Turntable Repairman

My turntable is "linear tonearm" which means instead of the tonearm being on a pivot, it's on a servo-driven shaft that moves the whole tonearm inwards as the stylus moves.  This reduces the tracking error and allows for a shorter tonearm, which is less massive and has a lower resonant frequency.

Or something like that.

Mostly it's one more thing to go wrong.

This week my turntable has decided to play track 1 of any LP I'm trying to dub, then gets about halfway through track 2 and starts skipping.  After track 3 it starts playing fine again.  In my old Sony SL-10 turntable the tonearm moved along a rotating shaft, and that shaft needed to be lubricated every couple of years.  I was used to doing that. I figured my new turntable had a dry spot, right?

My replacement turntable is a Sony PS-FL7, and the shaft the tonearm rides on does not rotate.  It also requires complete disassembly to get to it.  I tore it down and cleaned up the shaft and very carefully relubricated it.

Reassembled.  Tested.

Did not fix.  Grrrr.

Disassembled again, checked all the mechanicals.  The servo that controls the tonearm position runs on a worm gear.  Although the fast-forward and fast-return controls move the arm just fine, the arm gets stuck when being pulled slowly across the record surface by the progress of the stylus.  Checked the worm gear for missing teeth (none).  The worm gear looked pretty well lubricated with a white grease, but I've always had good results with my black molybdenum grease so I cleaned off the white stuff and relubricated.  

Reassembled.  Tested.

Not fixed.  Grrrr.

Disassembled again.  Checked the mechanicals again.  Discovered (this was actually on about the sixth disassembly) that the wiring harness to the cartridge snakes off the back of the tonearm, in an S-shape.  At the far edge of the record, it's tucked into the mechanism.  At the inside edge of the record it's stretched out taut.  In between, it bows out as the arm moves and between tracks 2 and 3, it contacts the inside back of the case.  There is apparently JUST ENOUGH resistance from that contact to hang up the tonearm as it tries to move across.

Lubricated the case with some grease where the cable contacts it.

Reassembled.  Tested.

Not fixed.  Grrrr.

The cables are held in place with little flexible padded metal strips.  Tried rebending the cable stays to keep the cable off the back wall.

Reassembled.  Tested.

Not fixed. Grrrrr.

Did I ever mention how much I hate vinyl records?

COMPLETELY rerouted the cables, so they move now without touching the case. Only took three more disassemblies.

Testing now.

Not fixed. Grrrr.

DO you have a small belt or two on the turntable? Some of the old TTs had them, and they can go bad after a couple or three decades. That's the only thing that comes to mind after all that you've been through.

If you don't mind: as a general rule, it's a bad idea to change the type of lubricant that a device came with from the factory. It sounds as if it had lithium grease, which is all liquid, and you replaced it with "moly lube," which can easily be ten percent solids. As a mechanic, I used lots of moly as assembly lube (and still have some in my toolbox), and it is great for that, but I never use it on lightweight applications. I would suggest that you replace your lubricant with the factory product, or general purpose lithium grease if you can't identify the factory lubricant.

There's one little belt (abut 3/4" long) that appears to be fine.  There's also a tensioned string that wraps around two opposing pulleys, and that appears t be fine too.

Neither of those would explain hanging up 1" into record, but not elsewhere, so far as I can figger.  But hu nose: I ain't at an answer yet.

And I wiped all the grease off the wires & case, since that was ineffective.  The amount of grease on the worm is minuscule.  But thanks for the warning -- I don't think I have any lithium grease. Will have to get some.

My latest theory(?) is maybe there's a burr on the underside of the guide rod, where you can't see it. I plan to disassemble and run a strip of sandpaper along it, then relubricate with 3-in-1 oil. But not today.

I had a similar problem on a turntable with a standard design arm, and it drove me nuts until I found the problem (wiring). So out of curiosity, I spent some time looking for your problem on forums, and the closest I could come was not the exact model of Sony, and not the 100% exact problem - but damned close - and in the three cases I found that had a solution, the problem was a very small belt, like a rubber band.

_Howard wrote:

DO you have a small belt or two on the turntable? Some of the old TTs had them, and they can go bad after a couple or three decades. That's the only thing that comes to mind after all that you've been through.

...the three cases I found that had a solution, the problem was a very small belt, like a rubber band.

When all else fails, listen to your Uncle Howard.

It was the belt.

I put this project aside for two weeks while I played with my new subwoofer, but when I came back to it, it was right where I'd left it.  Lubricating the traveler bar did nothing.  So I removed the belt, took it into Ace Hardware, and came home with a 15/16" rubber O-ring for 79¢.  Seems to have fixed it.

Yay.  Thanks Howard!