Thank you so much for this thread. I finally picked up an absolute mint condition PC202 MkIII today. Almost the same model but with the Dolby-C circuit (which I heard is actually not the best on this model and isn't maybe worth the trouble trying to source over the Dolby-B only version). My motor hums really badly. Here's a sample: https://voca.ro/1ntlFmCclc5S The speed reports about 3082Hz on a 3000hz reference tape. The hum it's very audible, likely the caps are gone and it needs a proper cleaning and repair which I will attempt myself. So I am really appreciative that you've put so much effort into all these photos and explaining everything clearly. Thankfully this is not a "rare" model so there's quite a bit of information around about it. But it looks like it will be time to try my luck at micro-soldering and buy the capacitors I need. Unfortunately with the motor hum there's a lot of potential causes, most likely is the capacitors and increased power draw from the engine. I'll be opening up the device this week to figure it out and I'll post my findings here rather than make a new thread. That said, she's a beauty and came with all the acecssories including the case, bag and even the EU adapter which often goes for up to €50-80 on its own. I've never seen one in this good condition except for a few years ago when an eBayer was selling about a 100 or so of these BNIB and I missed my chance on one of those.
Dolby C indeed will not work well on this unit as-is. It will need calibration to work as intended, all PC202 and P202s I have serviced were off by a pretty significant margin. It's to be noted Dolby C is very sensitive to tape path misalignment and levels, unlike Dolby B which has more margin. That's why the P202 unit may seem better in regard to Dolby decoding despite both units are off. Then a properly recorded cassette tape is a must for Dolby C. This means a deck with external cal (both bias and rec sensitivity) or autocalibration. The PC model typically uses Nippon Chemicon capacitors (which are less prone to leaking), while the P model uses Nichicon ones (which always leak). Capacitor values are slightly different from the P unit. See picture attached for values. It's very important that caps are as small as possible. The output coupling capacitors (the 2 unmarked near the headphone jack) can be either 220uF or 330uF. Originally the PC uses 220uF (while P version uses 330uF), but 330uF will render lower output impedance at low frequencies, so these are to be preffered if available in this small footprint.
Has anyone actually got Dolby C to work well on these models? I cannot get rid of the pumping effect (that was also evident in Techmoans video) no matter adjustments of Dolby levels. I figure I have built up enough experience with Dolby C now with close to 400 Dolby C recorded tapes (well calibrated deck with proper Bias for each tape) that plays fine on my calibrated Walkmans (2xD6C, DC2, DD9 and 701C). However I bough PC202MIII and PC203 (which I believe is more or less identical) to use on the go. I cannot get a satisfactory result with Dolby C. Dolby B recordings sounds fine. Aging capacitors that makes it out of spec?
I got very good results with the PC202s I serviced, Dolby C decoding working exactly as it should. As already mentioned, capacitors aren't usually a problem on this unit. Besides none of the electrolytic ones have anything to do with Dolby NR decoding. So while replacing the capacitors is recommended, they're not the reason why Dolby C is not working as intended. So in such cases, there's something else causing Dolby mistracking. The 2 things I would looks into are: 1. Tape path alignment. Even slight misalignments will cause Dolby C to mistrack. A mirror cassette would be ideal to check this, but it can be checked by removing the buttons cover and observing if the tape is moving up or down near the pinch roller after pressing play. Problems causing this can be a capstan that doesn't sit perfectly straight, uneven wear on the capstan, pinch roller that sits at an angle, incorrect azimuth adjustment, head wear, etc. 2. Tape EQ switch. On these units, oxidation on switches and volume potentiometer is pretty bad, often requiring more than one cleaning for proper operation. If you are playing a TYPE I cassette and EQ is set to 70us (despite switch is set correctly) due to oxidation in the switch, Dolby C will mistrack. These problems will manifest on Dolby B as well, but it will be way less obvious since B has a lot more margin.
Thanks for posting the capacitor list Valentin! Do you know what voltage these are? I'm thinking of recapping pretty much everything with tantalum caps. Are they all 2.5V? Looking at buying them from here: https://eu.mouser.com/c/passive-components/capacitors/tantalum-capacitors/ I need the voltages in addition to the resistances. Would anyone also have a specific brand that you'd recommend?
Most of the capacitors operate at a voltage of 1.1V, so any rating of 2V or higher is just fine. Main concern here is the dimension not the voltage rating. There was a capacitor kit for these walkmans on ebay (which I would recommend), but seems it's no longer available. Given this, tantalums are a good option at least for the smaller capacitance ones (4.7uF, 22uF, 47uF). But to be noted through hole ones are needed, not SMD. The 220uF and 100uF are to be checked if they fit, but these are available as electrolytic in a footprint close to original one. For 220uF, TAP227K006CCS are the only reasonably priced THT tantalums, rest being more than 10euros/pcs, but even these seem to be too large at 14.5mm height, original being 5mm. As far as brand goes, any brand sold by these big electronic components distributors is fine.
I looked around a bit to try and source the caps but this ended up being one of two models I handed in to the local repair store. They have a whole bunch of caps for many different models and have fixed hundreds of Walkmans. I haven't had dealings with this store before but the guy at the desk was very confident they could fix this (and the Panasonic RQ-S90F) back to perfect sounding condition including any necessary soldering part replacements or capacitors etc. I'll get it and the Panasonic back with a full report so I can explain what was wrong. Haven't the time to fix these two myself.
