OTARI MTR-90 Capstan Motor Problem.

Stratech · 24th November 2003, 03:25 PM

Is there anyone out there that has experienced the same problem that I am having with an Otari MTR-90?
The machine was working fine until something spooky happened.
As soon as you turn on the power switch, the capstan motor spins at a slow rate, even before you load the servos. Upon FFor REW the motor wants to spin off the machine. I am getting 5 volts at the capstan motor at idle. I am getting 40 volts in FF or REW!!!!
I have another working machine that I have swapped all cards, motors, sensors etc. All boards have been replaced. all cable harnesses have been rung out. The power supply and transformer have also been swapped out. The cards from the bad machine have been installed in the good machine and all work OK.
I have spoken with the Otari tech department and they basically can't figure it out. At this point I am suspecting a mother board, which I have checked out to make sure a piece of tape or a razor blade is not shorting anything out.
If you guys and gals know of this problem, please let me know.
Thanks.

gyraf · 24th November 2003, 04:39 PM

This could be an error in the power-amplifier driving the capstan?

Have you included the power driver transistor assemblys (accessed from machine rear) in the card swapout experiment? This is the most likely source of errors at the capstan motor.

Jakob E.

Stratech · 24th November 2003, 05:19 PM

Yes, I have replaced that board too! However, I did some intensive testing at that location. The low voltage signals that the motor amp receives is OK for both reel motors, but I am getting 40 volts at the small connector that feeds that board. I performed a test by connecting the capstan motor feed to a reel motor feed on that board and the capstan was fine. As soon as I connected the low voltage feen from the capstan to one fo the reel motors, the reel motor was behaving like the capstan motor The problem occurs before the capstan signal hits that amp board. I traced the cables to the lower motherboard that houses the logic cards and all cables were OK. I even went as far as taking the logic motherboard out of the machine and rung all contact points. All was fine there too. This is voodoo at this point!!!

gyraf · 24th November 2003, 05:43 PM

Check voltage at the output of the capstan control pcb (pin18). Should be 0V at stop. Check offset and gain trimmers (TR1-2-3-4 and Vr5-6) for breakage around the output stage and IC10. Check voltage at negative feedback input (capstan control pcb pin20). Be sure to check the tacho disk - adjust it according to the manual if waveforms are wrong. Misadjustment of tacho can damage the capstan motor.

Jakob E.

Stratech · 24th November 2003, 05:56 PM

Hello Jakob, I've gone as far as replacing the cards and the motor.
I will perform the tests you have suggested.
Thank you for the info.
Charlie C

Jay Kahrs · 25th November 2003, 05:26 AM

Where in NJ are you? I know a pretty good tech if you need one who's based out of Westchester County, NY.

Stratech · 25th November 2003, 01:48 PM

I'm in Central Jersey. I have been repairing analog decks for around 25 years. This is one of those cases where you have done everything known to technical mankind and you are defeted by the laws of physics. The deck has been stripped down to a bare chasis and built up with known working parts and the problem still presists. What is the tech's info?
Thanks.
Charlie.

Stratech · 1st December 2003, 04:41 PM

Hello Jakob, I tried all of your recommendations and all is fine except that on pin 18 on the capstan card I am getting 6 volts in stop mode. I tried a different working card and the results were the same. What are the odds that the motherboard is at fault here?
Thanks
Charlie

gyraf · 2nd December 2003, 01:43 PM

There is three places this voltage could come from.

- The capstan controller board: We don't think the problem is caused here, as you tried another control card.

- The capstan Power Drive Assembley. This has two input diodes (to reduce backwards leakage?) in it's input. To ckeck if the error voltage comes "back" from the PDA, pull off the input connector to the capstan Power Drive Assembley card. If there's still an error voltage at the capstan driver card output, the error must be somewhere at:

- The interconnection - "Mother II" - board. Not at all funny to trace for errors.

