Yamaha PF 800 arm damping - help needed!

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balthus
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Yamaha PF 800 arm damping - help needed!

Post by balthus » 18 Sep 2019 00:41

I have had a Yamaha PF 800 sitting on my shelf for some time, and am finally getting around to setting it up properly. My issue is with the cueing control. When depressed, the arm will lift slowly. But it lowers very abruptly, with little or no damping at all. The owner's manual states, "...the cueing switch can be used to gently raise and lower the stylus." Both the owner's manual and service manual in their spec sections describe the cueing as "solenoid, oil damper." Solenoid refers to the mechanism that puts the automatic lift at end of record function into motion. Which leaves "oil damper" - evidently the cueing control is oil damped. So why doesn't the arm lower slowly. Thoughts of mine; 1. the owner's manual statement is missing a comma, and should read, "...the cueing switch can be used to gently raise, and lower the stylus" i.e. "gently" only pertains to raising, and not lowering the arm. In this case, it would mean the PF 800 didn't have damping for the lowering of arm... which I find hard to believe in a turntable of this caliber. 2. there is insufficient oil to damp the arm in its downward motion.

Any thoughts on 1. whether the table was meant to have damped lowering of arm? 2. Why it may not be damping when lowering? 3. if there is a way to add oil to some well that isn't mentioned in the service manual, that also doesn't mention the need or method to refill oil?

Thank you!

musicmn
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Re: Yamaha PF 800 arm damping - help needed!

Post by musicmn » 18 Sep 2019 03:19

Hi, I've never serviced this model of Yamaha turntable. But what they mean by damping is that they used either 300,000 wt silicone damping fluid or 500,000wt silicon damping fluid to slow the drop rate of the tonearm. This damping fluid can dry up over time or leak out and get all over everything causing the tonearm to drop like a rock. Usually the damping fluid is put directly on the cue piston which is buried in the mechanism. On some model turntables a trough like part is used to hold the damping fluid. I will take a look at the service manual to see if they at least show the cue piston then maybe I can let you know how to proceed. Unless someone has this turntable and can shed some light on how to replace the damping fluid.

Alec124c41
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Re: Yamaha PF 800 arm damping - help needed!

Post by Alec124c41 » 18 Sep 2019 03:28

Usually, a viscous silicone oil is used to damp arms, in some part that slides on or in another part. In some, there is a piston that slides in a cylinder.
I can only speculate that the rod that supports the lift arm, passing through the sleeve, might be an appropriate place for a drop of this oil. I don't see anything else on the arm view.
Nor can I say what viscosity would be appropriate.

Cheers,
Alec

balthus
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Re: Yamaha PF 800 arm damping - help needed!

Post by balthus » 19 Sep 2019 13:17

Thanks to you both for your insights. I share your view that its likely that the piston/rod supporting the lift arm could use a bath. My frustration was in not seeing where oil could be added from atop the cylinder housing the piston/rod. However, now that I take another gander at the Service Manual "tonearm external view" diagram, I see that the cylinder appears to have a small nut at its base, by which means the cylinder can be separated from the lift arm, and that the nut also then can be removed from the base of the cylinder. If so, I think it likely I could add oil from the underside of the cylinder. I will update within a day or two, if you're curious how it turns out. If any oil remains inside the cylinder allowing me to get a feel for the viscosity, I will try to match it... if not, I will probably go with a medium weight motor oil. I'm not too concerned about the arm descending at a leisurely pace... thanks again.

musicmn
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Re: Yamaha PF 800 arm damping - help needed!

Post by musicmn » 20 Sep 2019 01:24

Hi balthus, In tonearm external view page 12 you can see a set screw (number 6) that holds the cue cylinder in place. All I believe you need to do is to loosen that set screw and remove the entire Cue mechanism so it can be serviced. Once you have it out then it can be taken apart to be cleaned and have new damping fluid put back in. As you disassemble it take some pictures of it so you use them to help you get it back together correctly. Motor oil of any weight will not work it's just to light of a viscosity and will just drip out all over everything. You need to get the silicone damping fluid I recommended in my other post to get the tonearm to drop nice and slow to a record. If the cue piston in this turntable is like other ones I have seen you will find one to three grooves in the cue piston. That is where a small amount of the silicone damping fluid is placed. Then the piston is put back into the cylinder and turned and pushed up and down to spread it evenly over the piston. Then assemble it and install Cue mechanism back into the tonearm and check the drop rate of the tonearm. The nut you see on the bottom of the piston is just used to adjust height of the cue elevator not to add damping fluid. From what I can see of the tonearm used on this turntable I would use 300,000wt silicone damping fluid. I think the 500,000wt would be to thick. I hope this helps.

balthus
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Re: Yamaha PF 800 arm damping - help needed!

Post by balthus » 02 Oct 2019 02:43

Thank you for your guidance! Loosening the set screw was easy enough, as it is entirely missing, lol. (and where I'd find such a tiny screw to replace it, idk.) The difficulty came in removing the cue mechanism. The piston could not be pushed upwards through the cylinder to remove it, as the piston passes through the spring at the base, and is restricted from passing upwards by a small clip at its base (conveniently not shown in Tonearm External View 15-4). The clip has four tiny prongs holding it in place, and I fear that if I attempt to remove it, I will never succeed in getting the spring and clip properly back in place. If I were planning to keep the table, I could probably convince my friendly neighbor whose hobby is tweaking the innards of valuable, antique cameras to give it a crack, but since I plan to sell it, I think I will leave it to the next owner to deal with (especially as the table has some cosmetic issues that also undermine its value). As it stands, it works well as a semi-automatic table (manual start and automatic lift at end of play) and perhaps the next owner will be satisfied with that compromise. Thanks again for your help I will be listing the table on usaudiomart should you know someone who might be in the market. Cheers!

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