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01-26-2020, 01:09 AM   #1
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Pentax MZ-2n mirror problem

I have a non working mirror on a Pentax MZ-5n but have not been able to find any obvious damage to the plastic gears or the cog on the motor shaft.

The motor simply seems to not have enough power to operate the gear train.

When the motor is removed from the gearbox it operates normally on 1.5v. There is no damage to the cog on the motor shaft and the motor can be stalled by holding the cog showing that the cog is not slipping on the shaft.

Is lack of power in the motor a known failure mode in this camera ?

Or could there be something else subtely wrong with gear box.

The gears look to be intact and clean and operate smoothly with the gearbox opened.

The gear alignment is also correct with the 0s in the green and yellow gears properly in line.

I will be very grateful for any advice regarding what could be the problem.

01-26-2020, 12:27 PM   #2
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It could be the motor has gone bad. Unfortunately it appears that the stock of replacement motors, at least in the US, have been exhausted years ago.

There is a repair place in Japan owned and run by former Pentax engineers and technicians which may be able to repair your camera.

The following thread:
My old-New MZ-S After Returning From Repair - PentaxForums.com

The question is if the expense of repairs worth it?
01-27-2020, 12:16 AM   #3
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Many thanks for your reply. Are you confirming that motors in the camera are known to have failed by going low power - but stll work (ie spin) OK when connected to an external 1.5v supply ? If this is the case I will open the motor to investigate.
01-29-2020, 01:20 AM   #4
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The company PR Camera Repair Inc has on their website a photo of the replacement motor that they used to stock for the MZ-5n which is marked as RF-N30CA-11150.

The Evercom website (who supply many small motors) lists a motor ERF-N30CA-11150 which has the same dimensions as the motor in the MZ-5n but has a voltage operating range of 2-5VDC and not the 1.5v that is mentioned for testing the motor in the MZ-5 service manual.

The original motor has the Mabuchi trade mark embossed next to the negative pole and they list an RF-N30CA-11150 in their documentation with the same specifications as the Evercom item.

The coil resistance of my motor is about 5 ohms which corresponds with the data given for the ERF-N30CA-11150 which gives a stall current of 0.79A which with a 5V supply would mean a coil resistance of 4 ohms.

Does anyone know whether the replacement motor that used to be supplied was indeed the RF-N30CA-11150 and if so whether the correct voltage to operate the motor is between 2 and 5 volts?

One way for me to properly answer this question would be to rebuild the camera (which is now in many pieces) and measure the voltage supplied to the motor when the shutter is fired.

I would like to avoid this so would be most grateful if anyone has deep knowledge as to the motor specification.

I now am getting fairly confident that the 1.5V mentioned in the service manual for the MZ-5 for operating the mirror motor does not apply to this camera.


Last edited by Geoffrey; 01-29-2020 at 11:58 PM. Reason: more information regarding my motor
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