QL MicroDrive electrolytic caps

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keyboardjunkie
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QL MicroDrive electrolytic caps

Postby keyboardjunkie » Wed Jun 09, 2021 11:52 am

Hi all,

Does anyone have a good source of the very small electrolytic caps (C10/C12) on the MDV2 back board? I mean in terms of the physical size, not value :-)

Thanks in advance,

Mark.


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Re: QL MicroDrive electrolytic caps

Postby Dave » Wed Jun 09, 2021 4:53 pm

C9/11 and C10/12 don't conflict with anything as I recall. As long as they're shorter than the 7805 itself, there shouldn't be any mechanical problems.

For everyone else:

C9/10 are a .47uF electrolytic
C10/12 are a .22uF in UK/EU designs and a .47uF on a couple of my Samsung US QLs.


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Re: QL MicroDrive electrolytic caps

Postby tofro » Wed Jun 09, 2021 5:00 pm

And, more generally:

QLs don't normally suffer from bad capacitors (At least I've never seen one that had).

Exchanging them is a purely cosmetic activity, IMHO.


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Re: QL MicroDrive electrolytic caps

Postby keyboardjunkie » Wed Jun 09, 2021 5:32 pm

Ahhh - ok, I was under the impression that it was good practice to replace those caps if the MDV was misbehaving.

I've got a QL that has an MDV2 that won't read / write / format anything. It just spins forever. Carts can be read/written/formatted in MDV1 just fine. Checked all the voltages (5v was down at 4.7v so replaced the 7805 and now it's back up at 5.01v). Replaced the ULA too - same issue. Changed the 2 ribbons - same issue. Now looking at TR4/5/6/7 and associated diodes as possible culprits..

Anyone got any other insight that I should check first?

Thanks for any help!

Mark.


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Re: QL MicroDrive electrolytic caps

Postby tofro » Wed Jun 09, 2021 5:36 pm

Mdv heads are known to degrade or break over time - But before you're opening that can of worms, you probably try exchanging the caps first ;)


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Re: QL MicroDrive electrolytic caps

Postby Pr0f » Thu Jun 10, 2021 7:37 am

I thought those transistors were associated with the motor drive circuitry - so if your motor is spinning - does that not suggest they are working?


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Re: QL MicroDrive electrolytic caps

Postby Derek_Stewart » Thu Jun 10, 2021 8:49 am

Hi,

I would remove the capacitors from the Microdrive board and test the capacitance with an ESR meter, this should give an indication of the requirement to chnage the capacitors, same for the the other components, should be removed and tested off board.

Reading the QL Service manual on Microdrive faults, indicating the primary cause of read/write failure is usually mechanical problems, which maybe the Read/Write head is out of alignment or requires changing.

I am not sure how to test the Micrdrive head, but I guess there must be a way of doing this.


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Derek
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Re: QL MicroDrive electrolytic caps

Postby tofro » Thu Jun 10, 2021 9:14 am

mdv head replacement is a bit of a tricky thing. There doesn't seem to exist a current source for new (or NOS) mdv heads other than Sinclair Microdrives - And if you go that way, you can just as well do a complete unit replacement, normally. Not considering the hassle you might have to go through for aligning the replacement head.


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Re: QL MicroDrive electrolytic caps

Postby keyboardjunkie » Thu Jun 10, 2021 10:36 am

Hey all,

The reason for looking at the transistors/diodes is that the MDV2 motor 'sounds' like it's running slower than MDV1's motor. When spinning, it's much lower pitched (that's the only way I can describe it) - is that even a thing? I'm sure that the drives have to spin at the correct speed to work.

I guess I could check the voltage on MDV1's motor and compare that to MDV2?

Thanks,

Mark.


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Re: QL MicroDrive electrolytic caps

Postby Nasta » Thu Jun 10, 2021 1:41 pm

If I was replacing these caps, I would not bother with elecrolitic ones as there are film and foil caps available in practically the same footprint, for that capacitance value. The typical working voltage will be 50 or 63V. The advantage, although the price might be a bit higher (on the other hand you may not even be able to find standard electrolytic caps at less than 1uf in stock at most suppliers), the advantage is that for all intents and purposes they last forever in that application.
Wima nad Kemet are some typical manufacturers. You can see the 0.47u here (lead pitch is 5mm, so it will require some bending of the leads closer together but that should not be a problem)
https://www.tme.eu/hr/katalog/kondenzat ... 1437945%3B



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