PL-8 Unsteady quartz lock

[QSilver]

I thought I'd posted about this a while back but after a lot of searching I haven't found anything so here we go.

I bought this PL-8 a year or more ago and it wasn't working when I got it. I managed to get the SM from fellow AKer, Beej, so big thanks for that.

After doing some probing and testing the voltage rails, I followed the "troubleshooting" which led me to think that the drive IC, PA2008 might be faulty.

I bought a new one from Germany and fitted it but nothing changed - still dead. All the functions work but the motor doesn't turn react to anything.

After bashing my head on the desk looking at the troubleshooting and testing the board, the obvious suddenly dawned on me...

R10 wasn't there....

I did have some 2.2 Ohm resistors on hand so I put one in and.... LIFE!

But, the catch is that the rotation is unsteady. At the same point in one revolution, the motor applies the breaks slightly and then carries on.

I've tried the calibration procedure but the waveform is not stable enough to guarantee the 3/2 step in the waveform.

I also checked the frequency present at Pin 7 of the PA2007 IC and 33.3 gives me 55.5Hz and 45 gives me 75Hz as they should. However, when running on 33.3RPM at the section of the rotation where the motor "breaks", the frequency on Pin 7 drops to 10-25Hz.

At 45RPM there is still a slight problem but less obvious unless you're looking at the scope.

I have already replaced PA2007 with another PA2007 from another Pioneer turntable I own while trying to make this one work. Troubleshooting seems to be pointing at a problem with PD1003 or the quartz crystal. Or is there something else?

 

[Watthour]

Is the 23V supply correct? Ans steady?

 

[QSilver]

Measures 24VDC. Only a little bit of noise present when the motor is running which corresponds to the jerking or breaking.Besides that its steady.

 

[Watthour]

I apologize in advance for all the "dumb guy" questions, but I did not see the information posted earlier:

1. If you remove the platter to reduce the load on the servo, does is maintain speed?
2. Does the "Lock" LED illuminate?
3. Do the four electrolyitics in the output phase circuits (C18-C21) all test at approximately the same capacitance and ESR?
4. Do the waveforms from the PA2007 all look similar to those on the schematic?
5. It appears that the frequencies from the 2007 are correct, but if you are concerned about the crystal, did you measure for the 1.5KHz rate at Pin 15 on PD1003?

Waiting for information.

 

[QSilver]

1. If I remove the platter, the motor doesn't co-operate, its runs forward then backward but this is normal for these hall motors I think as I have a few of these later Hall motor TT's and they all require the weight of the platter to run properly. They require the momentum I think.

2. Lock LED does light up but when the motor "breaks" it goes out. You can hear a quiet clunk when this happens which corresponds to the motor braking.

3. I've replaced all the electrolytic capacitors on the board. The small ones around 1uF or less are now film and the larger 10uF capacitors connected to the coils are now low leakage nichicon KL.

4. The waveform from PA2007 for calibration, does look correct, however the flat spot that is supposed to be aligned to the bottom 2 sections of 5 sections on a scope, darts around in time to all the other problems mentioned - the braking, noise and the lock LED going out. The flat spot seems to creep up the waveform and then re appear at the bottom as if it's slightly out of sync. Adjusting the speed pots doesn't alter this behaviour, but alters the speed of the platter and moves the flat of the waveform for a moment before it continues to jump around.

5. I'll measure Pin 15 of PD1003 and check the frequency.

Hopefully that makes some sense - describing what the deck is doing can be a bit difficult as "quiet clunk" can mean different things to everyone. When I've set up my other decks in the past, the waveform on PA2007 is fairly steady once set, but the flat spot on this one just keeps jumping up and down - like it thinks there is sudden over speed but only once per rotation. Maybe it takes one rotation for it to compare its running speed with the quartz lock reference?

No worries about the "Dumb Guy" questions, better asked than assumed and I'm grateful for the help.

 

[Watthour]

Are we certain that the motor is solidly coupled to the platter, and that there is no play or loose connection? That might induce some weird feedback.

 

[EngineerNate]

Any visible cracking in the magnetic rubber strip around the perimeter of the motor rotor?

 

[QSilver]

Are we certain that the motor is solidly coupled to the platter, and that there is no play or loose connection? That might induce some weird feedback.

Fairly sure. I've had the motor out a few times now and I always securely screw it back down to the chassis. The Platter is a friction fit - conical machined shafts on the patter and motor spindle - it always needs a firm tug to remove it. I don't think there are any loose connections, I've tested connections between plugs and sockets and they all measure 0 ohms.

