Dear all,

I=B4m just trying to repair my NAK CR-4 but I can=B4t trace the failure.
I would be very happy, if someone could help me.

Symptom:
The reel motor stops working after some time. It seems that the
temperatur has an influence, since the tape works fine without housing.

During normal operation, the motor voltage (out1 - out2 of motordriver
LB1649) is around 2,5 Volts. In case of malfunctioning, the voltage
drops down to 2,0 Volts.


Now, the question is, which component forces the motordriver to reduce
the voltage? With respect to the LB1649... where could I find further
documentation? The official datasheet isn=B4t detailed enough.

I would be grateful for any advice...

Greetings from Germany,

Jens Kupich

On 3 Aug 2005 12:23:34 -0700, "Jens" put finger to
keyboard and composed:

I´m just trying to repair my NAK CR-4 but I can´t trace the failure.
I would be very happy, if someone could help me.

Symptom:
The reel motor stops working after some time. It seems that the
temperatur has an influence, since the tape works fine without housing.

During normal operation, the motor voltage (out1 - out2 of motordriver
LB1649) is around 2,5 Volts. In case of malfunctioning, the voltage
drops down to 2,0 Volts.


Now, the question is, which component forces the motordriver to reduce
the voltage? With respect to the LB1649... where could I find further
documentation? The official datasheet isn´t detailed enough.

The LB1649 appears to be just a dumb power amp. I'd be looking at the
speed feedback from the motor or from some encoder wheel. There may
also be some logic which detects motor current.


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

On Thu, 04 Aug 2005 08:07:49 +1000, Franc Zabkar
put finger to keyboard and composed:

On 3 Aug 2005 12:23:34 -0700, "Jens" put finger to
keyboard and composed:

I´m just trying to repair my NAK CR-4 but I can´t trace the failure.
I would be very happy, if someone could help me.

Symptom:
The reel motor stops working after some time. It seems that the
temperatur has an influence, since the tape works fine without housing.

During normal operation, the motor voltage (out1 - out2 of motordriver
LB1649) is around 2,5 Volts. In case of malfunctioning, the voltage
drops down to 2,0 Volts.


Now, the question is, which component forces the motordriver to reduce
the voltage? With respect to the LB1649... where could I find further
documentation? The official datasheet isn´t detailed enough.

The LB1649 appears to be just a dumb power amp. I'd be looking at the
speed feedback from the motor or from some encoder wheel. There may
also be some logic which detects motor current.

Oops, I just realised the problem is with the reel motor, not the
capstan motor. The reel motor does not appear to be speed controlled,
assuming it follows the datasheet example. If the IC inputs are OK,
then I'd suspect the IC or the motor itself.


- Franc Zabkar
--
Please remove one 's' from my address when replying by email.

Your problem is due to carbon build-up on the motor commutator. You just need to take it apart
& clean the carbon out, or replace the motor.

--
Stephen Sank, Owner & Ribbon Mic Restorer
Talking Dog Transducer Company
http://stephensank.com
5517 Carmelita Drive N.E.
Albuquerque, New Mexico [87111]
505-332-0336
Auth. Nakamichi & McIntosh servicer
Payments preferred through Paypal.com
"Jens" wrote in message
oups.com...
Dear all,

I´m just trying to repair my NAK CR-4 but I can´t trace the failure.
I would be very happy, if someone could help me.

Symptom:
The reel motor stops working after some time. It seems that the
temperatur has an influence, since the tape works fine without housing.

During normal operation, the motor voltage (out1 - out2 of motordriver
LB1649) is around 2,5 Volts. In case of malfunctioning, the voltage
drops down to 2,0 Volts.


Now, the question is, which component forces the motordriver to reduce
the voltage? With respect to the LB1649... where could I find further
documentation? The official datasheet isn´t detailed enough.

I would be grateful for any advice...

