Hello! I recently acquired my dream Walkman, the DC2. It had an original problem of continuous playback when batteries were installed. I did some measuring and the CX20084 IC was the obvious culprit and after changing it from my working DD3 the continuous playback problem was solved but I was faced with another problem; the playback / ff / rew worked but only for around 8 to 10 seconds and then it shut off. The mechanical auto stop didn't go off, only the motor stopped and power led went dim. The issue is not mechanical as the motor draws around 96mA of current when playing without a cassette. Everything is cleaned thoroughly and lubricated, I have a new center gear and capstan ring installed. I've measured the FG coil and it's 730 Ω I've been following the schematic diagram and measuring caps and parts. So far I've changed the Q601 transistor, C303 cap and C608 and C612 resistors. After changing those, the playback stopping issue resolved but the motor is still running at 5170Hz and with 2.58V current. I've been measuring the voltages from different pins from CX20084 and tried to make sense of it all but it's probably just a busted cap or something. Before de-soldering everything and possibly ruining the whole thing, maybe someone could offer some insight of what might be wrong. Any help would be highly appreciated. Thank you!
Have you tried desoldering the PLL bridge ? Also that PLL adjustment trimpot seems to be with the cursor in a position where it's not touching the carbon trace at all. Check and adjust that accordingly, it must have 3090Hz with bridge disconnected.
Hi, Valentin! Yes, the PLL bridge is de-soldered. I've tried adjusting the trimpot but it only does like fine adjustment, nothing that explains the 2000Hz extra speed. I've measured the legs, it gives about 1k->22kΩ when adjusting it from minimum to maximum position.
Here's parts I've checked / replaced. CX20084 – replaced with another genuine CX20084 taken from a WM-DD3. (I also tried another one from D3 just to make sure) - No change Q601 – replaced and also checked with diode-test. No change. C303 – replaced with 47 µF. This fixed the shutdown problem. C603 – original measured 10.9 nF instead of 15 nF; replaced with a 15 nF part from the DD3. No speed change. C604 – measured 108.3 nF; also substituted with another 100 nF capacitor. No change. C608 – replaced. C609 – substituted with a known-good 1 µF electrolytic. No change. C611 – original measured only 26.3 nF instead of 47 nF; replaced with a good 47 nF capacitor. No change. C612 – replaced. Components measured and found OK C601: 8.7 nF (nominal 10 nF) C605: 1.8 nF C606: 10.28 nF C607: 10~ µF C610: 29.5 nF (nominal 30 nF) C613: approximately 33–35 nF R601: 210 kΩ out of circuit (nominal 220 kΩ) R602: 2.4 kΩ R603: 69.3 kΩ (nominal 68 kΩ) R604: 62 kΩ R606: 150 kΩ R607: 3.3 kΩ R608: approximately 9.9 kΩ R609: 96.4 kΩ (nominal 100 kΩ) R616: 45.7 kΩ (nominal 47 kΩ)
Have you check the FG signal at pin 3 ? Do you have a sawtooth waveform at pin 4 ? What about the reference voltage at pin 5 ?
I have not check the sawtooth waveform! This is where things start to go above my paygrade All I have is a couple of multimeters and I've tried checking the signal and voltages from the pins but I can't say I could make any sense of them. This is what I got from pin 3,4,5. Measured when playing. Pin 3 ≈ 1.185 V Pin 4 ≈ 0.87 V Pin 5 ≈ 1.55 V
After this it got me thinking that maybe the coil is in fact defective. I tried changing the the coil from a DD3 which has been proved to be working. The speed dropped to 4800-4900Hz And I got and bought myself a cheap oscilloscope as well. I measured the pins 3-5 Pin 3 Pin 4 Pin 5
DC voltages are close enough to not suspect a problem. Pin 4 may be ok, although unclear what those glitches I see are. On pin 3 (output of FG amp) you should have a clean sinewave which you don't. Make sure the coupling on the oscilloscope is set to AC if it does have such a mode.
I rechecked pin 3 with the meter set to AC. The waveform is still clearly distorted and definitely not a clean sinewave. https://i.imgur.com/yiMl65N.mp4
Make sure the trigger is set to EDGE mode and HOLDOFF is set to off/0. I see HOLDOFF on the screen in your previous pictures. To me it seems the scope isn't set properly because there are some dead spots in the acquisition, don't think this is how the waveform actually looks like.
