zx-9 speed slows

[jazzgene]

Hi,

I noticed that my zx-9 tape speed slows as the deck plays. The drift is 0.6%per my T-100 analyzer. Most probably won't notice but I have absolute pitch... So it is a big deal for me. And none of my other Nak decks have this issue.

I thought it might be heat related with the capstan motor but when you play a tape and stop and leave the deck on, the speed drifts back up again. And then as you play a tape, it slows down. Anyway, the capstan motor is always running when the deck is on.

This is not an issue where the old lube heats and slows the deck until it stops. This drift range I observed is 0.6% and it takes about 90 minutes of tape play to slow down this much.

Any ideas? This deck was throughly tested and restored by a great tech and I don't blame him for not catching this. But the fact is this issue is here and if my 680zx, MR-1, Dragon, and even my lowly Tascam deck don't have this issue... Well, I can't imagine everything is right with the ZX-9.

Any ideas?

[braxus]

Sounds like one of the motors is going. One of our members here had a similar issue with his DR-1 and it was a motor issue.

[Dimitar Georgiev]

Hi,

I noticed that my zx-9 tape speed slows as the deck plays. The drift is 0.6%per my T-100 analyzer. Most probably won't notice but I have absolute pitch... So it is a big deal for me. And none of my other Nak decks have this issue.

I thought it might be heat related with the capstan motor but when you play a tape and stop and leave the deck on, the speed drifts back up again. And then as you play a tape, it slows down. Anyway, the capstan motor is always running when the deck is on.

This is not an issue where the old lube heats and slows the deck until it stops. This drift range I observed is 0.6% and it takes about 90 minutes of tape play to slow down this much.

Any ideas? This deck was throughly tested and restored by a great tech and I don't blame him for not catching this. But the fact is this issue is here and if my 680zx, MR-1, Dragon, and even my lowly Tascam deck don't have this issue... Well, I can't imagine everything is right with the ZX-9.

Any ideas?

Hmm, I have only one guess - bad capstan motor. Could be Hall element (THS104) which would need replacement.

D.

[jazzgene]

Thanks for your replies. I took a look at the service manual.

I see that the motor is not crystal referenced. It has an oscillator section which the motor uses to sync the rotation speed by using FG servo at the capstan.

I wonder if I replace all the components in the oscillator section, it might fix it? hmmm... I would hate to have to replace the capstan motor.

[Dimitar Georgiev]

I wonder if I replace all the components in the oscillator section, it might fix it? hmmm... I would hate to have to replace the capstan motor.

It would be a good starting point. Are there orange caps in the oscillator section ?

D.

[jazzgene]

It would be a good starting point. Are there orange caps in the oscillator section ?

D.

Don't know. I'll have to take a look. I'll report back.

[jazzgene]

It would be a good starting point. Are there orange caps in the oscillator section ?

D.

There are some orange caps. It is on the D/D motor control PCB.

I've also found out this issue is not so uncommon in many different Nak models.

[Scorpion8]

Either the orange cap issue, or a variable resistor in the speed control circuit is going and changing tolerance as it heats up. Question: when it slows and looses speed at the end of a tape, if you pop another tape in does it start off slow, or does it pick back up to normal speed and then slowly slow down again? That would give you a clue if it's a heat issue, since once the tolerance changes due to heat, it should be "off spec" from that point onward.

[jazzgene]

Either the orange cap issue, or a variable resistor in the speed control circuit is going and changing tolerance as it heats up. Question: when it slows and looses speed at the end of a tape, if you pop another tape in does it start off slow, or does it pick back up to normal speed and then slowly slow down again? That would give you a clue if it's a heat issue, since once the tolerance changes due to heat, it should be "off spec" from that point onward.

Here is the scenario:

1. turn on deck. play 3khz tape. speed is about 0.3 % fast.
2. play a 45 min side of a tape. speed is now about 0.1% fast.
3. play another 45 min side. speed is now about 0.2% slow.
4. stop tape but DO NOT turn off deck. (capstan is still running)
5. wait 15 min or so, now the deck is about 0.2 % fast.
6. so it goes. The deck seems to slow down only during playback of tape. When just idle, upon playback, the speed is back up a bit only to drift down a bit with a tape playing.

I heard this is a common problem with some Nak models. Most people never catch this as the range of about 0.5 % in speed difference is subtle for most. I hear it right away unfortunately and need to get this fixed.

[Nakdoc]

Replace the single orange cap on the motor drive board.

