Pioneer PL-X9 motor speed control wobble

[Bushcat]

I'm starting to re-cap a Pioneer PL-X9 turntable, specifically the motor control board, because although everything tests out OK according to the service manual, the speed wavers slightly despite the quartz lock light remaining on. So, I've decided to re-cap that board since it's the cheapest next step...

Pioneer's passive component naming convention is clear to me. For example, CSZA R22M 35 is tantalum, radial leads, 0.22uF, 20%, 35V.

BUT there are two capacitors on the board which have actual Pioneer part numbers: PCL-042. I can tell they are 0.1uF, 16V but don't know why Pioneer would do this, unless the capacitors are special somehow. Any ideas?

There's a second oddity: CCDCH 330J 50 means ceramic disc, disc-type radial leads, thermal compensation with a thermal coefficient of 0 and tolerance of 60 PPM, 33 pF, 5%, 50V. So that's a generic passive component naming scheme, for an apparently special capacitor. I have no idea how to find a modern equivalent. Again, any ideas?

[stj]

Re: Pioneer PL-X9 motor speed control wobble

very stable accurate caps makes sense for such a circuit,
you will find ceramic and plastic film caps in 5% or even 2%

i wouldnt be surprised if the 33pF caps are connected to a crystal.
you probably wont find a .22uf tantalum, i would use a .22uf 63v plastic film cap

[Bushcat]

Re: Pioneer PL-X9 motor speed control wobble

The 33pF cap is indeed connected to the xtal. So this would be a Class 1. It seems CH is interchangeable with C0G and I've seen datasheets for Murata, Kyocera and TDK.

[redwire]

Re: Pioneer PL-X9 motor speed control wobble

Is it stable in variable-speed RC mode (not quartz)?
The 33pF parts are likely fine and not the problem I think. The electrolytic capacitors are old though, and I would replace them all.
Looking at the motor control board, 13 electrolytic caps to change. The values 0.22uF, 0.47uF or 1uF I would use film caps instead like Kemet R82 or Epcos/TDK B32529 or Panasonic ECQ 63V series.

Check the +18VDC power is stable from C20/IC12.

Service manual I found here: https://www.vinylengine.com/library/pioneer/pl-x9.shtml There is ARP-234 and ARP-382 version.
There is a special Pioneer Tuning Fork repair guide https://www.hifiengine.com/manual_li...ing-fork.shtml which can explain the circuit.

One person found the Pitch pot and wiring was bad, and cleaning the switches, and another person had a bad IC3 PD1003.

[Bushcat]

Re: Pioneer PL-X9 motor speed control wobble

Vinylengine doesn't accept registrations from Japan, but I do have the two service manuals: the original with the stunningly arcane adjustment steps, and the simplified one which requires the special setup record. Also the Tuning Fork guides nos 2-9, which have been helpful.

Reading the spec on IC3, it seems like the RC mode is actually disabled. I'll check the 18VDC.

Thanks for suggesting alternative caps. I used to be pretty OK at audio repairs decades ago, and have started to revisit my youth, buying the audio gear I couldn't afford then. The sheer range of capacitors now is kind of daunting, so I'll go for your suggestions :-)

TP1/TP2 are important enough to label clearly, and they're spaced on the PCB to take some kind of test connector, so I assume at the factory something could be plugged in there while the speeds are adjusted: there are only two VRs on the board.

A second turntable just arrived which I bought accidentally, so I now have two chances at a good machine. The second "junk" one may be the most valuable, because the cartridge came with a needle which seems to be in good condition.

[Bushcat]

Re: Pioneer PL-X9 motor speed control wobble

Update: 18V rail is fine. The second "junk" machine is largely functional and has a perfect needle. In particular, it keeps good speed. However, it can't count beyond 5 tracks, and messes up jumping between them: it won't skip beyond track 3. Anyway, I put its motor control board into the original machine, which now has rock steady speed. However, the "can't count beyond 3" problem has followed it to the original machine, which seems counter-intuitive. Work interrupts for several days, when I'll re-cap both PCBs and put the original board back. Examining both boards shows a couple of caps are skewed before soldering, presumably to clear stuff. Also, every capacitor is 7mm high, so I need to re-think a couple of the replacements since it looks like the PCB is, indeed mounted with only 9mm of headroom.

