Yamaha PF-800 auto stop - need help!

[RunOutGroove]

I wonder if anyone here knows about this table and might have some kind of secret method for setting the auto stop on this thing...? The auto stop feature works perfectly on maybe 90% or more of my records, but there's just a few where the run time is a bit longer and the grooves go closer to the label in the middle and with those ones the auto stop will kick in just a bit before the actual end of the record. If I adjust the auto stop to kick in a bit later, it doesn't kick in at all and the record will just keep spinning until I pull the tonearm off and turn off the motor of the thing. The sweet spot to where the tonearm will pick up and the motor will stop on a record with very little space between the last part of the grooves and the label just doesn't seem to exist. Is this then just a flaw in the design or is there something wrong with the table that prevents me from dialing in the right setting... or is there some way to really fine tune that setting that isn't addressed in the manual?

 

[Hajidub]

Moving the tonearm to desired spot, with adjustment to 10 then backing off knob till indicator lights doesnt work?

 

[RunOutGroove]

Moving the tonearm to desired spot, with adjustment to 10 then backing off knob till indicator lights doesnt work?

Yeah, that's the method that I started with and it works for 95% of records, but not the few where the run time is longer and goes really close to the label. After messing with that method unsuccessfully, I did some extra fine tuning with that dial moving it what seemed to be only fractions of a degree at a time and even with all of that I couldn't get it to work with those "5% records." It would either pick up too early or not at all.

I wonder if the thing just isn't designed well enough to work with all records?

 

[Beobloke]

Sadly, there's not much you can do about it, as the Yamaha system merely relies on the position of the tonearm, rather than working using the increase in arm movement speed due tot he run-out groove.

It's a simple and non-contact system, which is good, but it does have its limitations; as you've found!

 

[RunOutGroove]

Sadly, there's not much you can do about it, as the Yamaha system merely relies on the position of the tonearm, rather than working using the increase in arm movement speed due tot he run-out groove.

It's a simple and non-contact system, which is good, but it does have its limitations; as you've found!

Yeah, that's what I figured. I wish that they had at least designed the thing with some kind of defeat switch so that you could engage it and have it work fully manual. As it is, if you want to do that you have to mess with the auto-lift setting and then re-set later. Like I said, it isn't an issue on most records and the ones where it is, it seems to pick up where there is only 30 seconds or less of the record left, but it's still annoying.

You would maybe have thought that the engineers who designed the thing would have combed through their record collections to find an album that had the longest run time and to test it with that...

 

[Johnny_Law]

Mine has a mind of its own that leads me to believe the transistor driving the circuit may be messed up. After a few rounds of deoxit to the pot, it still randomly decides to go red and pick the arm up regardless of adjustment.

 

[RunOutGroove]

Mine has a mind of its own that leads me to believe the transistor driving the circuit may be messed up. After a few rounds of deoxit to the pot, it still randomly decides to go red and pick the arm up regardless of adjustment.

Ugh! A lesser severe case of this could be my issue. This is exactly why folks like manual TTs, though I'm kind of addicted to the convenience of the auto-stop (great for falling asleep to music!). I hate to spend more money on this stuff and to go without a turtable, but next time I'm near the audio shop in my neighborhood, I'll stop in and ask if they've ever done a repair of such a thing. From what you say, it might just be a case of swapping out a transistor, no?

 

[Johnny_Law]

Based on my rudimentary understanding of the circuit (which I'll copy below), when the sensor is triggered, it grounds out the PTR signal which runs into the OpAmp's inverting input and causes the OpAmp to activate the 2SC1983 arm lift solenoid transistor, which lifts the arm.

So potential errors could be in the LED, the sensor, the potentiometer, the OpAmp, or the transistor ... at least from what I can tell.

Of those things, assuming a clean pot, I would suspect the transistor as the next most likely culprit, but that's just a hunch. I don't know if anyone's ever had a verified issue with that transistor before.

 

[RunOutGroove]

Based on my rudimentary understanding of the circuit (which I'll copy below), when the sensor is triggered, it grounds out the PTR signal which runs into the OpAmp's inverting input and causes the OpAmp to activate the 2SC1983 arm lift solenoid transistor, which lifts the arm.

So potential errors could be in the LED, the sensor, the potentiometer, the OpAmp, or the transistor ... at least from what I can tell.

Of those things, assuming a clean pot, I would suspect the transistor as the next most likely culprit, but that's just a hunch. I don't know if anyone's ever had a verified issue with that transistor before.

View attachment 2869757

Yeah, I barely know enough about the workings of electronics to know that I'm even looking at a schematic, let alone have the ability to read one...