[jazzgene]

Replace the single orange cap on the motor drive board.

Thanks for the response. That is C516 1200pF 100v 2% cap, right?

Will I need to adjust the gain trimmer (VR502) afterwards?

[Nakdoc]

Yes. You only need a 50 volt poly cap. This sets the time constant for the sample and hold, so you will need some sort of speed reference to reset it.

[jazzgene]

Yes. You only need a 50 volt poly cap. This sets the time constant for the sample and hold, so you will need some sort of speed reference to reset it.

Darn, I don't have a 1200pF cap handy. Will have to order.

I have a 3kHz (acutally 3.0019kHz) tape along with T-100. My concern is that with a ZX-9, along with the tape speed trimmer, it has a gain trimmer or what some call symmetry trimmer. These 2 work hand in hand to set speed and least amount of w/f. Will I need to adjust both or can I get away with just resetting the speed with the speed trimmer?

Thanks.

[Nakdoc]

Darn, I don't have a 1200pF cap handy. Will have to order.

I have a 3kHz (acutally 3.0019kHz) tape along with T-100. My concern is that with a ZX-9, along with the tape speed trimmer, it has a gain trimmer or what some call symmetry trimmer. These 2 work hand in hand to set speed and least amount of w/f. Will I need to adjust both or can I get away with just resetting the speed with the speed trimmer?

Thanks.Just the speed control. Symmetry is to balance the two motor drive stages. There are no instructions for setting this!

[jazzgene]

Just the speed control. Symmetry is to balance the two motor drive stages. There are no instructions for setting this!

While waiting for my caps to arrive, I took a look in the service manual.

The service manual does have a blurb on using this gain trimmer. Cool.

I see in my ZX-9, the C516 is not an orange drop cap. It is not original and someone installed a cap way off spec. The service manual calls for 1200pF but the one there now is 2200pF.

Hopefully, I can fix this problem. It makes me sad to see a ZX-9 out of commission in my collection. The 680ZX is playing now to comfort my heart.

[Nakdoc]

That larger value would change the sample/hold time constant, probably drifts because it doesn't fully discharge the cap.

[jazzgene]

That larger value would change the sample/hold time constant, probably drifts because it doesn't fully discharge the cap.

arrrggh, the shop I ordered the caps from sent it to a wrong address... Hopefully this weekend, I'll have the caps.

[jazzgene]

The 1200pF (C516) cap made the deck go way too fast. A 3kHz tape plays at 5kHz and the VF501 speed trimmer does not have enough range. I now believe the service manual is wrong. It won't be the first time a Nak service manual is wrong.

I'll have to source a new 2200pF cap and see if the original one was bad... Anyone have any clues?

[macster]

The 1200pF (C516) cap made the deck go way too fast. A 3kHz tape plays at 5kHz and the VF501 speed trimmer does not have enough range. I now believe the service manual is wrong. It won't be the first time a Nak service manual is wrong.

I'll have to source a new 2200pF cap and see if the original one was bad... Anyone have any clues?

PM the NAKDOC.

M~

[Nakdoc]

I wonder if someone put in a different pot? It should be 50k, and R512 should be 634k precision blue-orange-yellow-orange.
Studying it a bit more, C524 has probably been removed. It is (was) 1000pf and is in parallel with C516 1200 pf, so the last servicer added the two 1200+1000pf=2200pf.

[jazzgene]

I wonder if someone put in a different pot? It should be 50k, and R512 should be 634k precision blue-orange-yellow-orange.
Studying it a bit more, C524 has probably been removed. It is (was) 1000pf and is in parallel with C516 1200 pf, so the last servicer added the two 1200+1000pf=2200pf.

Thank you for your help. I checked:

1)The pot is 50k (actually measures 45k)
2)R512 looks original and is 634k. I did not measure it as I would have to take one leg off circuit to get accurate reading. Should I?
3)You are right, C524 is not there. Is there a consequence for using 1 2200pf cap instead of 2 caps 1000pf and 1200pf?

Regards.

[jazzgene]

I installed a 1000pF 1% cap for C524. The drift during playback is gone. It remains dead on through the course of tape play.

I am not sure whether this deck had a bad 2200pF cap or it really needs both C524 and C516. The service manual calls for a G tolerance for C516 and a standard J for C524. I don't think there should be any disadvantage by using one 2200pF cap instead of two caps to add up to 2200pF.

Anyway, thanks NakDoc.

