Chasing the Sony CX20084 speed chip for D6C walkman

Unfortunately I don't have any spare CX20084s available for sale.

Regarding regulators, yes I have developed a small regulator to protect the CX20084 and motor drive circuit and I have fitted it to several D6Cs.
I'll start a new thread with the details but the regulator delivers 4V. The CX20084 can operate from a 3V supply and the motor is rated at 2.5V so the motor drive system does not need 6V to operate. The regulator protects the CX20084 from over-voltage and reverse polarity. The system seems to work well. The most obvious difference between a 4V modified D6C and a standard one is that the modified version feels much smoother when running. Normally there you feel a slight vibration on a D6C when it is running but the vibration is a lot less on a modified one.

 

@Deb64 Powering the motor drive circuit through a regulator is a very good idea indeed. Of course, it implies a working device to begin with...
It is interesting that it runs much smoother: I have noticed high frequency variations on the wow&flutter waveform and I now wonder if that is caused by the supply of servo circuit being unregulated.

I think it's best that we ask @Mister X to make your upcoming thread sticky, since it will also cover the problem, not just the solution. I think using a suggestive title, like "Read this before using you D6C" or something along those lines is a good idea.
In my opinion it should be as many related keywords as possible to be found through Google search easily. A few of my suggestions are: SONY, walkman, D6C, buy, advice, speed fast, etc.
Of course these are just suggestions, there can be 2 separate threads one covering the problem, another the regulator solution. It is up to you to decide.

 

@Valentin - Good suggestion, thank you! I checked on the Marantz and that circuit looks quite simple (below).

@Deb64 - oh, I see. I must ask, have you tried any replacement circuitry? There should be at least some space between the DC/DC and the main board to place an extra board in?


Mainly out of curiosity (and as these boards are available on Ebay/Amazon at low prices) how would a PWM work? Or one of these "motor regulators"
frequently on sale. I guess they use an NE555 (some of them). Here's an example.
https://www.amazon.com/Sipytoph-Voltage-Controller-Adjustable-Control/dp/B095SWSX8M/ref=sr_1_3?crid=1YR321RWIDUZQ&keywords=6V+speed+regulator+electric+motor&qid=1643166491&sprefix=6v+speed+regulator+electric+motor,aps,123&sr=8-3

 

@jacobsteel Those ebay/amazon "motor regulators" do not have a feedback loop, so they won't work well at all (they probably don't output DC). I wouldn't even consider such thing as an option. A 3 transistor governor would do much better than that, if carefully designed.
PWM can work very good in theory if the duty cycle has a very fine control. However, there are problems with driving the motor with PWM. You can read this article: https://www.machinedesign.com/materials/article/21125511/controlling-brushed-dc-motors-using-pwm
Then there is the problem of needing a separate power supply, as the PWM will generate ripple and noise on the supply line that will get into the audio. Then even the motor itself can radiate electromagnetic field that can be picked up by head preamp or even the head and get into audio.
In practice, when you start designing such a circuit, you will realise there are a lot more variables that you originally thought, some of which may make the circuit unfeasible. The only real solution is to re-design a circuit with similar functionality as original (which would likely require ~20 transistors).
I mentioned PWM because in a digital system (like microcontroller/FPGA) it's easier to generate precise PWM than DC. DC requires a DAC and the micros that have a built-in DAC have a very large footprint. So a lot of external components that you don't want there.

There are even simpler solutions than the AN6612 one, as motor governors can be implemented with a couple of transistors and also include a current feedback loop. I can create a separate thread in the future explaining motor governors and servos (as this thread is already pretty long).
So you have many potential solutions, unfortunately making one that creates a wow&flutter even close to the spec would be pretty involved to do. Such a circuit would definetly involve using the FG signal and a precision reference (such as the PLL used in original one).
Please keep in mind that I personally would not implement such solutions (despite their easy implementation) because of the poor performance. These are just ideas of what can be done in an absolute worst case scenario, when we just don't have any ohter option but re-design the circuit.

