The DD tape transport does not have a clutch for FFW and REW, the motor is in direct connection with the reels; when the tape ends both reels stop spinning, the capstan also stop spinning and the motor starts slipping on the capstan rubber ring. I've read somewhere that the circuitry detects the increase of current absorption by the motor and then cuts the power; but I think that power is indeed cut if the coil does not send any signal. You can try this test: push the motor downward so that it does not make contacts with the flywheel; engage playback and you will see the motor spinning at full rev and then after few seconds power is cut.
I see, have now a few more questions and will force myself NOT to ask them, I find this extremely interesting and otherwise it will never stop! Thanks again enryfox, your understandable description of deep technical matters is invaluable especially with your specific knowledge in regards to our hobby. I think your first post in this thread nailed down and the title of the RevDocs topic.
I think we should distinguish between the Disc Drive mechanism here and the servo circuitry that is used for controlling the speed. The Disc Drive has actually proven to be very much a very lively end.... The most sought after Walkmans today are all DD walkmans because they still sound better. Regardless weather a Quartz oscillator was uses as a reference or not. But this drive was too bulky and too costly to continue with for the newest/thinnest walkmans. The newer, flatter, multi-pole motors required different servo circuitry. A funny detail: they kept the IC number for the drive servo in the electrical circuit diagrams the same throught (as far as I have checked service docs from '80 to '93): IC601
The disc drive mechanism is a great piece technology and back then it was truly amazing. It was a dead end because it was bulky, power hungry and an auto-reverse with DD (DD9) was way too expensive. The quartz lock is an impressive feature to print on the box, but it actually address a problem no one had (absolute speed is not that relevant in a playback only device). As for the audio quality, Hugo has reviewed several other later walkman's and I think that some of them have a better audio path than the "average" DD (DD, DDII, DDIII, DD30, DD33), but they all fail the W&F test which is the selling point of the DD. I would have really liked to see a new DD after the DD33 with all the advancement in electronics of the 90's, but it never appeared, W&F of the ordinary belt driven walkman's was deemed good enough.
Somehow I doubt that ! But even then it doesn't matter there is always the next question. Thanks anyway. Actually I was thinking about that you read that the circuitry detects the increase of current absorption by the motor and then cuts the power.Is there a possibility that this is also applied along with feedback from the FG coil ,something like AND - OR situation ? If there is such a function would probably be somewhere in the servo IC ,the datasheet of the the IC should mention it. I had a rough idea, for the test you proposed, if altered a bit and somehow manually keep in motion the capstan so there is feedback from the coil and simultaneously hold the axle of the motor to almost stop, to increase the current absorption ,that will reveal ,if the motor stops, that there is this function ....or that we tortured a poor DD to death. Too academic all this but helpful practically when you try to understand the nature of a malfunction during a repair. I have some questions for the future for another mystery in the walkman universe :The Sony WM7.
The servo IC's for the DD line are Sony proprietary and there is no data sheet available. I only have the block schematics that is shown in the service manuals, but that can just give a general idea of who's doing what. In all cases, the signal to shut down the motor come from the Servo IC and there is no clear indication on what is triggering the shut-down. I checked the service manuals of four DD's (DD, DDIII DD30 and DD33) and even though the principle is always the same, the circuitry and the IC's are slightly different; it is notable that the PLL IC's in the quartzed models requires a DC/DC converter to step up the voltage to ~6.5V; moreover, even if it is marked as PLL it looks like as if it is only used to generate the reference signal for the servo IC. The quartz oscillator has a resonance frequency roughly 28 kHz that is down scaled to 833 Hz (the five flip/flop in the PLL IC does a 32x downscaling of the frequency) and fed to the servo IC as a reference. I guess the capstan is rotating much slower than 833 Hz so there must be another frequency divider somewhere in the servo IC.
Didn't find the datasheet either , but found the pin functions. CX20084 pin functions are as follows: Pin main function 1 FG amplifier input (+) 2 FG amplifier input (-) 3 FG amplifier output 4 sawtooth time constant Setting 5 Power Output 6 PLL input 7 power switch 8 power supply Vcc 9 automatic cut off 10 double integral circuit time constant setting 11 sampling and holding circuit time constant setting 12 Buffer Output 13 Phase Compensation DC Amplifier Input (-) 14 phase compensation DC amplifier input (+) 15 phase compensation DC amplifier output 16 ground
I just think when the over heated flux capacitor redirects 7 volts through the dynamic coil induced vacumm thermos you are in danger of the 240 regulated back bunsen jet restricter getting carbonated by the single phase block dynamics of the forced coupler.
