Using ZX Microdrives on the QL

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Derek_Stewart
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Re: Using ZX Microdrives on the QL

Postby Derek_Stewart » Tue Apr 18, 2017 4:05 pm

Dave wrote:While the PCBs are very different between the Speccy and QL the schematics are functionally identical. Unless the Speccy and QL devices use different ULAs, the resister values and possibly head resistances might be the only differences.

In theory, the Spectrum can support 8 microdrives, and the QL already having 2 could support 6 more.


Hi Dave,

I just wondered if the ZX Microdrive mechanism, i.e. the drive part, was replaced by a QL Microdrive, would this solve the situation. If so, then the ZX Microdrives could be updated to QL standards...

ANother question comes to mind, can QL Micrdrives work in ZX Microdrives attached to Interface 1?

Maybe need a IF1/MDV Tech Guide.


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Derek
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Re: Using ZX Microdrives on the QL

Postby Dave » Tue Apr 18, 2017 5:31 pm

Right now I am looking at the hidden major difference between the ZX microdrives and the QL microdrives.

One way they differ sharply is in the handling of the motor. On the ZX microdrive, it hard starts and on the QL it soft starts, getting to speed over a half second or so. This caused a lot of problems with physical media on the Spectrum - the tape would be stretched and fail quite quickly. I'm trying to find out if this soft start was controlled by the ULA or was managed by the addition of a large external cap or similar.

It would be quite trivial to design a small board to replace the connector board in the ZX microdrive housings. Then a donor QL microdrive and the board could make for proper connecting additional microdrives. Given the demand for them, it might be worth it to somebody to do them as they could be made at home from a 2-layer board.


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Re: Using ZX Microdrives on the QL

Postby Outsoft » Tue Apr 18, 2017 8:49 pm

Derek_Stewart wrote:
Dave wrote:While the PCBs are very different between the Speccy and QL the schematics are functionally identical. Unless the Speccy and QL devices use different ULAs, the resister values and possibly head resistances might be the only differences.

In theory, the Spectrum can support 8 microdrives, and the QL already having 2 could support 6 more.


Hi Dave,

I just wondered if the ZX Microdrive mechanism, i.e. the drive part, was replaced by a QL Microdrive, would this solve the situation. If so, then the ZX Microdrives could be updated to QL standards...

ANother question comes to mind, can QL Micrdrives work in ZX Microdrives attached to Interface 1?

Maybe need a IF1/MDV Tech Guide.


This ZX Microdrive that I have works perfectly on the IF1 and on the QL ;)


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Re: Using ZX Microdrives on the QL

Postby Timbucus » Tue Apr 18, 2017 8:57 pm

I seem to have spent almost all day on this issue and written about five draft posts... Long and short of it my long cable I had made had become intermittent from all the plugging and unplugging so most of my findings were less than useful or reliable...

Both my drives (03466) no stamped number just a sticker and (03-057044) seem to work fine on a QL to read/write and format. I have made no changes to 03-057044 but, 03466 had new C1/C2 ceramics (to replace the Polyesters) and replacement Electrolytics (just because it was not working) to get it going in the first place - it is definitely now the star performer though; so perhaps these devices dropping in tolerance are affecting the results?

E.g. Using the same cartridge QL_mdv1 (217/223), 034660 (231/234) and 03-057044 (211/219).

My third drive can be unreliable even on the Spectrum (04-083529) to format so it was probably not a fair test but it was opened up anyway. As I did not have 330ohm resistors handy I swapped R4/R5 for 2x220 which are well within the QL range documented on the original post. This did not help on the QL but, the drive still functions on the Spectrum to read prewritten cartridges it is no better at format. As my others work there is no point in trying the resistor mod. When I next pickup parts I will get some 330ohm and try again but, I fear the drive has other issues - any suggestions welcome!

My final drive (D02-02334 again only a sticker as its one of a pair I had in plain cardboard boxes with my original Interface 1) is dead (awaiting a new ULA be fitted) but it, and the two others I opened had the 150ohm/180ohm pair with a Gold 5% tolerance band. As XorA points out that could still get it to 189ohms (or higher in 80s devices) at the start of the QL area on the chart by Bloodnok. I may never repair this drive as its case now houses my IDE to SD board for my QUBIDE - and very neat it looks with only minimal non visible damage to the base to let the 40 pin cable exit to the right and the SD card in the drive slot. This is the most reliable "Microdrive" I have for the QL...

Tim


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Re: Using ZX Microdrives on the QL

Postby tcat » Wed Apr 19, 2017 9:02 am

Hi Timbuctus,

I am just curious.
Can you measure resistance on upper / lower / erase coils of the R/W head of the third drive 04-083529?

Tomas


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Re: Using ZX Microdrives on the QL

Postby Silvester » Wed Apr 19, 2017 9:18 am

Bloodnok wrote:I haven't been able to locate copies of the articles mentioned in QL Today or Quanta on the OPD drives - can anyone point me in the right direction?

If permission can be granted from Quanta I can scan article.


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Re: Using ZX Microdrives on the QL

Postby Dave » Wed Apr 19, 2017 6:37 pm

I think that would be covered under fair use.


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Re: Using ZX Microdrives on the QL

Postby Timbucus » Wed Apr 19, 2017 6:44 pm

The picture below shows where I took the measurements (in ohms) - I assume they are the correct positions as I don't have a head pinout.
04-083529 34660 Broken
Red = Erase = 90.8 85.8 87.6
Blue = Track 1? 14.6 13.7 14.3
Green = Track 2? 14.3 13.9 13.8

While looking again in detail I noticed that this has the mandatory mod 2.3(c) to add a 47nF Cap between pins 9&12 of IC1 (circled in yellow) - I added this to 34660 myself which I forgot to mention in my last post. All drives have the mandatory mod 2.3(a) slow start 22uF C7 fitted to reduce the effect that damages the tapes mentioned in a previous post.

Although this is a later serial number I swapped the roller for one with a ratchet tensioner (undoing mod 2.3(e)) from the faulty one as it came with the funny looking one in the inset (34660 has the ratchet...) - in actual fact the shaped roller was upside down to the photo and created a nice indent all around the test cartridge for me... so maybe it was faulty at manufacture or had a bad repair? (It was one I bought from e-bay).

Out of interest when I revert the ratchet roller to my faulty one the motor continues to spin and does not report "MD not present" on CAT but does do so on FORMAT which is why I suspect a fault on the ULA... The unusual roller just adds to its problems... Anybody got some spare rollers they can donate? Or suggest a suitable donor device / source?

By the way I also measured the (still original) resistors on 34660 and they show 153/182ohm so not as high as 5% would allow - and this works fine on a QL...

So apart from this drive being a bit unreliable for some reason it does seem similar to the star performer... (i.e. new caps, all mods etc) just no luck on a QL.

04-083529diode.jpg


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Re: Using ZX Microdrives on the QL

Postby Dave » Wed Apr 19, 2017 6:52 pm

That pinch roller is jacked!

Interesting to know that's how they implemented the soft start. It would be a highly recommended mod for all Spectrum drives, yeah :D


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Re: Using ZX Microdrives on the QL

Postby tcat » Wed Apr 19, 2017 7:00 pm

Hi Timbucus,

The erase coil gives good readings in my opinion (so do r/w coils), so this should not affect format r/w performance, I should think.
Ratchet tensioner caught my attention, amazing, I only heard about them, is it a piece of metal spring clutching against the rubber roller, to slow it down on start/stops?

Tomas



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