Pioneer PL-560 Strobe flash issue

[Ricktptman]

This has already been posted in the Pioneer forum and received no relevant responses.

Many (but not all, by YT video sample data) of these particular PL-'s have this issue.
I've discovered that it's not the lamp. I went through a (probable) last "spit 'n polish" and maintenance cycle for this venerable 'table that I bought at least fifteen years ago. It's served me faithfully, and I thought it's "now or never" for getting to the bottom of the "flash" issue. You can see it on any number of those videos, it's a very common thing. They might've even done it when they were new-I saw them new, but never thought to look closely at them because I couldn't afford them at the time.

Does anyone have any insight into this particular model with respect to this particular issue?

I did testing on the lamp and the lamp's fine, which was surprising. I used an LED w/resistor in parallel and the LED does it as well, so it's UPSTREAM from there. Any assistance is appreciated! TIA.

 

[shelly_d]

You can download the service manual at Vinyl Engine. You will need an account but it is free and never spams you. I'm at work and don't have my login credentials to take a look at the circuit.

 

[shelly_d]

I have downloaded the manual and looked at the circuit. It is a very simple one for the neon light. It is fed by 150V DC from the power transformer. It is turned on and off by a transistor on the cathode (negative side) of the light. That is transistor Q3, a 2SC1279S. That transistor gets its signal to turn on and off from a switch, S6, on the pitch control. With that switch engauged the limp flickers and works as a strobe, with it disengauged, the lamp does not flicker. I am not sure if the lamp would be steady on or off. Try engaguing and disengauging that switch and watch for the flicker. If it does not flicker or strobe in either position the culprits, in the order of checking are:

1. Dirty switch (use contact cleaner)
2. broken wire or trace feeding the lamp
3. Faulty trnasistor
4 Faulty Oscellator Chip. (The circuit is fed from pin 14 on that chip.

How to pin it down:

Take a sacrificial led, with a small value resistor in series and place the negitive on ground and touch the positive to pin 14 on the oscilator chip. If it flickers, the chip is doing what it should. You are looking at logic voltages at this oin so assume 3 to 5 volts. (If you have an oscope that would be even better). I'm betting that chip is just fine. The transistor is probably good as well. I think the most likely candidate is that switch.

Good luck. Please post back what you find.

Shelly_D

 

[Ricktptman]

Thanks for your reply, shelly_d. It's not 1. or 2. I've already checked and renewed solder traces. I did not do the LED w/resistor test on the direct output of the chip. I'll check into that.
It could be a faulty transistor, I suppose, but generally speaking I've found that they (especially outside of an audio pathway where noise can be a mitigating factor) work or they don't.
But I'll check that as well. I have a scope but when I installed the table I made getting it out of its location harder (captured cables) than I meant to as a security precaution. The scope's a pain to move as well, but I'll see what I can do...

Thanks again!

 

[Victorinox]

Thanks for your reply, shelly_d. It's not 1. or 2. I've already checked and renewed solder traces. I did not do the LED w/resistor test on the direct output of the chip. I'll check into that.
It could be a faulty transistor, I suppose, but generally speaking I've found that they (especially outside of an audio pathway where noise can be a mitigating factor) work or they don't.
But I'll check that as well. I have a scope but when I installed the table I made getting it out of its location harder (captured cables) than I meant to as a security precaution. The scope's a pain to move as well, but I'll see what I can do...

Thanks again!

C5. 22uF250 volt. I replaced that and no more flickering. It was leaking and measured nothing after desoldering.