[Nakdoc]

The G and J denote different types of caps. Both can be the same type...any low leakage stable cap is fine. They must have used two to simplify parts procurement. Isn't it nice when stuff works!

[faustus]

This has been an interesting thread. Congrats, jazzgene, on getting it sorted out. Great job supplying advice, Nakdoc!

[Scorpion8]

Great job supplying advice, Nakdoc!

*thumbsup* x5

[jazzgene]

The G and J denote different types of caps. Both can be the same type...any low leakage stable cap is fine. They must have used two to simplify parts procurement. Isn't it nice when stuff works!

I was curious to this difference. The G is 2% and the J, 5%. I heard from an experienced Nak tech that it is possible that Nakamichi put in the 2200pf cap to improve accuracy over having 2 caps.

I am tempted to replace the electrolytic caps on the DD motor pcb as well. The speed trimmer is also not resolving enough. I can't tweak the last 2hz with the trimmer to make it dead on. I suppose I'll have to live with the 0.067% speed difference from my Dragon.

[jazzgene]

This has been an interesting thread. Congrats, jazzgene, on getting it sorted out. Great job supplying advice, Nakdoc!

I am so happy my ZX-9 is singing beautiful. Thanks again Nakdoc for your advice.

[Nakdoc]

You add new meaning to "tweak". Try and find the spec for your speed meter before you agonize too much. Murphy's Law states that you will accidently crack the motor PCB while changing some perfectly fine electrolytics.
The 2% idea is interesting, but the whole idea of using a VR makes the actual capacitance tolerance unimportant.

[jazzgene]

You add new meaning to "tweak". Try and find the spec for your speed meter before you agonize too much. Murphy's Law states that you will accidently crack the motor PCB while changing some perfectly fine electrolytics.
The 2% idea is interesting, but the whole idea of using a VR makes the actual capacitance tolerance unimportant.

I use a Fluke frequency counter. I take the guessing out of the equation by first measuring the tone (3.0001 khz) and then record it with a Dragon and confirm Dragon plays back the tape at 3.0001 khz. I then check the ZX-9 and I can set it to 2.9998 or with the slightest tweak of the VR501, I get 3.0018 khz. These numbers are min/max average of the Fluke meter over 2 minutes. I used to just use tone F# (7) which in our day is 2960 hz. By this method, I don't need no meter as my ear will tune dead on without reference.

In the Nakamichi service manual, they are fine with +/- 0.5%! The horror. I make a living with my ear music performance wise and also mixing/mastering. I immediately hear a difference in pitch of 3 cents. 100 cents equals semitone.

I decided to let the DD motor pcb be. I've been visited by Murphy a few times! Just this past weekend, as I was measuring the w/f of my ZX-9, my T-100 gave up the ghost... The function knob now does not work and the unit remains in "speed w/f" mode regardless of the switch position.

[Nakdoc]

A semitone is 1% speed, and is generally considered as close to perfect pitch that people can hear. Your pitch sense is extrordinary! Good idea to use averaging...I had never thought of that. That is a good tip to those who set speed with counters.
Your T-100 simply needs a setscrew tightened in the knob.

[jazzgene]

A semitone is 1% speed, and is generally considered as close to perfect pitch that people can hear. Your pitch sense is extrordinary! Good idea to use averaging...I had never thought of that. That is a good tip to those who set speed with counters.
Your T-100 simply needs a setscrew tightened in the knob.

Hi Nakdoc,

I can assure you 1% speed is not semitone in pitch. It is 6%. 1% comes to 16.67 cents which is very easy to hear. I hear a pitch difference of 3 cents right away. Less than that, I feel it right away. Too sharp feels edgy and too flat feels nauseating. Pavoratti stopped a rehearsal because he specifically requested the orchestra to tune to A = 441. A violin player remained at A = 440 and it flew him into a rage!

I don't know where you got the definition of perfect pitch but by its very definition, it means you are able to instantly know the pitch name and replicate it upon request without any prior pitch reference. What you mention falls closer to regional pitch. Absolute pitch like mine is innate. My mother has it, I've had it since I first started piano at age 2 and both my younger brothers have it.

I suppose this is not too common in the real world but in the world of classical and jazz musicians, it is not too rare. I don't know how anyone can play jazz without absolute pitch or at a minimum, hyper relative pitch.

Regarding my T-100, it is not so simple. The knob is not loose. It clicks fine and mechanically feels sound. Perhaps inside the switch? I know this rotary switch is not easy to find.