fini Posted August 11, 2011 Share Posted August 11, 2011 I've been trying to figure out how to repair the tonearm cueing/lift mechanism on my Pioneer PL-41 turntable. I got some incomplete info along the way, so I decided to take the thing apart to see how it really works. It's pretty simple, really. When the cueing lever is set to "down," the weight of the arm and an adustable spring apply downward force onto a piston that goes completely through a small brass/bronze housing. The housing is apparently supposed to be filled with fluid. The piston has two washers attached at its midpoint, to provide resistance to the fluid. Now that I'm thinking about it, perhaps the housing is NOT supposed to be filled with fluid. If the fluid is too thin, I would think it would eventually seep out the bottom, as the piston (as it exits the housing at the bottom) is not a tight fit (it has to slide up and down). Perhaps I need to use a smaller amount of more viscous oil to provide the resistance needed for the tonearm to drop at the correct speed. I'm just unable to locate the original specs for this. Here are a couple pictures. Quote Link to comment Share on other sites More sharing options...
fini Posted August 11, 2011 Author Share Posted August 11, 2011 In this shot you can see the spring that pulls the lifter down, and its adjustment screw. The turntable is obviously upside-down. The small philips bolt in the side of the chamber is, I believe, and oiling access port. Quote Link to comment Share on other sites More sharing options...
fini Posted August 11, 2011 Author Share Posted August 11, 2011 Here's the piston disassembled. You can see the washers afixed to the piston. No seal was present between the chamber and the cap. Any advise or comments would be greatly appreciated. If anyone has access to more information on the PL-41, especially the service manual (I have the owner's manual), I'd appreciate either a copy or a scan of any info on this contained within. Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted August 11, 2011 Share Posted August 11, 2011 What material is the white disc made from? It looks like it uses the friction between the disc and the wall to slow or dampen the mechanism. It's also possible that it uses the air escaping the chamber to do the dampening. Either way, it should fit tight to the brass I would think, does it? Quote Link to comment Share on other sites More sharing options...
fini Posted August 11, 2011 Author Share Posted August 11, 2011 The discs are metal. One is slightly smaller: 0.354" and 0.334". The chamber into which they fit is 0.388". Maybe the air isn't escaping the chamber so much as being forced from one side of the discs to the other? Quote Link to comment Share on other sites More sharing options...
DizRotus Posted August 11, 2011 Share Posted August 11, 2011 I think air is the fluid used to damp the lift. Quote Link to comment Share on other sites More sharing options...
fini Posted August 11, 2011 Author Share Posted August 11, 2011 Neil, Before I took it apart, the arm dropped too fast. Do you think some thick silicone oil (I have some very viscous---300,000 cst---oil) would be the ticket to "slow it down?" Maybe it wells in the bottom and coats the piston? Quote Link to comment Share on other sites More sharing options...
fini Posted August 11, 2011 Author Share Posted August 11, 2011 BTW, here's a brochure I located online. They describe the lift mechanism as "oil damped." Quote Link to comment Share on other sites More sharing options...
DizRotus Posted August 11, 2011 Share Posted August 11, 2011 BTW, here's a brochure I located online. They describe the lift mechanism as "oil damped." Now I don't think air is the fluid used to damp the lift. Nonetheless, before I started filling the cylinder with 10w40. I'd try some petroleum jelly to see what effect it has. It can be easily cleaned away with Isopropyl alcohol (not rubbing alcohol, it contains lanolin) and cotton swabs. Quote Link to comment Share on other sites More sharing options...
fini Posted August 11, 2011 Author Share Posted August 11, 2011 How much petroleum jelly? I have some turbine and air-tool oils, too. Quote Link to comment Share on other sites More sharing options...
