Thanks - I was referring to the "speed control knob" though. The trim pots underneath are already Bourns units.
Yamaha YP-D6 Pulsing Speed - Rebuilt - Parts List - SOLVED YAAAAYYY
- Thread starter Johnny_Law
- Start date
Thanks - I was referring to the "speed control knob" though. The trim pots underneath are already Bourns units.
stratokaster
Mental toss flycoon
Just a thought....
Does this turntable use zener diodes as voltage references?
Does this turntable use zener diodes as voltage references?
Yes! There is one zener in the power supply and two in the servo. I think I measured the voltage across each under operation before but now that I think about it, I don't think I've measured the voltage drop across each before / after a speed jump.
Hmm. This guy's YP-D8 was experiencing similar (although pretty different) symptoms - solved by a rebuilt power supply that presumably included a new zener diode? https://audiokarma.org/forums/index.php?threads/yamaha-yp-d8-direct-drive-turntable-inconsistent-rpm-solved.778177/
stratokaster
Mental toss flycoon
I think zeners in the servo are more important. If the voltage reference drifts, the speed would probably also drift.
Try to find temperature-compensated replacements if possible.
Try to find temperature-compensated replacements if possible.
Man one hell of a thread!
Don't know the table but am following along now, great read and well done so far!
New zener diodes are in at D5 and D7 on the servo board.
So far so good (a couple records) but let's see what happens tomorrow.
So far so good (a couple records) but let's see what happens tomorrow.
This morning, it started up too fast. I gently lifted it up and put my finger on D6/D7 ... it immediately reduced speed to normal. I have a 1N4148 I can put in place of D6 (VD-1122), but I'm curious @stratokaster what is a temperature-compensated zener diode, and does it seem like there's an issue here?
Note that originally there was a tan colored rubber encasing covering both D6 and D7, but I had to break it apart to put in the new D7. Should I re-apply some kind of encasing, maybe black silicon RTV which I have on hand?
This is an old pic of the servo board that I posted earlier, before I replaced any diodes (and before I replaced the trimmers, etc). You can see the tan-colored stuff covering D6 and D7 (and other diodes).
Note that originally there was a tan colored rubber encasing covering both D6 and D7, but I had to break it apart to put in the new D7. Should I re-apply some kind of encasing, maybe black silicon RTV which I have on hand?
This is an old pic of the servo board that I posted earlier, before I replaced any diodes (and before I replaced the trimmers, etc). You can see the tan-colored stuff covering D6 and D7 (and other diodes).
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stratokaster
Mental toss flycoon
Some zener diodes have very low temperature-associated drift. For example, Microsemi produces a number of mil-spec zeners that have temperature coefficient as low as 0.001% per 1 degree C, maybe even lower (I don’t have the datasheet at hand).
I think that gooey stuff was put there to keep the diodes nice and toasty and reduce the warm-up time (and the associated drift).
I also think that they used a zener in series with a diode instead of a single higher-voltage zener in the hopes that these two parts would compensate for each other’s drift. So in theory you could replace them both with a single low tempco zener of higher voltage...
I think that gooey stuff was put there to keep the diodes nice and toasty and reduce the warm-up time (and the associated drift).
I also think that they used a zener in series with a diode instead of a single higher-voltage zener in the hopes that these two parts would compensate for each other’s drift. So in theory you could replace them both with a single low tempco zener of higher voltage...
Thanks! I'll definitely look into those temp-stable ones. I confirmed that the speed is too fast until I hold D7 between my fingers for maybe 5-10 seconds, then it comes down to correct speed. When I let go, it goes back up (slightly at first - seems like a function of temperature but can't be 100% confident). I could try applying some RTV in the meantime to D6 & D7 together, but it sounds like those tempco zeners are the ticket.
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Maybe something like this? https://www.mouser.com/datasheet/2/427/zpy3v9-108163.pdf
stratokaster
Mental toss flycoon
Those look appropriate for the task
Thanks, noted. Update is I've found that the same happens when D6 is heated between fingers. I wonder if I should swap in a 1N4148 to see if that changes anything.
stratokaster
Mental toss flycoon
That could help.
Alternatively, maybe measure voltage across both D6 and D7 and replace them with one zener?
Alternatively, maybe measure voltage across both D6 and D7 and replace them with one zener?
Well ... after two days of playing, I think it's time to put this to bed. Finally. After having declared it solved what, like 5 times?
I had replaced D7 but was still getting speed issues, especially if I touched, moved, or held D6 (a VD-1220). So I replaced D6 with a 1N4148, and things were much better. However, the speed still drifted more than I liked. So I touched / moved / held D8 (the double diode VD-1220) and the speed also drifted. I replaced D8 with two 1N4148 in series, and also replaced for good measure D10 (VD-1121) with a 1N4148 as well.
