Pioneer LP-950 not Spinning

J

Jason Hirsch

New Member
I received an Automatic Quartz Direct Drive Pioneer LP-950 that's in great overall shape (apart from dust cover) from my dad a while back. The problem is that the motor won't start when I press play (platter easy to turn by hand.). I've cycled the table manually and have removed the bottom so that I could deoxit any contacts that I noticed in the start button mechanism, but neither of those helped. I've been unable to find a service manual for this turntable, and am afraid to do any more should I damage it further. Any thoughts on next possible steps or does anyone know where I could get a service manual for this model? Thanks!
 

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Thank you for the suggestion and link to the service manual. I'll certainly take a look at both, and let you know what I find.
 
Looks like there's continuity at the switch when tested. There is some slop with the start/stop mechanism, but I'm not sure how usual that is on these. I can't really see if the plunger gets pressed in or not and there doesn't appear to be any way to adjust switch position on this table. I've uploaded the service manual to vinyl engine but it might take a while to get posted.
 
I just lost the longer post I wrote, so here's a brief version.

(This is all done with the deck unplugged of course)

Check the fuse. Use a meter to confirm actual continuity rather than just eyeballing the filament. Also clean the fuse terminals and the contacts of the fuse holder.
Check the power cable for continuity.
Make sure that there are no transit screws that need to be removed (I think unlikely if you could move the platter by hand).

Back to the switches.
If you can't get to the plunger, detach the microswitch from the chassis (two screws, I assume). This should give you better access. There should be a port that you can use to spray cleaner inside the switch. You don't need to flood it. Push the plunger at least 20 times. Do the continuity check for all three terminals to see where you are getting continuity and non-continuity, and also what happens in each measurement position when you press in the plunger. If that all checks out, when you remount the switch, observe what happens when you press the start button - as far as you can see (and hear), does it mechanically operate the switch? Check the mechanism if you can, probably a spring, and whether it looks properly positioned and able to move (no hardened grease).

If you haven't done the speed switch, clean and test that as well.

Reading between the lines, you received the deck after a long period of non-use, and it hasn't worked at all since you have been in possession. If that is the case, that opens the range of possible faults quite a bit, which is why you need to start from the absolute most basic checks. It's very unlikely that I covered everything even for that. As I don't know this turntable at all and haven't seen the service manual, you'll probably have to hope that someone else can chip in on what to go for after that.
 
Thank you for the suggestions. The plunger on the microswitch is only visible once you remove the motor/board assembly. I did that and tested continuity of the switch. When I depress/release the plunger manually I get continuity readings between the AO/COMM, AC/COMM not necessarily in that order. I did spray some deoxit into the switch opening and cycle it a few times as well. Unfortunately, I'm not able to evaluate all of the start button mechanism with the motor, panel and switch removed. The button does feel sloppy when fully assembled (as compared to the tone arm lift and RPM buttons, so I'm still wondering if there is something in that linkage that's off. I don't see anything in the service manual calling out a fuse strangely enough, and I didn't see any fuses when I've had the unit apart. The service manual is too large to attach here, but let me see if I can PM it to you. Appreciate the help!
 
Thank you Tonoje for all of the suggestions. I'm still working my way through some of the items you PM'd me about and for anyone else interested here is the service manual for this turntable: https://drive.google.com/file/d/1CauH4HfVIcNnAbYhM30SxO39DYLrDw7w/view?usp=sharing

So far I've checked the following:
1. Microswitch: I've sprayed deoxit into the switch opening, and have cycled it many times. I've tested continuity and found that it is good with the plunger depressed and released.
2. It appears the start button does work as intended. When the plunger is pushed into the switch and the start button is pressed, the plunger gets released.
3. I've confirmed continuity of the power cord
4. I've gone around applying deoxit to other contacts as I find them
5. The Unit is a U.S. Military model and does have a voltage selector. It is set for 110-120V.
6. I have manually cycled the unit and that doesn't help things
7. The table doesn't spin when the unit is run in Manual mode and the tonearm is moved over the platter either
8. Transit screws and spacers were removed at the very beginning when attempting to use the turntable
9. It doesn't appear that this unit has a fuse from what I've seen in the service manual
10. Cleaned speed selector button with deoxit and cycled many times. Tested continuity across speed selector board and that seemed to look fine.

To be continued.
 
I hope someone else might have an idea where best to go next. As I understand it, manually moving the tonearm in toward the record operates the microswitch to start the platter, as pressing the play button would do. So if the switch is sound, something downstream of that must be causing the issue, which could even still be in the power supply section. Sounds like voltage check time, among other things. I don't know how or in what order to check everywhere between the switch and the motor, but I guess the main suspects are going to be electrolytic caps, bad solder joints, and ICs, particularly IC1 (motor driver) and maybe IC2 (speed control).
 
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Hmmm, not too many responses.

Er, how are you with a soldering iron? It can't hurt to replace the electrolytics in the power supply. That's only a few caps

Also you might try asking for advice over on Vinyl Engine. There's a subforum for Pioneer, but people are just as likely post their problems on the Turntables and Vinyl page, and you may get better visibility there. Your call, though.
 
Tonoje said:
Hmmm, not too many responses.

Er, how are you with a soldering iron? It can't hurt to replace the electrolytics in the power supply. That's only a few caps

Also you might try asking for advice over on Vinyl Engine. There's a subforum for Pioneer, but people are just as likely post their problems on the Turntables and Vinyl page, and you may get better visibility there. Your call, though.
Click to expand...

I don’t know this deck, and haven’t looked at the manual. So I’m a bit limited but….

If you do start to do any solder work, check to see if the voltages are correct on the PS prior to starting any cap replacement. The manual should provide the correct voltages in the schematics. I don’t think the power supply would power on the deck but not let the motor spin, even if caps were starting to go bad.

that said, I 100% agree start with the power supply. You want to make sure the voltages are correct, than move on to the next board.

my guess is it would be one of the ICs in the control board, or if you pull the motor there should be a board under it with a few small value caps, those caps could have drifted. Usually not a cap issue tho.

It’s a DD and quarts locked, I’d start testing any ICs you can find. :)
 
Sorry, I havent been on for a bit. So, I partially disassembled the turntable yesterday and using a multimeter checked a couple of easily accessible ICs. With one lead on Pin 1 and the other working around the other pins on the two ICs it appeared that there was a short in each of the tested ICs at one pin. Is it common for ICs to crap out on quartz lock direct drives? Also, while this is probably captured elsewhere, what is a good resource for replacement ICs? Debating if I want to attempt fixing this with my ham fists, or paying someone with a bit more soldering experience. To top things off now my SA-950 amp is acting up with a channel going out....
 
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