Does anyone know what these 4 pins control on the Sony WM-GX655?

When you place the 2 boards on top of each other the pressure of the spring loaded pins on the pads creates a conductive path for the 2 boards to communicate. Whether this is only to supply power or more likely some sort of digital SPI like protocol communicating across a 2 way data bus.

If anyone has more on this it would be greatly appreciated. I mostly wanted to know as mine were partly corroded and parts of pads are missing but it still all seems to work.

Im guessing the lower board closest to the tape mech controls the tape side of the operation and the top board (pictured at bottom in photo) controls the radio and possibly recording functionality. The radio Im pressure certain is on this board as it has a ferrite antenna installed on it.

 

Can't you trace where they go on the board?
From their position my guess would be either the battery, or the motor.
Did you notice all the other connections between the boards, which I have circled in orange. Those will be all the connections associated with the controls and display (assuming there is one). I have seen a similar connector on other Sony Walkmans, with a screw next to it the hold the connections tight. The annoyance is that you can't check the mechanism without reassembling the boards

 

Well done. Yes those finner pins look like the main means of communication while the 4 large pins would be for higher current applications

True, I also cannot find a service manual for this model

 

The WM-FX655 is the same model minus recording...see https://walkman.land/sony/wm-fx655

 

Looking at the board, those traces can't be for the motor as they're too thin and also motor drive IC (IC601) is on the bottom board.
It can be seen on the PCB diagram the motor is connected to the bottom PCB.

Those 4 pins are in the area where the tape in, normal/metal EQ, REC protect switches would be, so it makes most sense that's what it is.
Pin 28 of the main interconnect is labeled ATS SW (automatic tape select, 120/70us EQ), which would make sense to go to the analog board.
On the schematic/PCB diagram that connection doesn't seem to be marked separately.

As for the 2 boards:
- lower board is the analog board: motor servo (IC601), preamp, Dolby, headphone amp, rec amp (all these functions are done by the big Toshiba IC), bias oscillator (circuit can be seen around transformer marked 744 X);
- top board is logic control board + tuner;

Since there is only one microcontroller (on the logic board) there is no digital serial communication (SPI/I2C) between the 2 boards, but just control signals and analog signals (radio audio, FM annena from the jack).

 

Thanks Valentin. I always learn a lot from you! This is very interesting. I currently have this walkman working but there is noticable w&f and playback speed inconsistantcy. Its not as simple to connect to PC as it has propietry plug and Ive not rigged up some wires to find GND, LEFT, RIGHT signal to connect to either oscilloscope or the PC input for calibration. For now I'll leave it as is though.

I spent all morning today trying to get my Sony WM-507 to playback tapes for me but currently cannot get the motor to spin. I opened a thread here. If you have any sugguestions I could try, I would be very appreciative

 

Do you have a WFGUI screenshot of the W&F on both side to make an idea ?

 

Appologies, in the last post I said it had a propietry plug but this one also has normal audio jack. Sorry I forgot.

W&F Metre: The FW playback inparticular doesnt look good.

 

Something is likely wrong at the FWD pinch roller/capstan interface.
Speed is very slow at 1975Hz (assuming the reading is correct), something should be obvious: oil on the capstan/roller.
If takeup torque is low, it may also be that roller doesn't press against capstan enough.

 

I spent some time on this this morning and if anything I seem to have made it worse. Now both FWD and REV playback have ±150hz or so pitch variation when playing. I dont mean between RWD and REV but just in their isolated playback
What I done:
- Removed FWD capstan and cleaned bushings and lubricated with watch oil, then cleaned non bushing parts. Note: even before I did this the rubber cap on top of the capstan was essentric to make it appear like there is play. However I think its only because rubber cap is deformed a little. I cannot feel or see any play on the actual capstan.
- sprayed speed pot with wd40 contact cleaner and worked it back and forth for a bit
- inspected clutch gear and looks ok
- I dont feel any play in any of the pullys connected to belt

I tried to also film the capstan on the FWD side: Video

Its possible the pinch rollers are too worn down but they are spinning

 

Can't see anything obvious in the video. Also, given the severity of the problem, don't think the cause is something subtle like lubrication or a roller that's a little bit worn.
At first glance, don't see how lubricating the capstan bearings could have made the problem worse (assume any trace of oil on capstan and rollers was cleaned), unless something else happened at the same time.

Does the motor run smoothly ? Can you hear any pitch change in the motor whining sound ?
Another thing I would check is roller pressure. Try to put more pressure from back of the roller, see if you get any change in behavior.

The cap on the capstan bearing serves 2 purposes (of which none influences W&F): aesthetic and so tape doesn't catch in rough edges when cassette is inserted.

 

Yep as far as i can tell runs smooth no lateral play. Cant hear any pitch variation on motor or whining

Stranging, after work tonight I tried the calibration tape again with the software and I got new results:
Forward: 0.19% - 0.26%
Reverse: 0.22% - 0.34%

It seems to be much better than it was by sitting overnight. I have not cleaned and lubricated the reverse capstan bushing yet by the way. I guess thats the next thing to do?

 

These last W&F figures don't look bad, especially on FWD. Variation looks a bit high, would prefer those values to be more steady.
Are those max values are just occasional peaks or figure varies constantly ? How about those +/-150Hz speed jumps ?