DizRotus Posted August 11, 2011 Share Posted August 11, 2011 EDIT: It just occurred to me that the photos show the underside of the turntable. Therefore, transpose each reference to up, down, top, bottom, etc, below to its opposite. The photos suggest that the top of the cylinder is screwed to the cylinder. Is there a tight seal? You don't want extra virgin leaking on your vinyl. I the suspect that lifting the tone arm drives the white rings down in the cylinder with enough force to permit the fluid (whatever it is) to get past the rings into the upper part of the cylinder. The relatively light weight of the tonearm slowly pulls the rings back up. The fluid in the cylinder slowly moves from the upper part of the cylinder past the rings back to the lower part of cylinder. If that system contains a liquid and it's not sealed, it could get messy. Try a small amount of petroleum jelly. You might get lucky. That small amount of friction might be inconsequential when lifting the tonearm, but enough to damp the descent. Quote Link to comment Share on other sites More sharing options...
fini Posted August 12, 2011 Author Share Posted August 12, 2011 I'll give it a shot in the morning and report back. Yes, the end (bottom) "cap" of the cylinder attaches to the cylinder with two screws. There was no gasket, so it's brass on brass. Also, the piston protrudes through the cap. This seems like it would provide a way for a too-thin oil to seep out. Quote Link to comment Share on other sites More sharing options...
JJkizak Posted August 12, 2011 Share Posted August 12, 2011 Looking at that mechanism the oil would have to be on the very thin side in order to leak out over the years. There are a multitude of thin oils available and you should have seen some kind of residue somewhere. You will need an oil that will not "gum up" with temperature and long life. It might even be a viscous fluid like "Dexron III". Any kind of gel will not work. And keep in mind there are no seals, the parts are machined for a perfect fit and one little boo-boo will cause a leak. Maybe just a "skoash" (really tiny amount or the mechanism will take on a twist) of sealant on the upper and lower mating surfaces would help prevent leaking. JJK Quote Link to comment Share on other sites More sharing options...
fini Posted August 12, 2011 Author Share Posted August 12, 2011 JJK, are you saying in your opinion it was filled with oil? BTW, the piston only travels about 1/8" when everything is assembled. Quote Link to comment Share on other sites More sharing options...
JJkizak Posted August 12, 2011 Share Posted August 12, 2011 Yes, but it could be just air with precise seals and if so the seals would have to be replaced. But the advertisement says "oil dampened" I believe. The gel will not last long if it does work on air and will eventually gum up. The .001 wow and flutter is an impossible specification for that time as the best labratory test tape ($300.00) available from Ampex was .003 (non-weighted) and was the industry standard. JJK Quote Link to comment Share on other sites More sharing options...
JL Sargent Posted August 12, 2011 Share Posted August 12, 2011 If it were mine I would try a little light turbine oil. I couldn't imagine it would hurt anything and might be close to the right viscosity. Quote Link to comment Share on other sites More sharing options...
fini Posted August 12, 2011 Author Share Posted August 12, 2011 The downward pressure from the tonearm is quite low (1-2 grams) at the tip. Of course, where it is lifted by the piston is 2/-3/4 of the way back to the pivot (fulcrum). I'm not sure what the force would be at the point of lift. JJK, do you have a recommendation for a type and weight of oil to use? As I recall, when I took the piston apart there was some thin-ish oil residue. Also, what would you use as a sealant? Quote Link to comment Share on other sites More sharing options...
fini Posted August 12, 2011 Author Share Posted August 12, 2011 Thanks for the input, JL. Quote Link to comment Share on other sites More sharing options...
JJkizak Posted August 12, 2011 Share Posted August 12, 2011 I think I would do some online Googling to see maybe what fluids other people have used. That screw also could be a "air bleeder" to get the air out after loading with oil. The threads are possibly very tight and might also be filled with some kind of sealant to prevent leakage. The only reason I suggested to use a sealant on the bottom flange is there are three small screws I believe that fasten it to the main body and any teeny tiny warp will cause a leak. The industry uses machined cast steel and lots of fasteners torqued evenly to prevent leaks. Remember how much effort it took to remove the screws. JJK Quote Link to comment Share on other sites More sharing options...
fini Posted August 12, 2011 Author Share Posted August 12, 2011 I have found no reference to this part of the lift mechanism. It's like no one ever looked under the turntable before. Online, most posters were suggesting dripping 300,000 cst silicone oil down the tube from above. I have found (obviously) that that tube bottoms out and does not in any way connect to this piston chamber. I feel like I'm forging a new trail. Thank God we have smart guys willing to think and entertain ideas here on the Klipsch forum! Actually, only two extremely tiny screws hold the cap on. Here they are next to my fingertip: Quote Link to comment Share on other sites More sharing options...
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