 

Hello
reading all this it came to my mind when I was looking for an engine for my JVC KD-A7 ..... I was lucky to find the complete spare part .. in addition to the main and secondary engine also the fully functional control card ...
Motor ...Engine m1606-00A | Stereo2Go forums


this circuit has few components and the NEC 1003C2 chip ... This chip is old and there is little information on the net but I found that it was also used for speed control on some turntables ... Now I'm not saying to use this chip but I do not think that today there is no more modern substitute that can allow us to create a suitable circuit for our purposes ... much less expensive than the prices you see on the net for an original chip

 

@Silver965 Very good point ! This is a very simple circuit that seems to have everything integrated into one chip, including the drive transistor. What I don't like is the package is through-hole, so big.
But the idea is a good one and the picture made me remember something else: SONY TC-153SD also uses a system like this, but it's fully discrete (3 transistors). Wow&flutter on mine is ~0.12% WRMS with a new belt.

 

in this circuit however there are 3 connections for the motor and 2 for Fg ... (red White and another I think is the ground)

But now I try to look at the patterns I have

 

I need to double check, but I think the one going directly to the GND of the circuit is the motor shielding. Otherwise it wouldn't make sense, since the motor is grounded through the drive transistor (Q703) and the red wire is probably a direct connection to power supply.
Anyway, the circuit will need some modifications, I presented it just as a basic idea/starting point. Then there are other discrete designs out there, this isn't the only one.
I personally always prefer a discrete design, because such a design can always be made again with different parts than the original ones (if those become not available). Same goes with off-the-shlef ICs, like generic op amps for example.

As for the AN6612, I suggested that one because it's available in both THT and SMD packages and it's a chip I have seen a lot both in walkmans and portable recorders. I have even bought some for repairs, as that chip will also burn from reversed polarity.

 

And the Red that I don't understand what function it has ... for how it is connected ... on the capacitor ... on the diode and the wire that goes out of the circuit ... it looks like a check in case the motor stops but it is a negative looking capacitor 704 .... or reads a sensor mounted in the motor
An6612 and on some Aiwa models but I have not found a diagram with fg

I was wrong on that red wire .. i downloaded the schematic of the Tc-153 ... now or get it and a positive of 6 volts power supply the white and the negative controlled by the transistor and the third and a ground on the motor
@Valentin was right ... I didn't have a complete view of the circuit .... In my opinion it can be done ...

 

You can try to do this .. also the motor supply voltages are similar to the d6c ..




Only the resistances need to be recalculated R403 ..R404 and Th401 which are powered at 22 Volts

 

Hi Deb64, Valentin. You both have me worried. I own two Sony d-6c's that I bought back in 1985 and 1990. Ever since I bought them I have been using a Sony ac adaptor at home. I never take them out. Are you both saying that I should now stop using the adaptor altogether. I use the Sony
AC-D4M all the time and keep the AC-D4HG as backup.

 

@Valentin , @Silver965 , @Deb64 - thank you for very good advice!

Further testing proceeded with a really good cold-spray = No difference cold or "hot" = Further evidence that my CX20084 might be alright despite intermittent speed trouble.

Still, I did notice several persons before me had worked on the board. Thus, even thought I couldn't see any overflowing solder, or measure any shorts, I cleaned the board carefully. Alcohol with tops, very carefully.
And, every time I moved anything one of these small wires risked coming loose. So double and triple check the wires. All of them. And the voltages. Again.
Overall I noticed that the high-frequency circuitry is very easily provoked - and that both pots were quite worn.
High frequency noise may e.g. be a sign of an almost broken sleeve of the X-tal/AUTO OFF board cable (white center, ground/sleeve). EDIT: if the sleeve comes loose (easy if you service the mechanics below) the auto-stop and Xtal will stop working (the sleeve connects to the main board earth/ground close to "-" of C607).

