Microdrive Motor Adjustment

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tcat
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Re: Microdrive Motor Adjustment

Postby tcat » Sat Nov 05, 2016 6:41 pm

Hi Tobias,

Thank you for the ebay tips, perhaps MD heads are not that common after all, or were common only in the UK. QL MD head has three coils (2x read, 1x erase), while audio device heads have typically two coils and erase coil is then found in an erase head mounted separately.

So I am just thinking, what kind of audio devices from the 80's used same type of heads as those found in QL MDs.

Perhaps I might be also wrong and Sinclair had specific build to order heads?

Tomas


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tofro
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Re: Microdrive Motor Adjustment

Postby tofro » Sat Nov 05, 2016 7:23 pm

tcat wrote:Perhaps I might be also wrong and Sinclair had specific build to order heads?

Tomas


Tomas,

I'd really be astonished if Sinclair would have used specific heads for the MDs. This would absolutely not fit with their normal "design for cheap components" attitude. The Service manual says:

7.3.2 Data is recorded on two tracks using a standard stereo cassette head arrangement and is written in bytes, one byte to one track and the next byte to the other track.


(Id does, unfortunately also say that the heads are the only parts of a Microdrive that are not replacable. (My guess is they were mounted in the factory using a special jig to get the alignment right that wouldn't be easy to reproduce).

So I'd assume that also means "standard stereo cassette heads". MC cassette drives did use two-track heads for stereo record and play as well as single-track heads for erase.


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janbredenbeek
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Re: Microdrive Motor Adjustment

Postby janbredenbeek » Sat Nov 05, 2016 10:29 pm

tofro wrote:
I'd really be astonished if Sinclair would have used specific heads for the MDs. This would absolutely not fit with their normal "design for cheap components" attitude. The Service manual says:

7.3.2 Data is recorded on two tracks using a standard stereo cassette head arrangement and is written in bytes, one byte to one track and the next byte to the other track.


(Id does, unfortunately also say that the heads are the only parts of a Microdrive that are not replacable. (My guess is they were mounted in the factory using a special jig to get the alignment right that wouldn't be easy to reproduce).

So I'd assume that also means "standard stereo cassette heads". MC cassette drives did use two-track heads for stereo record and play as well as single-track heads for erase.

MC tapes are much wider than MD tapes, I guess about twice as wide. Also, MC cassettes have an A and B side since the sound track occupies only half of the tape width (with stereo, you have 4 tracks).
If you look at the heads of the MD drive, you see that they have tape guides on both sides, while ordinary cassette heads have guides on only one side. This is so that azimuth may be adjusted, which won't be possible with guides on both sides. I guess MD heads don't need azimuth adjustments as the signal recorded is digital and flat frequency response is not an issue as long as the 0s and 1s are discernible.
So the MD heads are certainly not standard MC heads, though the track width may be the same as MC tapes (you can record twice as much on two tracks, though with analog signals you run into crosstalk issues).

later, Jan.


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Re: Microdrive Motor Adjustment

Postby Bloodnok » Tue Nov 15, 2016 11:00 pm

In response to request in a previous post - here's a higher resolution image of the microdrive motor adjustment jig....

Motor-location-jig.jpg
Motor adjustment jig


Charles


tcat
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Re: Microdrive Motor Adjustment

Postby tcat » Fri Jan 13, 2017 10:27 am

Hi,

Thanks to All, I am making some progress with MD units. Here is almost complete MD disassembly of an old unit, that was not performing well. All it's components functional providing spares to other units to fix here.

I was surprised to see two `head springs' while I thought only one is needed?
QL-MD_unit_disassembly.JPG
an hour's work with soldering iron and suction pump



Tomas
Last edited by tcat on Fri Jan 13, 2017 11:01 am, edited 1 time in total.


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Derek_Stewart
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Re: Microdrive Motor Adjustment

Postby Derek_Stewart » Fri Jan 13, 2017 10:37 am

Hi Tomas,

Looks like you have done alot of work there.

With regards to the Motor Alignment Jig, how does that work, as the QL Service Manual does not indicate how the jig should be used.

The motor seems to secured on the microdrive mounting in countersunk screw locations, fixing the motor positions. Is the jig to locate the position of the motor securing location holes.


Regards,

Derek
tcat
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Re: Microdrive Motor Adjustment

Postby tcat » Fri Jan 13, 2017 10:57 am

Hi Derek,

I am not too confident of my findings yet, just having the idea that `jig' fixes the right angular distance between motor axle and the R/W head face. This dimension is most sensitive to get cartridge white roller properly engaged by the motor rubber roller.

EDIT
I guess precision of some (0.1 .. 0.2 mm), will not be guaranteed just by counter sunk screws, only if there were position fixing `pegs' right on the motor chassis, similar to ones found on the `jig' itself, but that would be more costly. It should be also noted, that motor and jig fixing holes are placed at an angle, possibly for this purpose.

Not sure I am close but I will try to draw an illustrative chart.

Tomas
Last edited by tcat on Mon Jan 16, 2017 11:29 am, edited 1 time in total.


Cristian
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Re: Microdrive Motor Adjustment

Postby Cristian » Fri Jan 13, 2017 8:27 pm

tcat wrote:QL-MD_unit_disassembly.JPG

Tomas, this image is simply spectacular :D


tcat
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Re: Microdrive Motor Adjustment

Postby tcat » Tue Jan 17, 2017 3:29 pm

Hi,

On Microdrive headboard two electrolytic capacitors are found. These seem very solid ITT make, could they dry up in years, if so what values you would recommend for replacement?

QL-MD_hdb.jpg
Headboard assembly with elyt capacitors


The Service Manual gives these values:
C9/C10 - 0.47uF / 35V
C11/C12 - 0.22uF / 35V

They seem smoothing capacitors around 7805 / 5V regulator, but polarity is strangely given as LT-FT, BK-FT. Left-Front? Back-Front?

EDIT 18-Jan'17
Another thought, the cap values are small and seem replaceable with ceramics. I wonder why ceramics was not fitted in prime production, back in the days?

Tomas


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Re: Microdrive Motor Adjustment

Postby Dave » Thu Apr 20, 2017 9:31 pm

Labeled like caps or resistors, packaged like diodes, screenprint on one says cap, soooo I'm going to sit on the fence!



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