Greetings from Germany,

Jens Kupich

"Stephen Sank" wrote in message
...
Your problem is due to carbon build-up on the motor commutator. You just
need to take it apart
& clean the carbon out, or replace the motor.

--
Stephen Sank, Owner & Ribbon Mic Restorer
Talking Dog Transducer Company
http://stephensank.com
5517 Carmelita Drive N.E.
Albuquerque, New Mexico [87111]
505-332-0336
Auth. Nakamichi & McIntosh servicer
Payments preferred through Paypal.com
"Jens" wrote in message
oups.com...
Dear all,

I´m just trying to repair my NAK CR-4 but I can´t trace the failure.
I would be very happy, if someone could help me.

Symptom:
The reel motor stops working after some time. It seems that the
temperatur has an influence, since the tape works fine without housing.

During normal operation, the motor voltage (out1 - out2 of motordriver
LB1649) is around 2,5 Volts. In case of malfunctioning, the voltage
drops down to 2,0 Volts.


Now, the question is, which component forces the motordriver to reduce
the voltage? With respect to the LB1649... where could I find further
documentation? The official datasheet isn´t detailed enough.

I would be grateful for any advice...

Greetings from Germany,

Jens Kupich



I had an MR1 with a bad reel motor a while back. I was able to fix it by
unsoldering one terminal, and applying about 6 or 7 volts DC to the motor
and letting it run all night. Seems these type motors fail more from disuse.
Sure beat the heck out of trying to mechanically repair the motor. This of
course would not work on a motor with a shorted brush, but these types tend
to open up instead.

Mark Z.

Hi Franc,

If the IC inputs are OK, then I'd suspect the IC or the motor itself.

..=2E.that=B4s the question. The LB1649 has for each channel four inputs.
These are

IN1,IN2 direction
VCC power supply
VZ1 voltage adjustment for motor

The VCC and VZ1 have a direct affect on the voltage that is applied to
the motor through out1 and out2.
According to the service manual, I have checked the measuring points
related to these pins.
The result:

IN1 and IN2 (coming from =B5C) are perfect
VCC and VZ1 are different to reference values BUT both in case of
failure and normal operation. That means, even if the tape is working
correctly the measuring points have although wrong values. Must I
understand that ???

What I will do now is to replace the capacitors and transistors
involved in this circuit and, as recommended, to clean the motor,
whereby I doubt that the brushes are the failure cause.

Thank you for answering that fast... and if you still have a guess, I
really appreciate it.

Jens

Hi Stephen,

according to your address, you have an indepth experience in servicing
NAK VCRs. Please let me pose one more question to you:
The tape works fine, when the case is open and the electronic circuits
are cooled sufficiently. Isn=B4t that an indication that an electronic
component is overheating and causes the malfunctioning of the reel
motor? Couldn=B4t it be that e.g. a capacitor is depleted and affects
the Input values of the motor driver IC?

Best regards,

Jens

Another vote for replacing the reeling motor, or letting it run all night.
Replacement has never failed me in perhaps a dozen times in various Naks
suing this setup. Letting it run is iffy. However, I like to use Mark's
technique on the stroke engagement motors.

In article ,
Mark D. Zacharias wrote:

"Stephen Sank" wrote in message
...
Your problem is due to carbon build-up on the motor commutator. You just
need to take it apart
& clean the carbon out, or replace the motor.

(snip)

I had an MR1 with a bad reel motor a while back. I was able to fix it by
unsoldering one terminal, and applying about 6 or 7 volts DC to the motor
and letting it run all night. Seems these type motors fail more from disuse.
Sure beat the heck out of trying to mechanically repair the motor. This of
course would not work on a motor with a shorted brush, but these types tend
to open up instead.

Mark Z.

Hi,

I=B4ve applied 6.5 Volts to the reel motor and let it run the whole day.
Now, I could hear four tapes in series without any problems.

It seems the motor and not the driver was malfunctioning.

So thanks a lot to all people who helped me solving my problems.

Jens