Microdrive Motor Adjustment

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Derek_Stewart
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Microdrive Motor Adjustment

Postby Derek_Stewart » Wed Sep 02, 2015 2:03 pm

Hi,

I read in the QL Service Manual that an Alignment Jig can be made to position the Microdrive Motor correctly.

But on the Microdrives I have from Issue 5 & 6 boards, the motor is secured by counter-sunk screws, which would secure the motor to the position of the counter-sunk holes.

I am not sure the purpose of the Jig detailed in the Service Manual


Regards,

Derek
Bloodnok
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Re: Microdrive Motor Adjustment

Postby Bloodnok » Thu Jul 14, 2016 2:02 am

Hi Derek,

The counter sunk screws can allow the motor to be set off center. They may appear to be self centering but with the amount of play existing there is no guarantee that tightening them up is going to center the motor. To test this I created a 3D model of the jig to the published design and printed a 3D version. I used 2mm round stock for the pegs. The result is a repeatable calibrated process which removes one variable among the several required to get the best performance out of these devices (along with head reseating, motor speed calibration, and pinch roller height setting).


tcat
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Re: Microdrive Motor Adjustment

Postby tcat » Fri Jul 29, 2016 7:42 pm

Hi,

I believe other variables are, stiffness of head springs and side spring.

EDIT
When the side spring is too weak, the tape running is not smooth and cartridge is audibly slightly noisy, with crunchy sounds.

Tomas
Last edited by tcat on Sat Aug 06, 2016 6:39 pm, edited 1 time in total.


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Re: Microdrive Motor Adjustment

Postby tcat » Fri Aug 05, 2016 8:20 pm

Hi Bloodnok,

I am curious about your experience with
head reseating
, as you mention among the variables.

I visually compared several MD units, and each has its head "tilted" in its own way, some facing slightly more up, other slightly more down, did not found two at the same level . The differences appear in fractions of millimeters, +/- 0.2-0.5 mm

Are these production tolerances, or is the head deliberately set to a specific position where it gets best quality signal from tape?

Many thanks
Tom


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Re: Microdrive Motor Adjustment

Postby Bloodnok » Sun Aug 07, 2016 6:32 am

Hi Tcat,

The QL service manual mentions the head position (see attached). I've followed the recommendation with good results. I wouldn't normally have changed the head position given its importance but needed to during the repair of several units I received as 'untested'. I've managed to swap head assemblies between units, and head boards, and reseated them all successfully.
Positioning the front two feet so that they meet the chassis makes sense as this is the reference plane. Along with ensuring that at least one of the rear feet touch as well doesn't give much room for misalignment. It would be interesting to hear if anyone has drives that don't follow this configuration (especially the position of the front two feet) and still provide good performance.
The reason for not all feet touching in some cases I assume is due to tolerances in the plastic molding. The azimuth is set by the screw on the right side of the assembly (and secured with loctite) and was most likely calibrated as part of the head manufacturing process meaning that later assembly was relatively straight forward without special tools.

Cheers,

Charles



Head position.jpg
QL Service manual - page D2


tcat
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Re: Microdrive Motor Adjustment

Postby tcat » Sun Aug 07, 2016 2:53 pm

Hi Charles,

Can you please help me in understanding, what is meant by rear and front feet, as I cannot see them?

R/W head is soldered through 6 pins, being a stereo head (I read somewhere), I assume one pair for each channel coil, plus erase coil.

There are also "tape guides" from either side of the head, guiding the tape slightly sideways, so it seems.

Head board with head assembly is fixed to the chassis using plastic rivets melted by heat, as it seems.

Many thanks so far.

Tomas


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Re: Microdrive Motor Adjustment

Postby Bloodnok » Sun Aug 07, 2016 11:03 pm

Hi Tomas,

Youre correct about the head - two channels and erase. The tape is half the width of audio cassette tape so it will be no coincidence that the head dimensions are the same as a stereo head. The head itself may have different electrical characteristics due to the different frequencies involved but I haven't looked into that so can only speculate.

As part of each head mount side plate there is a cutout on the lower side that creates two small 'feet' 1.9mm long (see attached photo).
Looking further into this, due to the way the azimuth is set by the right hand plate, it follows that most heads will only have three feet touching at once (two front and one rear). Once the head is seated correctly the tape guides will do the rest (being exactly the same width as the tape as far as I can tell).

Hope this helps,

Charles

Microdrive head assembly.JPG
Microdrive head assembly


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Re: Microdrive Motor Adjustment

Postby tcat » Mon Aug 08, 2016 8:18 am

Hi Charles,

Now I see the feet, the front feet in the red circles, right?

I also wonder how you go about head re-seating, this would involve melting away two plastic rivets, holding the head in two mounting holes?

Many thanks so far.
Tomas


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Re: Microdrive Motor Adjustment

Postby Bloodnok » Mon Aug 08, 2016 9:51 pm

Hi Tomas,

Reseating is only needed if the head is out of alignment due to the head board screws being loosened for some reason (replacing the ULA usually). If not, then only a confirmation that the two front feet and at least one of the two rear feet are touching the chassis is required. Otherwise the factory setting will be OK and the drive likely has other problems.
So no need to touch the plastic head posts unless the the chassis is beyond repair and the head needs to be salvaged and used in another drive. I wouldn't recommend it unless you like a challenge and the drives are otherwise a lost cause.

Cheers,

Charles


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Re: Microdrive Motor Adjustment

Postby tcat » Tue Aug 09, 2016 7:55 am

Hi Charles,

Thank you for explaining.

I have MD units, one with the head is slightly tilted up, and two front feet (red circled ones) not touching the chassis, the rear ones (close to head PCB board) do both touch though.

Some other MD units head slightly tilted down, two front feet touching.

Some other MD units head almost level, all four feet touching.

Read circled feet are REALLY meant as the FRONT ones, as when the head is up, it's face is up, so the feet right underneath might be also a bit lifted up?

Tape guides seemed 4-point welded to the head, and they do not seem aligned with the head in all cases I have seen so far.

I also do not understand the azimuth, is it a magnetic Norh-South orientation, or setting tape guiding slightly askew?

Thank you a lot for bearing with me.

Tomas



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