Pioneer PL-540 Questions

[boreas]

I just picked one of these up and, while it's for the most part in decent shape, there are a couple of things that I'd appreciate some help with.

First, and probably simplest (at least to answer), the tonearm stub is lose, probably from shrinkage in the resonance damper that separates the stub from the gimbals. I theorize that the stub is held in place by a screw accessible only by removing the tonearm from the horizontal pivot post. Is this correct?

Second the strobe light blinks noticeably, about 4 times a second at 33-1/3 and much faster at 45, way more than the ~150% faster you'd expect if it were consistent with the increase in platter speed. Speed accuracy is acceptable if not perfect, about 33.5 +/- .03 and 45.15 +/- .05. Any guesses as to why this is and what the fix would be?

Thanks.

John

 

[boreas]

Well, I solved the droopy stub by wrapping some monofilament in the space between the stub and the damper. It tightened it up considerably and is essentially invisible.

Still looking for some guidance on the blinking strobe.

TIA,
John

 

[EngineerNate]

I'm not sure about that gen of Pioneer, but some of them have an allen key inside the stub behind the little rubber piece that makes the counterweight catch work.

 

[boreas]

The stub is indeed a tube with a rubber plug in the end. Upon removing the plug I was able to see a sort of clothes pin spring in there which has a bulb on one end that fits into and protrudes through a hole in the stub as the indexing point for the helix inside the counterweight. I saw no evidence of a screw beyond the spring. I was able to see a hole in the gimbals that lined up with the stub and probably contains the screw which secures it but it would be necessary to disassemble the gimbals and maybe desolder the tonearm wires to get at it. In the meantime, I effected a quick and dirty fix described in post #2 above.

John

 

[boreas]

Still struggling with the blinking strobe. Not knowing what else to do, I got another bulb in eBay but that exhibits the same problem of blinking 4 times a second on 33-1/3 and too fast to count on 45. Is there a resistor that I should be looking at? The board where the strobe attaches has several resistors and capacitors on it, one or more of which might control the strobe. Also, it looks like I'm not the first to be inside this thing. All the wires that attach to this board are soldered in place rather than wound on the pins as if they had been removed and replaced.

Any ideas?

John

 

[vman96]

John,
I would recap the unit first, there is good possibility that one of the caps not doing it job, after all those years.. Besides the table will benefit in a long run..

 

[boreas]

John,
I would recap the unit first, there is good possibility that one of the caps not doing it job, after all those years.. Besides the table will benefit in a long run..

That's pretty much where I am now. The section of the SM that covers the strobe is reproduced below.



And the schematic is here.



I'm hoping it's not a bad frequency divider. That smells like a proprietary IC to me.

The platter braking is hors de combat too.

John

 

[vman96]

I see what you're saying.. Well, the service manual will help to troubleshoot specific circuitry/components.
If you'll get stock with it, I'd suggest posting this on Pioneer forum; there are more than few individuals very proficient in Pioneer equipment will give you a hand!

 

[boreas]

Update: I remembered seeing that AK sponsor Organ Donor Parts had a PL-540 they were parting out so, after looking for the power supply board and not seeing it, I emailed them to ask whether they had one that hadn't yet been listed. They did so I bought it for a very reasonable price. They shipped the board very quickly and tossed in another board, the oscillator assembly, as well.

Last night, I swapped out both boards and fired the turntable up. The strobe behaves perfectly now and the speed is still very accurate and steady, varying between 33.44 and 33.49 R.P.M on my iPhone app. Next step is to give it a listen and, if all's okay, I plan to veneer it, probably in walnut.

Hurray for ODP!

John

 

[ghazzer]

Well done! You are resourceful & persistent, and your memory is still hanging in there.

 

[boreas]

It is?

 

[boreas]

Ii works! No problems in the signal path. It sounds very good too.

John