Dir Drv TT spinning at about 100 rpm

CavScout

Super Member
I bought a vintage Pioneer PL-4 Direct Drive Turntable for $30 in decent shape.

Upon testing it the platter began to turn backwards and then it went forwards EXTREMELY fast !

I took it apart and cleaned the speed select switch and also the pitch potentiometer (DeOxit) but it didn't change anything.

I downloaded the manual but I didn't find any useful info.

Do any of the experts on here have any idea what it could be ?
 
I'm no expert but offer advice. If you deox'd the pot & speed selector while rotating/selecting, I'd lean toward bad caps. It could also be a bad pot. Replacing is a fairly easy & straight forward process. Replace w/the same value. Desolder, remove, solder in New. Done.
 
They most certainly could. Go ahead and look at the schematic; an IC (PA 2007) controls the speed. A bad cap or one too far out of range will change the speed easily.
 
I did a recap of the lytics (~9 of them) of a similar PL-300, then another guy replaced the trimmers inside and fixed the rogue speed issue.
 
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Thanks.
Which board do need to replace the caps on ?
The small board with the pot on it or the larger board connected to the motor spindle?
 

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Both. Replace all the electrolytics (the black and blue and gray cylinders) they are all at least 40 years old. They're cheap and not even worth the trouble of testing.
 
You're not gonna nail it - it's a waste of time. Clean that pot with deoxit. It doesn't look like a pot that needs replacing. The variable resistors, however, those semi-open trimmers and old caps, do!
 
Yeah? Well it's probably a loose translation from Japanese offered in the link, but at least it's a description and it aimed to help by addressing a query. Feel free to enlighten us all, provide the correct description and link to a datasheet if you can. This way, your response would stay productive and educational.

Pardon. I'm not one to use a sentence when a word will do. A pulse transformer is a common component: https://www.digikey.com/products/en/transformers/pulse-transformers/166

I did not clean VR1 or VR2.
Would that be with deoxit ?

Yes, though there's an argument to just replace them as tnsilver mentioned. One or the other is in series with the pot as selected by the speed switch - the service manual explains how to adjust them.

Power supply voltages and ripple is the first thing to check, followed by the presence of the FG signal as mentioned by illini. I'm not a fan of shotgun parts replacement as a troubleshooting step, but if you don't have test gear you may not have a choice.
 
You're not going to find a data sheet; beside it being old, it was made for Pioneer (I believe it was proprietary), but I'm sure you knew that tnsilver. It's the speed controller and you can call the IC a clock or a pulse transformer w/no problems IMO. The caps help control the output speed and that will need to be addressed. I'd imagine the cost of the caps wouldn't be too expensive...less than $10 easily. None are of high value and there are not that many (board PWM-060). It's up to you if the cost & labor is too great to keep your TT alive.

Yes JP, checking output/input voltage will help and is a good t-shooting technique one should start with. I'm still saying, w/out t-shooting, the problem are the caps. It has output as described by his initial description. The reason for the slow speed are the caps. At least IMO.
 
It's unlikely the IC is bad. They're generally pretty tough. Much more likely is a bad cap/resistor/solder joint in some critical spot.

Where are you located? Someone may be local to you and willing to help troubleshoot. :)
 
The reason for the slow speed are the caps. At least IMO.
The OP's complaint was rogue speed (100 rpm?). :dunno:
That happened to me once with one of the cheapo Pio's (PL-300) someone left for me to "see what I can do" and never bothered to phone about it since. The feather weight platter was going so fast I was worried it'll go air borne and chop my neck. It only had 9 lytics on it, all cheap Nippon Chemi's and Rubycons from the 70's. I tested only the PS cap for ESR and it was way off any of my older charts. I didn't bother with testing the rest, most were low voltage low capacitance EC's so it was a five bucks worth of a complete recap. But that wasn't the end of it. I gave that abandoned TT to a forum member who was sold on the quartz lock drive and expressed interest in fixing it, as it was. He just replaced the two trimmers that probably developed dead spots, and that, plus the earlier recap, did the trick.
 
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