Lessons learned:
• Even a not measurable short between legs 4-5 may provoke IC 601 to have the motor running at max.
• Hum induced almost anywhere in the high frequency circuitry may provoke a 3000 Hz tape to speed up to 4000 Hz.
• Broken ground connection/sleeve loose next to C607 = no Xtal power + no FF auto stop + speed jumps up.
= If you have trouble with your speed, check everything super super carefully.

Anyhow, 4 hours later, with the good help of you all, and Selma (picture), my old D6C has now worked well over 30 minutes without problem.
EDIT: I've now recorded a couple of records and it still sounds great. A very warm sound.

Knock wood, and thank you again for very good advice.

A speed governor thread sounds like a brilliant idea. Thank you! Selma says hi!

 

Hi Derek,

I would be very careful with the Sony power adaptors. If the regulators fail then the output voltage can increase.
Also, one of my customers based in the United States tested his Sony 6V power supplies after he had problems with a CX20084. The results were surprising. The lowest output voltage was 6.5V and the highest was 7.6V.
I would recommend using rechargeable AA batteries only (such as Eneloop Pro) as a full set will deliver around 5V which puts much less stress on the CX20084. Even a set of fresh alkaline batteries can deliver up to 6.4 volts which, I think, is too high for the CX20084.

 

Fingers crossed @jacobsteel. Hopefully you have found the problem. It is also worth checking the ESR of the electrolytic capacitors around the chip. You have a fine assistant there.

 

Hello
today I enjoyed designing the circuit that I posted yesterday
Note the measurements ... 33mm x 21mm ... actually very small ...
I did not consider making a hole in it to screw it somewhere ... as @Valentin wanted with discrete components within everyone's reach ... being a prototype I have not yet done functional tests and there are still a couple of resistors to be recalculated
I just wanted to see how big a circuit like that was

 

@Deb64 - Thank you! Yes, I love her so much (my dear cat, Selma). For some reason she loves the smell of soldering.

And exactly, I suspected the electrolytics around CX20084 first, so I changed them + the tantalum (around the FG input) and the two in the DC/DC. All measured out OK.
However, I've seen several capacitors produce correct values when measured with the Fluke - and then fail when in place. Tricky.

And, I must second the advice on adapters. Also, guessing away I would think along the lines of:
The D6C PSU connector has a negative center. And was used by a lot of musicians. The majority of guitar pedals use PSUs with the same type of connector, and a negative center, thus flooding the world with adapters. Guitar pedals commonly run on 9V, with adapters often producing 9-13. Perhaps a reasoning like "negative center, close enough" killed a few D6Cs.

 

@jacobsteel - The guitar pedal adaptor theory makes a lot of sense. 9V would be more than enough to kill a CX20084.
The capacitors which measure OK on the Fluke then fail when in place probably have high ESR (Equivalent Series Resistance). This is when a capacitor behaves as if it has a resistor in series with it. I've seen a few fail like this on the later surface mount type D6Cs; they seem to be a bit more prone to electrolytic cap failure than the earlier D6Cs. If you are going to work on walkmans, it is worth getting an ESR meter or Mtester.

 

At this point why not use a 5 or 6 volt regulation circuit type LM 7805 or LM 7806 and easy to install Example ... (7808) I mounted one on this circuit to get 8 volts

 

Not related to the D6C, but I own a WM-DDI (rubber disc), that is running too slow. It sounds like the motor is getting a very rough digital signal. It sounds like the speaker at the beginning of the movie Independence Day. Most people claim theirs are running too fast but Mine actually starts slow but gradually gets faster, but at its peak, it’s still too slow.
I’m thinking it’s an IC problem. I also installed the cap replacement kit, which only seemed to fix the sound.
Any solutions out there?
Thanks.

 

Does adjusting the speed trimpot change the tape speed or not ?