External microdrive problem

[bwinkel67]

I recently got an external microdrive which seems to be a bit faulty. Does anyone know best way to debug one?

When hooked to my Spectrum via ZX Interface 1, it formats a microdrive cartridge anywhere from 2K to about 35K. I can even save and load a program. It's never consistent and mostly settles on between 15 and 20K. The same microdrive cartridge on the QL formats to about 216 sectors (108K).

When hooked to the QL it cannot read any cartridges and fails to format any -- presumably because on the QL the cartridge has to format to a minimum number of sectors. So the microdrive sort of works but something is faulty. I changed out the motor with a spare and that didn't change anything.

What would cause it to partially work but miss so many good sectors when formatting? Would a bad ULA cause that? Or is it something else? (bad capacitors, faulty voltage regulator, etcc...)

[dilwyn]

I've never known a ZX Spectrum external microdrive be able to format a QL cartridge. I think that Sinclair tweaked the speed of the QL drives - slightly higher sector count as a result. Probably the speed difference is more critical when formatting, but still allows QL to otherwise read and write to a working unit.
I also trust you are aware that when an external drive is attached to a QL, with standard cabling, the ZX microdrive attached to a QL ends up back to front, i.e. the cartridge slot faces away from you.
Before investigating the hardware side, I hope you've got some good re-felted cartridges to try, in case any older ones you have might be deteriorating.

[tofro]

Also: Give the head a thorough clean. Such a low number of sectors on the ZX Spectrum doesn't necessarily need to be a "real" hardware problem (or: It's rather unlikely it is). Apparently, the drive works in principle.

[bwinkel67]

Also: Give the head a thorough clean. Such a low number of sectors on the ZX Spectrum doesn't necessarily need to be a "real" hardware problem (or: It's rather unlikely it is). Apparently, the drive works in principle.

That's my first goto having wrangled with my QL microdrives for years. I still use them for fun so head cleaning (and sometimes a dab of oil on the motors) happens, especially whenever I get a "format failure" which sometimes fixing it.

Yeah, seems to be able to format and read/write, but sometimes it ends with 1k or even 0k and the same cartridge gives 108k on the QL, so something must be amiss.

I've never known a ZX Spectrum external microdrive be able to format a QL cartridge. I think that Sinclair tweaked the speed of the QL drives - slightly higher sector count as a result. Probably the speed difference is more critical when formatting, but still allows QL to otherwise read and write to a working unit.

Oh, I didn't realize that. I thought they were the same. I'm guessing speed is controlled by the ULA or circuitry on the main board? I ask since I swapped motors and the spare was from a QL drive.

I also trust you are aware that when an external drive is attached to a QL, with standard cabling, the ZX microdrive attached to a QL ends up back to front, i.e. the cartridge slot faces away from you.

Yup, it looked silly, but I just wanted to test it since it had so few sectors (well it showed it only in kilobytes) on the cartridge with the Spectrum.

Before investigating the hardware side, I hope you've got some good re-felted cartridges to try, in case any older ones you have might be deteriorating.

All have been refelted and read on the QL. I've found a certain felt salvaged from music cassette's has worked best for me on the QL. I didn't try a bunch of them for reading since I didn't know about the format issue. Will try that...but if the Spectrum's slight speed increase would take a cartridge down to less than 25% of its capacity that would be a shame.

There's got to be something else going on. I know the ZX Interface 1 works because the person from the Netherlands that sold it to me actually sent along a video showing it working (and has had good reviews from fellow Sinclair folks on the Facebook group -- he seems like a very enthusiastic Sinclair collector fixing them and re-selling them). There was corrosion on the edge connector, which I fixed. I'll check the rest of the parts for continuity, resistance, and proper voltages as a first pass. The ULA seems to do its job, so I don't think it's that.

[bwinkel67]

I think I've fixed my external microdrive. It still won't read/write a QL formatted cartridge, but it seems to work flawlessly on the Spectrum. I've gotten it to format as high as 86K, and supposedly it doesn't go much above that -- Andrew Penmell, in his "Master Your ZX Micrordrive" book, claimed the most he ever got was 92K.

I ended up refurbishing it via this Byte Delight set of instructions:

https://www.bytedelight.com/?page_id=1623

I also replaced the motor with a couple of different ones that I had lying around (I have a spare QL microdrive, and for some reason, an extra motor as well). The first replacement got me to 83K and it could read a directory listing when hooked to the QL, but no read/write of a file. I just replaced it with another motor that works even better. That got me up to 87K and I was able to fill most of the cartridge (all but 11K so far) without error. I need to hook this one to the QL to see if it can go further than just reading the directory listening.

Btw, the Spectrum has this weird feature where you poke 23791,N where N is the number of copies you want saved when you use the SAVE command. I did a couple of files with N being 75 and it worked (quick way to fill up a drive). Supposedly, you now have to delete each file 75 times to get rid of it. Not sure what it does if one of them gets corrupted...does it go to the next one? It doesn't show you the number of copies you have, it just appears as a single copy that won'd disappear when you use the ERASE command. Just a very odd feature.

[bwinkel67]

The other oddity is that the ZX Microdrive boards are different from the QL ones...I would have expected them to be the same. But the daughter board (i.e. base board) on the ZX drives controls the motor speed, whereas on the QL, that comes form the head circuit board.

[Bloodnok]

The other oddity is that the ZX Microdrive boards are different from the QL ones...I would have expected them to be the same. But the daughter board (i.e. base board) on the ZX drives controls the motor speed, whereas on the QL, that comes form the head circuit board.

Hi,

Have come a bit late to the discusion but thought I may clear up a few things.

Both the QL and ZX microdrives run at the same tape speed. The speed is controlled by a variable resistor in the motor housing.
The data rate on the QL is 10us per data bit while the ZX is 12us. The theoretical extra data capacity is consumed by additional information stored in the QL format and gives no additional usable data capacity to the user.
The QL imposes a format sector minimum of 200 (100K). Any cartridges that fail to achieve this fail format. In a rather cynical way, this allowed Sinclair to 'guarantee' a minimum cartridge capacity of 100K.
During development of the vDrive QL I modded the Minerva OS (as it conveniently has source code) rom to ignore the format limitation to aid my investigations.

Hopefully this helps.

Cheers,

Charlie

[tofro]

In fact, there are subtle differences between various ROM versions and what they accept as a "proper format". MG is probably the most picky one in that it asks for at least one bad sector on a cartridge and a minimum amount (200) of working ones. JS and Minerva don't enforce a bad sector, and earlier ROMs might even have the 200 sectors limit lowered (can't remember).

[Bloodnok]

In fact, there are subtle differences between various ROM versions and what they accept as a "proper format". MG is probably the most picky one in that it asks for at least one bad sector on a cartridge and a minimum amount (200) of working ones. JS and Minerva don't enforce a bad sector, and earlier ROMs might even have the 200 sectors limit lowered (can't remember).

Yes - the vDriveQL ensures that a sector is marked 'bad' for certain roms.

[bwinkel67]

Both the QL and ZX microdrives run at the same tape speed. The speed is controlled by a variable resistor in the motor housing.
The data rate on the QL is 10us per data bit while the ZX is 12us. The theoretical extra data capacity is consumed by additional information stored in the QL format and gives no additional usable data capacity to the user.

Does that mean that the ZX microdrive hooked to a QL should be able to format a cartridge in QL format?