Using ZX Microdrives on the QL

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Timbucus
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Re: Using ZX Microdrives on the QL

Postby Timbucus » Wed Apr 19, 2017 8:08 pm

Hi Tomas

The ratchet was to stop a loop forming when the cartridge was inserted - once it is it moves the little ratchet out the way - you can just about make out the toothed bottom in the photo and of course on the diagram from the service manual.

ratchet.jpg


I assumed the roller was damaged initially which is why I swapped in a ratchet one but, it almost seems to be made that way but, is very smooth and hard and it was strange the bump was in the middle - unless someone read on the net about turning it upside down without realising the implications of such bad damage being inverted - I wonder how many cartridges they destroyed before abandoning it.

Tim


tcat
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Re: Using ZX Microdrives on the QL

Postby tcat » Thu Apr 20, 2017 9:37 am

Hi Timbucus,

The drive still does not format on ZX?
You mentioned some elyts and polystyrene caps replacement, r/w head seems alright.

How can ULA influence formatting, as I always though it as two channel operational amplifier and signal FM merger for reading `0' and `1' from two tracks.

Tomas


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Re: Using ZX Microdrives on the QL

Postby tcat » Thu Apr 20, 2017 9:53 am

Hi Charlers,

This lead to the question of why the choice of values for R4/R5 on the ZX Microdrive. Out of all the combinations I tried the only one that failed on the QL was the very one which was chosen for the ZX. Why would that be? Be great if someone could confirm what I’ve found.


Could it have been a marketing decision to set this incompatibility on purpose, to increase demand for QL's, and planed QL external drive?

Tomas


Dave
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Re: Using ZX Microdrives on the QL

Postby Dave » Thu Apr 20, 2017 6:36 pm

This is my personal opinion:

No.

Sinclair was at the time developing and evolving products at a tremendous rate. Clive's philosophy was based around using cheap or marginal components and getting the best from them - keeping hardware simple and doing it in software. The QL was really the first diversion from that path.

He took an existing known good system and miniaturised and cost-reduced it to the bone. He could have done it using audio cassettes, but then he would have needed to use two motors or an interesting gear system to direct traction to the required cog to shuttle the tape back and forth. His love of elegance led him to the microdrive system.

As they developed the ZX Microdrive and put it on sale, they learned about real world problems like tape stretch and tape lube issues. They corrected these for the QL, then ICL developed the logic even further.

I don't think Sinclair had a plan for future capacity or speed increases. They were already following the razor blade model of selling the drives at cost then making money on the media. It was inherent to the design that you couldn't use longer tape media, so you'd have to replace the device and OS and maybe more besides for future upgrades.

And that, my friends, was a symptom of what killed Sinclair Research.


tcat
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Re: Using ZX Microdrives on the QL

Postby tcat » Thu Apr 20, 2017 7:34 pm

Dave,

Yes, now I believe so, too.
MD unit is very simple device, with only few components, compared to 80's taperecorder, must have been for a fraction of the cost.

`tape lube' caught my attention, what sort of liquid lubricant was used, I guess to minimise tape wear, also to prevent from jamming in the long run?

Can this lube be reapplied to old carts?

Tomas


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Re: Using ZX Microdrives on the QL

Postby Dave » Thu Apr 20, 2017 8:06 pm

Interestingly, the tape lube issue played out again in the late 90s with DAT and DV tapes...

Initially, they used a wet lube. It tended to migrate from the front to the back of the tape more than in reel to reel tapes because the back of the tape was rubbed over the front during spooling. Once on the back it would be quickly absorbed by the sponge, wiped off and dry out as exposed to outside air. This forced a move to a more expensive dry lubricant that would not dry out or transfer as easily.

The big problem happens when using a mix of wet- and dry-lube tapes in a single device. The dry lube mixes up with the wet lube oil, forming a paste. This would clog and dirty helical scan heads particularly. Not too big a problem on microdrives, but lumps of it could build up and cause a symptom very much like when microdrives eat their felt.

It's not really feasible to re-apply a wet lube. Dry lube is put on the tape by the tape manufacturer before it ever gets put into a product.


tcat
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Re: Using ZX Microdrives on the QL

Postby tcat » Thu Apr 20, 2017 8:28 pm

Hi,

Perhaps slightly off topic, QL MD's have two elyts of very small dimension compared to ZX MD's.
What would be drop-in replacement to them in QL, they seem very solid makes, unlike in ZX MD's, if it makes sense to replace them after years?

Tomas


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Re: Using ZX Microdrives on the QL

Postby Dave » Thu Apr 20, 2017 8:30 pm

elyts?


tcat
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Re: Using ZX Microdrives on the QL

Postby tcat » Thu Apr 20, 2017 8:37 pm

Well, they look like electrolytic capacitors to me. Small roundish black plastic case.
Circled in red, please see picture here.
viewtopic.php?f=2&t=1381&p=15749#p15749

Tomas


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Re: Using ZX Microdrives on the QL

Postby tcat » Fri Apr 21, 2017 11:13 am

Hi,

I have wished to know, what was the mass market 80's audio tape device, that used same combo r/w/e head as Sinclair also sourced for their MD units?

Was it a walkman, car radiotape? What make?
I can imagine the production must have gone in ten of thousands quantities.

Any trace of it in UK, posters, magazines, adverts?

Tomas



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