Hi I just purchased a used WM-D6C and feel I may have been duped. It said it was it working order, and I guess it is if you use the term loosely. It plays tapes, but as soon as I plug in the power it starts vibrating before even pressing play. Is this likely related to the problem below?... - common problem with servo IC burnt (CX20084), causing the motor speed to be too high and/or motor running all the time, even when in STOP mode. Also, it doesn't work at all on battery. The middle connector on the battery pack is completely missing... is that normal? Another strange thing is that it has the 'Amorphous Head' marking on the case, yet the head has the number '35712' written on it, which I thought was the permalloy head. How is that possible? The serial number says F10053. Also, if I put the volume up to about 5 and play without a tape, there's a considerable amount of noise. Is that also normal? Appreciate any advice. Thank you!
Hello and welcome to Stereo2go. Unfortunately, the fact that it's vibrating before pressing "Play" indicates that the CX20084 is damaged. The middle connector is used on the rechargeable battery pack (BP-23) but it is missing on normal battery packs, which take 4 x AA batteries. You mentioned that it started vibrating as soon as you plugged in the power. What type of power supply were you using? Switch mode power supplies (most of the plugtop ones sold in the last 20 years are switch mode), power supplies with the barrel plug wired with the centre pin positive and supplies delivering over 6V will all destroy a CX20084. As the CX20084 is connected directly to the incoming power supply, the damage will take place before pressing "Play" or any transport controls. Please see my post regarding the problems with the CX20084 and its use in walkmans, particularly the D6C: Sony WM-D6C and DD Series Walkmans - WARNING! Read this before plugging in any DC adaptor! I'm not sure about what is causing the noise but this could be due to a failing capacitor. Capacitor problems seem to be more common on the later, mostly surface mount, D6Cs.
Thank you for the reply. It came with a genuine Sony adapter AC-129, which looks pretty old so I'm hoping it's of the linear type. I heard the CX20084 is almost impossible to get hold of now aside from fakes. If I could get it working on battery power I could live with that. I've ordered some rechargable batteries as per the advice in your thread (many thanks for that; very comprehensive). So having the volume at 5 should not have a noticeable amount of noise from the headphone jack on a properly working unit? I admit it's been a long time since I've listened to a cassette deck, so it could just be a normal amount of noise. With Dolby-C it seems to mostly go away. Also, don't you think it's a bit weird about the head having 35712 yet the case still says 'Amorphous'? Could I have ended up with some kind of franken-walkman?
Even if your power supply is a linear type, sometimes the regulation on them isn't accurate as can be seen in the photos in my posting on the problems with power adaptors and CX20084 chips. I can't really comment on the noise without hearing it. If you are used to digital players then you may notice some noise on a walkman from the motor drive system leaking onto the audio circuitry. Regarding the head, according to the D6C write up on Walkman Central, some D6Cs fitted with the permalloy head still had the "Amorphous Head" sticker fitter. It cannot be taken as a reliable guide as to which type of head is fitted. https://walkmancentral.com/products/wm-d6c Here is some more information on head types on D6Cs: WM-D6C head difference
Thanks again for the reply. I have a digital multimeter arriving today, so I'll check the output of the Sony adapter, thank you. I recorded the output at volume level 5. On hearing the recording played back it doesn't sound quite as bad as it did through the headphones, lol. This is Normal, Dolby off. I've attached the file (it has extension MP3, but it's actually M4A). I guess it's ok? I'm not super concerned about the head I guess. I wanted this unit because I supply the sound for the old folk's karaoke here in Japan and sometimes they bring tapes. The servo IC is a bit more of a problem though. I understand you conduct repairs and also have a mod to help protect the IC after replacing. Would it be ok to PM you for a quote? Thanks. Oh, another quick question, sorry. If I got the battery working would the vibration when not being used still be an issue? Do the battery power and DC power both route through the same IC in the same so it would still be a problem? Update: I received the multi-meter. The Sony adapter is delivering about 6.8v; alkaline batteries about 6.5v; the rechargables about 5.25v. I'll steer clear of using the adapter, but the fact the vibration started the second I plugged it into the unit I'm guessing the IC was fried before I received the unit. The battery issue was an easy fix. The pins just needed bending out a little more to make better contact. Unfortunately the motor still spins, but less aggresively.
It's interesting to hear that the adaptor was delivering 6.8V. This seems to happen quite a lot with these old adaptors. I would recommend using rechargeable batteries only, which are more gentle on the CX20084 due to the lower voltage. I have listened to your audio sample and it sounds normal. There is a click at 1 second, where you switch the walkman on. After the click, there is about 1 second of silence. This is the time delay between switch on and the mute circuit unmuting. At around 2 seconds we can hear the leader tape passing the head. There is a quiet hiss and the 1.08kHz tone from the FG coil, which provides the feedback signal from the capstan to the motor controller. You need to turn the volume up quite high to hear these. At 7 seconds, the hiss becomes louder as the magnetic tape starts to pass the heads. The amount of hiss suggests the tape is recorded without Dolby. At 16 seconds the music starts. It seems to be playing at the correct speed and with decent wow and flutter which surprised me considering the possible problem with the CX20084 chip. The problem with the motor running when it shouldn't could be a problem with the circuit around pin 7 of the CX20084, which acts as a "Run / Stop" switch and is used to stop the motor in FF and REW when the end of the tape is reached. If pin 7 is high, the motor runs. If it is low then the motor stops. I have come across a case where there was an internal short within the chip and pin 7 was being pulled high from within the chip. Another possibility to check is the motor drive transistor Q601. Please feel free to PM me.