Any visible cracking in the magnetic rubber strip around the perimeter of the motor rotor?

Not that I noticed any when I last looked, but I'll take another look and see what I find. I was starting to wonder if there is an issue with the FG or if a Hall Sensor had moved slightly?

 

[Igor_SPb]

I was starting to wonder if there is an issue with the FG or if a Hall Sensor had moved slightly?

You can disconnect the motor, turn the platter by hand and see the FG signal stability with an oscilloscope.

 

[sam562]

Fairly sure. I've had the motor out a few times now and I always securely screw it back down to the chassis. The Platter is a friction fit - conical machined shafts on the patter and motor spindle - it always needs a firm tug to remove it. I don't think there are any loose connections, I've tested connections between plugs and sockets and they all measure 0 ohms.



Not that I noticed any when I last looked, but I'll take another look and see what I find. I was starting to wonder if there is an issue with the FG or if a Hall Sensor had moved slightly?

I'm curious, did you ever get this turntable up and running smoothly?

I recently noticed some possible errors in the PL8 service manual (downloaded from vinylengine) while I was working on my dead PL8

Mine would power up and show appropriate LED lights but wouldn't spin the platter.



Possible Errors:

On page 32, in the third step of the "Motor Dose not Turn" (sic) troubleshooting flowchart:

Is PLAY/STOP terminal less than 0.5 volts? <--- I think they probably meant to type 10.5 volts because that is the reading I get (measuring across the play/stop switch) when I finally got it working.

On the Motor PC Board:

Resistor 10 reads 2.8 ohms (measured in circuit) instead of 2.2 ohms. It's covered with woven heat shrink so I don't know if it's just an out of spec 2.2 or an an actual 2.8 ohm resistor. (possible design revision) (I wondered if this difference would make any difference for your symptom)

Resistor 5 is actually a 10k resistor instead of 16k (probably a design revision)

Resistor 2 is a 4.7M but mine was out of spec and reads 5.3M (measured in circuit)

The filter cap in the PL8 service manual only calls for a paltry 470uf/63v which is very strange considering the PL8's lesser brethren (PL5, PL7 etc) which are damn near identical all have 1000uf/50v filter caps installed -- but worse yet, mine only had a meager 330uf/63v installed! I can't imagine why they did this. There is plenty of space too.

Another minor service manual error is the instructions for adding silicone fluid to the lift pin: there is no "grooved section" on the pin but the location noted is correct. Also, I put a bit more than a bead of 100K silicone half way around the shaft. I add dabs on the other half as well. The reason why they don't want you go all the way around with a solid bead is because it creates a surprisingly strong pneumatic seal that prevents insertion of the pin due to the resistance.



I'm a novice tinkerer so in order to fix my dead PL8 the first thing I tried was reflowing all of the soldering joints, because they were all very lean on solder and I've had luck with this approach before...but unfortunately not this time.

The voltages in the above mentioned flowchart weren't matching my multimeter readings so this lead me to believe that PA2008 chip was likely the problem. I pulled that chip from a working PL5 motor that I had bought for another broken turntable but ended up not needing (reflowing fix worked that time) I switched the PA2008 IC out but no dice - the platter still was not spinning.

The next IC to change in the flowchart was PA2007 so I switched that one out as well and, viola, it spins!

I decided to up the filter cap to a 1000uf/50v and I replaced the three caps on the control board. I also cleaned and lubed the mechanism, cleaned the microswitch contacts.

It works great now.


--------Notes----------

Pioneer PL-8 Turntable (also sold as PL-470 in Japan)

WORKING TABLE ACTUAL VOLTAGE READINGS - POWER BUTTON ON, START/STOP NOT PRESSED :

VCC 24v

START/STOP Terminal 10.5v

IC TC4011BP, Pin 3: 0v (~.5mv) after diode: 0v


PA2008 PIN VOLTAGE:

1 7.5v
2 24.3v
3 1v
4 10.5v
5 0v (supposed to be 5.15v)*
6 2.6v
7 24.3v

8 7.8v
9 7.4v
10 7.8v
11 5.4v
12 4.8
13 16.9v
14 17.5v


PA2007 PIN VOLTAGE:

1 3.3v
2 3.2v
3 3.2v
4 5.4v
5 0.7v
6 0.7v
7 0.15v (supposed to be 1.2v)*
8 0v


9 10.5v
10 0.3v
11 2.7v (supposed to be 5.0v)*
12 0v
13 6.3v
14 6.3v
15 6.3v
16 0v

* - according to service manual