After re-adjusting the trim pots, the speed is rock solid no matter what, from record to record back to back, or after hours of off time, including first thing in the morning after sitting overnight. There's no more speed pulsing, no more drift.
While I was debating replacing those diodes, I did some research and found that the circuit with D6 and D7 in parallel, with D7 reverse biased, in a common method of voltage regulation (in this case it regulates the base of TR13). See https://www.electronics-tutorials.ws/diode/diode_7.html and https://www.allaboutcircuits.com/textbook/semiconductors/chpt-3/zener-diodes/. It also appears that Yamaha designed this circuit to be immune to temperature deviations, since 5.6V zener diodes have a near-0 temperature coefficient:
Both below images credit to https://www.electronics-tutorials.ws/diode/diode_7.html, the below is the example used to illustrate use of a zener diode as a voltage regulator:
and
Look at the D7 circuit in on the Servo board ... look familiar?
So my hypothesis is that although all of the original diodes had degraded somehow to become significantly temperature-sensitive, it was really D6 that was causing improper voltage supply to the base of TR13, thus causing errant and inconsistent current to the motor. Advice to anyone in the future is to replace all those old diodes!
I had replaced D7 but was still getting speed issues, especially if I touched, moved, or held D6 (a VD-1220). So I replaced D6 with a 1N4148, and things were much better. However, the speed still drifted more than I liked. So I touched / moved / held D8 (the double diode VD-1220) and the speed also drifted. I replaced D8 with two 1N4148 in series, and also replaced for good measure D10 (VD-1121) with a 1N4148 as well.
After re-adjusting the trim pots, the speed is rock solid no matter what, from record to record back to back, or after hours of off time, including first thing in the morning after sitting overnight. There's no more speed pulsing, no more drift.
While I was debating replacing those diodes, I did some research and found that the circuit with D6 and D7 in parallel, with D7 reverse biased, in a common method of voltage regulation (in this case it regulates the base of TR13). See https://www.electronics-tutorials.ws/diode/diode_7.html and https://www.allaboutcircuits.com/textbook/semiconductors/chpt-3/zener-diodes/. It also appears that Yamaha designed this circuit to be immune to temperature deviations, since 5.6V zener diodes have a near-0 temperature coefficient:
Both below images credit to https://www.electronics-tutorials.ws/diode/diode_7.html, the below is the example used to illustrate use of a zener diode as a voltage regulator:
and
Look at the D7 circuit in on the Servo board ... look familiar?
So my hypothesis is that although all of the original diodes had degraded somehow to become significantly temperature-sensitive, it was really D6 that was causing improper voltage supply to the base of TR13, thus causing errant and inconsistent current to the motor. Advice to anyone in the future is to replace all those old diodes!
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stratokaster
Mental toss flycoon
Congratulations 
tballinger
Active Member
Folks,
Thank you so much for this thread! My YP-D6 is suffering from drifting timing, but nothing dramatic or pulsing in it's behavior. After reading this thread I'm thinking I may be able to replace D6/D7 with 1N4148 diodes, but I want to be sure I'm following this all correctly. Am I right in thinking that this linked part below is what I need to replace diodes on this servo board?
https://www.mouser.com/ProductDetail/ON-Semiconductor-Fairchild/1N4148?qs=i4Fj9T/oRm8RMUhj5DeFQg==
Thanks in advance!
Tony
Thank you so much for this thread! My YP-D6 is suffering from drifting timing, but nothing dramatic or pulsing in it's behavior. After reading this thread I'm thinking I may be able to replace D6/D7 with 1N4148 diodes, but I want to be sure I'm following this all correctly. Am I right in thinking that this linked part below is what I need to replace diodes on this servo board?
https://www.mouser.com/ProductDetail/ON-Semiconductor-Fairchild/1N4148?qs=i4Fj9T/oRm8RMUhj5DeFQg==
Thanks in advance!
Tony
I used 1N4148 at D6 and zener diode 512-BZX79C5V6T50A at D7.
Here's my whole parts list which I am 90% sure is accurate ... C8 I forget if I ran a 4.7uF (the value of the originally installed component) or a 47uF (as specified by the circuit diagram).
Here's my whole parts list which I am 90% sure is accurate ... C8 I forget if I ran a 4.7uF (the value of the originally installed component) or a 47uF (as specified by the circuit diagram).
tballinger
Active Member
This is very helpful, thanks so much. I'm not sure if I can really accomplish this — but I can at least open it up, have a look around and have the parts ready if I think I'm to the task.
Thanks again,
Tony
Thanks again,
Tony
Good luck!