its containing the original chip.

 

That is an option for sure but not a solution to the issue at large. Plus the fact that these DD Walkmans rarely go that cheap and no one can be sure that the chip is still intact or functioning correctly. It's very risky and you end up paying for it. The most ideal solution is to find a reliable source of these chips, even "copies", which shouldn't be that hard to make for a legit chip manufacturer.

 

You saw this post for the tester? https://www.tapeheads.net/threads/t...tor-chip-tester-by-using-wm-d3-wm-dd11.98705/

 

Yes, thanks, saw this before but, again, not sure if this is a viable option for most of us. Wouldn't it be a good idea to vet the good potential IC's by just asking manufacturers / distributors / resellers for certifications and testing results of these chips, including detailed datasheets etc etc..?

 

Design and create a chip like this will cost 100 of thousands of dollars.

 

The D6 is looking better as time passes. The potted or hybrid modules this release used for muting, Dolby and speed control can all be repaired and placed back on the PCB. D6's also had the v shaped amorphous head. Buying a D6 with issues is a safer bet than buying a D6C with speed issues I'm thinking and they do a great job hot recording onto quality type II and type IV cassettes.

 

I have a quick question to everyone: When you look for poor condition models for their CX20084 chip, especially on eBay or when you can't test yourself, how can you be assured that the chip is still intact and working correctly in those units?

 

Think this question was asked before. What you say isn't really that big of a concern in practice because:
- a donor D6C you just won't find at a good enough price, even if it's in non-working state. So this is not a potential donor to begin with.
- DDs (DD10, DD11, DDII, DDIII, etc.) are almost always used on batteries, so the chances of IC being bad is just very low.

The only way to tell for sure is by asking for a video, to see the actual takeup reel spinning and judge if the speed is normal or too high.
Of course there is some risk involved, but you have to take it.

 

Thanks @Valentin I was of course talking about the other models you mention, the DD's ..... It had occurred to me that since a bad CX20084 shows symptoms (at least on the D6C) including the motor running constantly when batteries are inserted (no buttons are pressed), wouldn't it be a good idea to ask the seller (of a DD unit) to insert some batteries and (without pressing any buttons) listen closely to whether or not the motor starts running. If it does run then likely the IC is bad. If the motor doesn't run when batts are inserted but starts to run when play is pressed then likely it is OK. If I'm not mistaken a bad CX20084 IC main symptom is usually the motor running when batteries are inserted (but no buttons pressed). Is it the same on the DD units? Can these test be performed (even with no cassette inserted) with the the other DD models? That way it doesn't really matter if the spindle turns. All we're doing is listening for the motor run.