I repeated the measurement with proper edge triggering and auto mode off. Still looks bad. I went down the line and also repeated the measurements at pin 1 and at the C602/FG input node using AC coupling, NORM mode and edge triggering. Both waveforms lock properly and the distortion is still present before the pin 3 FG amplifier output. So it doesn't seem to be an AUTO-trigger/acquisition artifact. C602 Pin1
I also measured directly from the FG coil solder pad on the PCB. I get the same strange distorted waveform that can be seen down the path towards pin 1. However, if I press hold at just the right moment, I can capture a clean sine wave. So the FG coil is clearly capable of producing a clean signal, but something seems to be interfering with or modulating it. https://youtube.com/shorts/nBUTAHQE9LU?is=QveTPhjc1aDjSgv3
Problem solved! I had the other FG coil wire soldered to the wrong pad. There’s three pads next to each other and even though the PCB clearly has the two FG Coil pads marked I somehow got it wrong well.. if you look at the mounting diagram like a dumb dumb and not the schematic diagram, this is what you get. Sheeeesh! Here’s wave from pin 3 after putting the wires correctly
The saga continues! Now that the speed issue has been resolved, I replaced all the caps on the audio board, and the DC2 sounds amazing! Well.. it will sound amazing but I'm having trouble getting the wow & flutter down. The main issue seems to be the motor spindle slipping against the capstan ring. There is also a slight vibration coming from the motor when the unit is running in play without a cassette. I've searched through the forum and tried pretty much everything I could find regarding this issue, but I'm starting to run out of ideas as to what I should check next. Here's what I've done so far: Disassembled the mechanism, twice, making sure every shaft and gear was properly cleaned and lubricated (IPA + ISOFLEX PDP 65). I'm 100% sure the problem isn't there. Everything runs very quietly and smoothly, apart from the slight vibration coming from the motor. Measured 96–98 mA in play / rew / ff without a cassette. The motor itself draws 12 mA at 1.5 V when I measured it separately. Replaced the pinch roller to a fresh one and made sure it makes even contact with the capstan. Treated the capstan shaft with ferric chloride. Adjusted the motor so that the spindle is perpendicular to the flywheel axle. Adjusted the motor bracket so that the base of the spindle is approximately in line with the outer edge of the flywheel. I also bent the bracket down a bit so that the spindle would make better contact to the capstan ring. Sanded the motor spindle with 1000 grit sandpaper, and also tried 800 and 2500 grit. I even tried treating the spindle with ferric chloride, but none of these approaches seemed noticeably better than the others. At the moment, the spindle is finished with 2500 grit. I also tried lightly sanding the capstan ring itself. I mounted the flywheel in a cordless drill and carefully touched the rubber surface with 1000-grit sandpaper while it was rotating. That didn't help either, so I flipped the ring over and I'm currently using the untouched surface. Tried changing the capstan ring / FG coil / capstan wheel. After all of these I figured the slipping was caused by insufficient motor spring tension, so I shortened the spring by a few millimetres. I didn't want to permanently modify the original spring too much, so I also added a second spring from my donor DD3 This improved the grip somewhat, but didn't solve the problem completely. Adding too much spring tension also starts to make the W&F worse. If I leave the thrust adjustment screw at the position where I measured approximately 98 mA and run it with a tape, the motor spindle slips like crazy. I have to tighten the thrust screw by roughly half to three-quarters of a turn before the spindle gets enough grip. I can get the W&F to around 0.12–0.15%. If I loosen the thrust screw from there, the spindle starts slipping and it's all downhill from there. It sounds OK as it is, but I can clearly hear the wow & flutter. I'd be happy if I could get it down to 0.07–0.08%. Does anyone have any ideas about what I might be missing? I'm wondering if the slight motor vibration and the spindle slipping could be related. Maybe the motor bearing has come to the end of it's life? Oh yeah, I did add a drop of oil in there as well. The vibration from the motor is amplified because the phone is touching the frame it’s not actually THAT loud
First of all, the flywheel thrust play I wouldn't adjust by measuing the current consumption because that tells nothing about the actual mechanical play. Rather, remove the motor and adjust it so you have 0.05-0.1mm of play (can be done by hand, with a piece of paper of feeler gauge) and lock the screw. Essentially you want to have a tiny bit of play, but nothing excessive. If you adjust by current consumption, lower consumption also means more play (and less grip) which you don't want. Another thing is the capstan ring itself. Is it the FixYourAudio one (a bit thicker than original, which is good in this case) or another one ? As for W&F itself, make sure the motor position is adjusted so it's perpendicular to the flywheel. This needs adjustment with capstan rings different than original. But it's also to be kept in mind the motor itself can cause high W&F on DDs, so there is no guarantee you will be able to obtain 0.08% with current motor.
