PL1200A (PL51A?) speed/effective length questions

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Bohuweno

PL1200A (PL51A?) speed/effective length questions

Post by Bohuweno » 29 Jun 2019 06:54

I have a PL1200A that I acquired recently. From what I can tell, this Japan model is identical to PL1200A. As with most old decks I buy, it was cheap. The cosmetic condition is very good, but it had audible speed problems in the form of widely fluctuating speed from initial playback. This settled down a bit with a bit of manipulation of the adjustable speed controls (that you use with the strobe), but every time it's switched on again, the speed needed readjustment with the speed controls and using the strobe as a visual guide. I've gone back and forth between 33 and 45 as well, to see if that helps at all, but it doesn't seem to make any difference.

The wide fluctuation (audible) returned during a second playback session, so I've removed the base panel and squirted contact spray into the variable resistors for the speed controls. Also gave the 33/45 switch a shot. So far, it seems to play back quite well, it's better at settling into about the correct speed (according to strobe) when I turn on the power, but does tend to still drift slightly after a minute or so, and I then need to adjust to the right speed. I haven't noticed any consistent pattern in the player always running too fast or always too slow; just one or the other.

I think I read somewhere that the next step after the variable resistors is to clean any crud out of the motor. That would be a new step for me, I haven't touched a turntable motor before. Is it worth experimenting with the motor fine speed adjustment screws first? This is mentioned in the service manual for "when fine adjustment of the speed control does not give a satisfactory speed". I am assuming not if I'm trying to fix inconsistent speeds.

On a different topic from playback speed, I bought this deck without a headshell. I got a new headshell for it that looks right and is supposed to be suitable for S-arm decks such as old Pioneers among other brands. What I can't work out is the specified effective arm length of my deck: the owner's manual says 221 mm, with the cartridge overhang specified as 15.5 mm. The closest I can get to 221 mm with this or the other headshell I tried is 224 or 225 mm. An exact measurement is difficult to make. However, with this length, an overhang of about 15.5 is achieved, if I try to gauge the distance between the spindle and where the stylus tip would be in relation to the spindle with the arm all the way across to the spindle.

When it comes down to it, I don't believe I have the wrong size headshell. The main body section (the black part) is 54 mm by my measurement, the barrel (according to the seller is 12 mm). With the cartridge mounted about where you would expect it to be in the headshell, the overhang seems correct. Attempting to move the cart back to get to the 221 mm effective length, in this or the other headshell I tried, means the cartridge looks wrongly positioned and is also awkward because the terminals of the cart and the headshell pushed right up to each other. Has anyone else encountered this? For the moment I'm just going to assume my overhang is close to correct, and do the final alignment with a protractor.

Alec124c41
vinyl engineer
vinyl engineer
Canada
Posts: 23196
Joined: 28 Oct 2002 03:24
Location: North of Toronto, Canada

Re: PL1200A (PL51A?) speed/effective length questions

Post by Alec124c41 » 29 Jun 2019 12:34

Clean the power switch, too.
Use a protractor to align the cartridge. This will set both the correct angle and effective length. Do not then try to adjust to any other length or overhang..

Cheers,
Alec

Bohuweno

Re: PL1200A (PL51A?) speed/effective length questions

Post by Bohuweno » 29 Jun 2019 13:08

Alec124c41 wrote:
29 Jun 2019 12:34
Use a protractor to align the cartridge. This will set both the correct angle and effective length. Do not then try to adjust to any other length or overhang..
Thanks for that. I've downloaded a protractor from Vinyl Engine and aligned the cartridge now.


The speed stills seems to wander, so I'll clean the power switch as the next step, as you suggested.

An incidental question, not for this deck only. I notice that when you lift and lower to a record using the cueing arm, it may drop straight down, but will commonly skew to one side when lifted again. I assume in a perfect setup you can pretty much lower and lift and lower onto the same position repeatedly. What adjustment can be made to deal with that? Is it the antiskating? I've set the Pioneer up as instructed by the manual: there is a lateral balance weight, and it simply says to set the weight inward by 10 to 15 mm from the end of the horizontal shaft that holds it. When I got the deck, it was 15 mm in, so I didn't touch it. All the other setup is according to the cartridge manufacturer's recommendation, and I set the tracking force with a stylus force gauge. Alignment with a protractor as stated above.

Bohuweno

Re: PL1200A (PL51A?) speed/effective length questions

Post by Bohuweno » 29 Jun 2019 14:17

From what I can tell, this Japan model is identical to PL1200A.
That didn't make sense! What I meant to say was that my Japan model PL1200 looks to be identical to the PL51A in other markets.

Alec124c41
vinyl engineer
vinyl engineer
Canada
Posts: 23196
Joined: 28 Oct 2002 03:24
Location: North of Toronto, Canada

Re: PL1200A (PL51A?) speed/effective length questions

Post by Alec124c41 » 29 Jun 2019 19:40

The antiskate exerts a slight outward force on the arm. What keeps it from moving when raising and lowering is friction in the mechanism. IOW this is a very common phenomenon, and not something to worry about,

Cheers,
Alec

Bohuweno

Re: PL1200A (PL51A?) speed/effective length questions

Post by Bohuweno » 30 Jun 2019 02:13

It's not so much that I worry about it as I would like to prevent it if there's an easy fix.

Bohuweno

Re: PL1200A (PL51A?) speed/effective length questions

Post by Bohuweno » 01 Jul 2019 15:25

I got to the two switches (speed selector and power switch) today. The problem is that the cases are secured with two rivets each. I don't know if any contact spray really entered the case when I attempted to find an opening. After reconnecting the player and testing the speeds, they aren't fixed yet.

It looks like the next step is to drill out the rivets to get the switch open - at least that's what some people say they do for riveted microswitches. When it comes to putting the case back together, someone (not in relation to this turntable) suggested using a machine screw and nut instead. Sounds good as I certainly don't have any experience with riveting, or the tools to do it. The problem here is that the two microswitches screw onto a metal plate (two screws for each switch, with each switch mounted on its own plate). That makes it difficult to add a screw and nut where the rivet holes are. I don't want to go as far as attempting to drill new holes in the plates, it would need precision, the metal might be steel, and removing the plates is going a bit further than I want right now.

I wonder how other people with Pioneer decks handled this? It looks as if the two screws that mount the switches to the plates would be sufficient to hold the case together. Has anyone done that?

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