Jakob E.

therz · 14th April 2008, 04:52 PM

What was the fix for the run away capstan?
Thanx .
T

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24th November 2003, 03:25 PM	#1
Stratech Gear Head Join Date: Nov 2003 Location: New Jersey Posts: 42	OTARI MTR-90 Capstan Motor Problem. Is there anyone out there that has experienced the same problem that I am having with an Otari MTR-90? The machine was working fine until something spooky happened. As soon as you turn on the power switch, the capstan motor spins at a slow rate, even before you load the servos. Upon FFor REW the motor wants to spin off the machine. I am getting 5 volts at the capstan motor at idle. I am getting 40 volts in FF or REW!!!! I have another working machine that I have swapped all cards, motors, sensors etc. All boards have been replaced. all cable harnesses have been rung out. The power supply and transformer have also been swapped out. The cards from the bad machine have been installed in the good machine and all work OK. I have spoken with the Otari tech department and they basically can't figure it out. At this point I am suspecting a mother board, which I have checked out to make sure a piece of tape or a razor blade is not shorting anything out. If you guys and gals know of this problem, please let me know. Thanks.

14th April 2008, 04:52 PM	#10
therz Gear interested Join Date: Apr 2008 Posts: 1	otari 90 capstan fix What was the fix for the run away capstan? Thanx . T

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24th November 2003, 04:39 PM	#2
gyraf Gear addict Join Date: Jun 2002 Location: Denmark Posts: 455	This could be an error in the power-amplifier driving the capstan? Have you included the power driver transistor assemblys (accessed from machine rear) in the card swapout experiment? This is the most likely source of errors at the capstan motor. Jakob E.

24th November 2003, 05:19 PM	#3
Stratech Gear Head Join Date: Nov 2003 Location: New Jersey Posts: 42	Yes, I have replaced that board too! However, I did some intensive testing at that location. The low voltage signals that the motor amp receives is OK for both reel motors, but I am getting 40 volts at the small connector that feeds that board. I performed a test by connecting the capstan motor feed to a reel motor feed on that board and the capstan was fine. As soon as I connected the low voltage feen from the capstan to one fo the reel motors, the reel motor was behaving like the capstan motor The problem occurs before the capstan signal hits that amp board. I traced the cables to the lower motherboard that houses the logic cards and all cables were OK. I even went as far as taking the logic motherboard out of the machine and rung all contact points. All was fine there too. This is voodoo at this point!!!

24th November 2003, 05:43 PM	#4
gyraf Gear addict Join Date: Jun 2002 Location: Denmark Posts: 455	Check voltage at the output of the capstan control pcb (pin18). Should be 0V at stop. Check offset and gain trimmers (TR1-2-3-4 and Vr5-6) for breakage around the output stage and IC10. Check voltage at negative feedback input (capstan control pcb pin20). Be sure to check the tacho disk - adjust it according to the manual if waveforms are wrong. Misadjustment of tacho can damage the capstan motor. Jakob E.

24th November 2003, 05:56 PM	#5
Stratech Gear Head Join Date: Nov 2003 Location: New Jersey Posts: 42	Hello Jakob, I've gone as far as replacing the cards and the motor. I will perform the tests you have suggested. Thank you for the info. Charlie C

25th November 2003, 01:48 PM	#7
Stratech Gear Head Join Date: Nov 2003 Location: New Jersey Posts: 42	I'm in Central Jersey. I have been repairing analog decks for around 25 years. This is one of those cases where you have done everything known to technical mankind and you are defeted by the laws of physics. The deck has been stripped down to a bare chasis and built up with known working parts and the problem still presists. What is the tech's info? Thanks. Charlie.

1st December 2003, 04:41 PM	#8
Stratech Gear Head Join Date: Nov 2003 Location: New Jersey Posts: 42	Hello Jakob, I tried all of your recommendations and all is fine except that on pin 18 on the capstan card I am getting 6 volts in stop mode. I tried a different working card and the results were the same. What are the odds that the motherboard is at fault here? Thanks Charlie

2nd December 2003, 01:43 PM	#9
gyraf Gear addict Join Date: Jun 2002 Location: Denmark Posts: 455	There is three places this voltage could come from. - The capstan controller board: We don't think the problem is caused here, as you tried another control card. - The capstan Power Drive Assembley. This has two input diodes (to reduce backwards leakage?) in it's input. To ckeck if the error voltage comes "back" from the PDA, pull off the input connector to the capstan Power Drive Assembley card. If there's still an error voltage at the capstan driver card output, the error must be somewhere at: - The interconnection - "Mother II" - board. Not at all funny to trace for errors. Jakob E.