[Bushcat]

Re: Pioneer PL-X9 motor speed control wobble

I finally got all the replacement electrolytics to replace the existing ones. And... they're too tall. All the existing electrolytics are 7 mm tall, for every value from 0.47 uF 50V through 100 uF 10V. My replacements are 9-11 mm tall. The headroom above the board is 9 mm. So the replacements don't actually fit. For the life of me, I can't source 7mm tall electrolytics from brands I actually recognise. In general, could I use conductive polymer such as the Panasonic OS-CON?

[stj]

Re: Pioneer PL-X9 motor speed control wobble

you cant get polymer below 100uf afaik.
rubycon does some ranges of short caps
or can you put what you have on their side?

[Bushcat]

Re: Pioneer PL-X9 motor speed control wobble

I only seem to be able to get Rubycon PK series here, which start at 11 mm. I could lay a couple of the capacitors flat, but in general it's a tight fit in there in all directiones :-(

[redwire]

Re: Pioneer PL-X9 motor speed control wobble

Are you sure the height is that low for all of them? Or just a few?

[stj]

Re: Pioneer PL-X9 motor speed control wobble

i dont know your cap list,
but maybe you can use some tantalums - even smd on the back of the board!

[Bushcat]

Re: Pioneer PL-X9 motor speed control wobble

Are you sure the height is that low for all of them? Or just a few?

All of them. The board is upside down, underneath the turntable, inside the black plastic tray in that pic. It's actually slightly less in one corner, and the cap there is bent over. I'm not talking about the main PCB visible in that pic.

i dont know your cap list,
but maybe you can use some tantalums - even smd on the back of the board!

If tantalums are OK, then there is plenty of Tancap brand available, if that's a reputable company. I've just found some Toshin stuff, but it states it makes some components, and imports other components. I'm trying to stay with name brand Japanese caps if possible, partly for the aesthetic and partly because of quality concerns.

[stj]

Re: Pioneer PL-X9 motor speed control wobble

i dont know any asian tant makers, but nec or panasonic may make some.
in europe they are mostly made by kemet or AVX

[Bushcat]

Re: Pioneer PL-X9 motor speed control wobble

So, I replaced all the electrolytics with new electrolytics and some tantalums, reassembled it and it still functions (yay!) but with the same speed wobble (awww...). I tested each cap as I removed it, hoping to find a dud, but they all tested OK.

So I think I'll do the caps around the xtal oscillator next. These are 33pF and 50pF 5% items; I've not been able to locate Japanese replacements yet.

[stj]

Re: Pioneer PL-X9 motor speed control wobble

the caps on the crystal never fail, but crystals can drift.
BUT FIRST - are you sure it's not the motor? maybe a drop of teflon-loaded oil on the shaft would be good

[Bushcat]

Re: Pioneer PL-X9 motor speed control wobble

I could swap the rotor out from the second turntable. You're right, that needs testing. The design has the coils on the PCB. The rotating component is basically a flat disk with a large annular magnet. What is also the turntable spindle is hollow, and sits on a fixed shaft. The contact point is a teflon pad. It's all been cleaned and lubed. It spins reasonably freely. I do wonder if one of the coils is out, but it seems to test OK.

[redwire]

Re: Pioneer PL-X9 motor speed control wobble

Like I said, run the turntable in adjustable speed mode and see if the speed still wobbles. This makes it ignore the crystal and use an RC oscillator. I would say it's not the crystal or the loading caps, the frequency does not go up and down - any problems and a crystal osc just stops completely.

I think if the speed wobbles, the control loop is unstable which implies the tachogenerator "FG" has weak output. I would look at that. The motor could be it if the speed falls too low but this is not common.