I made some measurements. Hopefully I did it correctly. With play unpressed, I seem to have 4.4v on pin 15, and 0.01v on pin 7 (goes up when play is pressed), 1.64v on pin 5, 5.13v on pin 8, and 0v on pin 16. On Q601 I have 4.45v, 5.2v, 5.2v respectively (left to right with the IC on the right hand side). Shouldn't one of these be 2.35v? Does that mean this component is bad? Or should I not have 4.4v on pin 15 of the IC to start with if it's not in play mode? I also tested in diode mode from the base to the emitter and also to the collector; both were 690 (mV?). Incidentally, my unit doesn't auto stop at the end on REW or FF. It does on PLAY though.
Hi, The auto stop feature on WM-D6 and WM-D6C models is only activated when in Play and Record mode. I was intrigued by your SN. I am used to 5 digit and 6 digit SN's used for all WM-D6C units built in what most agree were 3 distinct major revisions throughout the production life cycle. A serial # beginning with an Alpha character I have not seen. The heads and circuit boards vary with the revisions. Generally the early 5 digit SN units had the V shaped amorphous head and black text on white Dolby label on the rear. These are the rarest units. Rev 2 had the amorphous head but parabolic in shape and had the "35711" label on its upper surface. These 6 digit SN units had the brown PCB with many through the hole components used in place of the later SMD circuit board units with permalloy head. What none of us ever discover is when Sony changed the major revisions by serial number with precise ranges. You'd think that would be discoverable before it's lost forever!. I believe the later units in Revision 3, those with SN # over 500,000 had permalloy heads even if the body of the unit stated "Amorphous Head". You'd imagine the cases were bulk manufactured separately and were used regardless of what budget measures were implemented by the factory to contain costs. The engineering division would have been keen to use all inventory as digital was just around the corner.
There are two auto stop systems in the D6 and D6C. The mechanical system, which @Silverera is describing is only activated on Play and Record. There is an electrical "Auto off" system which stops the motor when the end of the tape is reached in FF and REW. This works by detecting rotation on the supply side reel. The D6C uses and optical sensor and the D6 uses a magnetic sensor. In the D6C, the Auto off circuit pulls pin 7 on the CX20084 low when the rotation stops, which cuts the power supply to the motor. A simple way to test the Auto Off system is to put the walkman into FF without a cassette in it. The take up spool should rotate and then stop after a few seconds as there is no rotation on the supply spool and the Auto Off system will activate. @Ray Price I think the most likely cause of your problem is a faulty CX20084 chip, however I would try changing the Q601 motor drive transistor first. There is a possibility that Q601 could be the problem and it is relatively easy to find a replacement. A point to note regarding the revisions of the D6C. As far as I know, Sony changed the Dolby label from Silver background with black writing to Black background with white lettering in 1988. They changed the head type from the "pointed" V shaped amorphous head to the flatter profile type before then so there are quite a few D6Cs with a flat head profile and silver Dolby stickers. If you are looking at a D6C on Ebay, don't assume that it will have the V shaped head if it has a silver Dolby sticker. I have attached the front sheet of the D6C Service Manual supplement which gives the serial numbers for the introduction of the SMD main board in various regions of the world. Rather surprisingly for such a major revision, the supplement doesn't appear to have a date on it. The last major revision of the D6C took place in June 2001. The motor servo circuit was changed to use the older CX069A chip, which had been used on the TC-D5 recorders in the late 1970s, instead of the CX20084. I suspect that this was due to a high failure rate, either in production test or during the warranty period, of CX20084 chips. The CX069A D6Cs are very rare as they were only produced for around a year before Sony stopped producing the D6C in 2002. I have only ever seen one of these. The manual supplement doesn't give a serial number when the change took place but serial number of the one I worked on was a six figure number starting with "518".
Thank you again for the reply. So you think the Q601 could still be faulty even though there's a voltage difference across both terminals from base? I'll try that first. Looks like it could be replaced using this... https://www.datasheets360.com/pdf/-5746879755448305012 I'll try that first, and continue trying to track down a CX20084 in the meantime. Thanks!
Hi, So the Q601 replacement transistor finally arrived (from China). I've never soldered components this small before, so it was a little challenging. I had to add MORE solder to get the old one off the board, and then the first replacement I tried to put on went flying out of the tweezers into the unknown . Anyway, with a lot of flux (and a new transistor) I finally got the new one soldered on. Unfortunately the original problem still persists. The good news is I haven't messed it up anymore. So I guess based on this it must be the CX20084 at fault. I might try and secure one over the next couple of months and if I manage to get one I'll PM you when I'm in England next and maybe I can engage you to replace it for me. I think based on this experience it might be a bit out of my league. Thanks
I find it amazing and amazingly strange that 17 years after the market introduction, Sony decided to revise the servo circuit. I can only assume that most units were sold in the 80s, so what was the real win here? For the 1%-5% of the buyers that bought the D6C after 2001, did the failure rate matter to Sony? We’re they going to go bankrupt for warranty claims on the final sales of this almost end of life unit? Or was it planned obsolescence of the CX20084?
Ray, please send me a PM next time you are coming to the UK and, hopefully, we can get it sorted out. Emiel, I guess this is a question which only Sony can answer. They clearly didn't plan to discontinue the D6C in 2001 but if they were getting a high rate of warranty returns, due to the widespread use of switch mode power supplies, they would have wanted to address the problem and protect their reputation for manufacturing reliable products.