Would lubricate the reverse capstan bearing too, yes.

 

It varies constantly but slowly like every half second it might change 0.01%.
Those +/-150hz jumps are gone thank god

Also after cleaning and lubricating rev capstan it seems to be alot better. Fwd and rev are both about 0.22% - 0.26%. I've calibrated speed and sounds pretty good. Only the first few seconds of playing tape sound a little rough but as you mentioned in other post its to be expected as the player to calibrates to a steady state.

Thanks mate. I'm dredding changing capacitors on the wm-507

 

Hi Valentin. I tested this walkman again today and the forward playback is working well, but the reverse is now struggling to pull the tape. It trys to pull the tape and then stops due to failure. I have tried this with several tapes but same result.
I've tried cleaning the capstan and pinch roller but still will not pull tapes in reverse playback
I tried reverse playback without tape inserted and the pinch roller spins nicely.
I have no idea whats going on all of a sudden. Any suggestions on how to fix?

Edit: I think this was due to slippage on the capstan, the lack of friction was causing tape to not be pulled. I cleaned very thoroughly with IPA and seems to be fixed

Edit 2: It seems to be happening again. Cleaning it with IPA worked for a while now its happening again. I have a feeling I may have put too much watch oil in but I have cleaned it many times and still no luck. What do you recommend? should i take capstan out again and clean it all with IPA then only put a little bit of watch oil on bushings this time? Or do you think it could be something else causing it to happen? When I put extra pressure on pinch roller it does spin a little faster but it still spins obsurdly slow before comming to a halt

 

There are a couple of possibilities (generally speaking):
- there is not enough traction at the capstan/roller;
This can be caused by oil contamination, pinch roller pressure too low, polished capstan.
Since these EXs have micro-grain capstans, last one is excluded. So is the first, given you cleaned already.
- there is too much resistance when pulling the tape;
This can be cause by other pinch roller being (partially) engaged at the same time (creating drag) or there is way too much backtension (this can be checked by hand).

Fact it happened suddenly suggests either tape contamination or pinch roller pressure problem. This may be related to the W&F problems you were having previously.
Roller spinning without a cassette doesn't tell much, try to put a finger on it (clean it after) and see if it has any resistance or you can stop it just by touching.

Is it only the leader it can't get past ? Or it doesn't have tractiuon anywhere ?

 

It not only the lader but seems to be from any position of the casssette on any side and of any tape even with ones im 100% certain shouldnt be contaminated

Its a reall strange problem.
- With no tape inserted: I tested the take up and supply side wheels on the walkman by entering the forward playback and reverse playback mode respectivly (Im pretty sure I got that right) and putting some finger pressure on the spindles untill they start to halt (slip has occurred at the clutch). The stopping torque for each spindle was simmilar so I suspect its not a clutch issue.
- With no tape inserted: I tested finger pressure to stop pinch roller from spinning in forward and reverse playback modes and to me the forward roller seems like a bit more force is required to stop the pinch roller from spinning. Maybe 30-40% more force required to bring roller to halt
- With an isolated tape removed from player, I've tested a the takeup and supply wheels with finger rotation in their correct direction to wind onto the wheel and both feel simmilar. Nothing excessive
- When playing in reverse playback with tape inserted: The pinch roller for the forward playback is fully engaged and I see no interference on the tape path. Edit: I've also noticed the tape does move and get pulled over head as it should (but at a much lower speed the forward playback) if the supply reel has very little tape on it and the majority of the tape is on the take up reel

What would you do next? I wouldnt mind swapping the pinch rollers but im having some difficulty removing the plastic frame. If I keep trying I'll eventually get it

 

Looks like it's a roller pressure related problem. Either there is not enough pressure or the roller surface is glazed and doesn't have enough grip.
Changing the rollers to see if the problem moves with the roller would seem like a logical next step.

 

I inspected both rollers and the reverse only looks slightly more glazed. I swapped the 2 pinch rollers around (without removing frame) to see if it would transfer the problem but it seems to have made it come good on forward and reverse now. I did notice a little piece of fluf on the pinch roller spring area but didnt think much of it. Im not sure if its a glazed roller problem or fact that i changed rollers has eliviated some connection. I think the later as it seems ok now. I'll keep testing it to be certain its all good

Edit: It came good for a minute or 2, now reverse playback is going ultra slow but at least pulling the tape until it completely stops. If i tilt the player so that the side of playback head that reads the tape points up directly perpendicular from the ground the playback comes to a halt almost instantly. It seems to me like the pinch roller may not be the problem. Interestingly too is that now the reverse playback roller (the one i transfered to the reverse capstan) is now 30% or so harder to stop spinning. this is confusing me. Do i need to re oil the capstan bushings?

 

@TP86
Reading all this don't you think it's time to swap the pinch rollers for new ones and then test W&F again?....you're going arond in circles without changing/replacing a very important part of playing cassette's, the pinch roller.
I've been seeing a lot of people struggling to get W&F right but never ever mention that they replaced the pinch rollers for new ones. They probably never been changed in the life of this walkman....
You can re oil, re lube all you want but if the pichroller is glazed it will never ever reach good W&F numbers.....just my thoughts