The Sinclair QL Forum

tcat wrote: Straight edged ones are usually Iss#5, the ones on your pictures might be even pre-Iss#5 ones, as they do not have two mods applied, two diodes and one track cut from the rear of the head board assembly.

First of all, thank you very much for your useful information Tom.
Indeed they were installed on a iss5 board. Maybe you're talking about the same modifications described in the service manual? So should I apply these mods?

tcat wrote: It would interesting to see, what issue insignia you can read on your keyed edged drive?

The other units are marked ISS6, but unfortunately these straight-edged ones have no insigna

tcat wrote: Higher sector count during format may not possibly be too beneficial, as may result in poorer compatibility with other drives, or with the very same drive in the long run.

The strange thing is that these units are working better than the others (in my case). They can read or format cartridges (both original Psion and miscellaneous) otherwise unreadable or unformattable. Also they run tapes that are completely stuck with the other 4 drives.
Maybe it's only a matter of mechanics: my ISS6 units are electronically better but mechanically worn

tcat wrote: I have coded `mSpeed', a small tool indicating drive speed, that came underway when programming `mDoubler' mDump1,2 tape cloner/dumper/duplicator.

Interesting

Derek_Stewart wrote:
One thought occurred to me, is it possible to replace the MDV Tape reader with a more up to date reader?
Not sure what I mean here, just wondering if there is a replacement Tape reader or maybe something else.

You mean something like a "generic" tape reader or a compatible tape reader for Sinclair Microdrive cartridges? I'm afraid there is no replacement

The only device that copied the technical principles of Sinclair's Microdrives was the Rotronics Wafadrive for the Spectrum that came on the market at about the same time.
I have never owned one, but from tests it was bulky, even less reliable than original Microdrives and cartridge supply for those boxes dried out even sooner than Sinclair's.

Tobias

The same modifications described in the service manual

Yes, D22/D23 in series with R101/R102.

They can read or format cartridges (both original Psion and miscellaneous) otherwise unreadable or unformattable. Also they run tapes that are completely stuck with the other 4 drives

Not sure if the mod can influence the erase current, which is set by R25 on Iss#6 main boards. I therefore think both your Iss#5 drives may run a bit slower.

Can you swap tapes formatted on one Iss#5 drive, and still can read and write on the other? Tapes formatted on Iss#5, can you read and write on Iss#6?

Maybe it's only a matter of mechanics: my ISS6 units are electronically better but mechanically worn

I think that Iss#6 headboard just incorporated the mod, and had the motor power point closer to the motor. The headboard has also smaller vertical dimension, so you do not need stand off spacer above MDV2. (protection against MDV2 headboard being depressed by QL top lid case)

I could do the tests on two Iss#5 drives here, but I need to replace their r/w heads first (have only one spare head left), as they have faulty erase coils. Very common fault with MD units I have learnt. I could at least verify their speed.

EDIT I could also test removing the mod, while adjusting R25 on Iss#6, and see if it formats higher sector count.

Iss#5 headboard assembly sometimes have double head springs, making it a lot harder to push the cartridge to the slot, also resulting in scratching cartridge black plastics around cushion felt pad. (I usually remove one extra spring when the head needs replacing).

Tom

tcat wrote: Yes, D22/D23 in series with R101/R102.

I could try these modifications on one of the two units maybe

tcat wrote:Can you swap tapes formatted on one Iss#5 drive, and still can read and write on the other? Tapes formatted on Iss#5, can you read and write on Iss#6?

Tapes unreadable/unformattable with iss6 are usually red and formatted with iss5. Then the same tapes usually become readable and writable with Iss6.

tcat wrote: faulty erase coils. Very common fault with MD units I have learnt.

I did't know this. So if my units can erase we can say that erase colis are OK, I suppose.

tcat wrote: I could also test removing the mod, while adjusting R25 on Iss#6, and see if it formats higher sector count.

I think every test is welcome to the community

Hi,

Perhaps if you could measure R25 in your QL Iss#5 main board, it could tell us if R25 in your QL does not deviate from documented values in the Service Manual, this will then exclude that erase current is influencing higher sector you get. We could then concentrate on drive speed.

To tell whether an MD head will pass R/W test, you can just measure its coils.
2x 16R, 1x 96R.
On faulty erase coil you will measure around 750R (that's the diode).

Tom

My main boards are both ISS#6. Only two of my Microdrives are supposed to be ISS#5 (actually I have an iss5 QL, but it doesn't work).
Probably I don't have the skills to make such measurements, anyway I'll try.
Thanks for your suuggestions

Hi Cristian,

You may find Issue#6 board component layout helpful when locating R25 resistor, it is found in the middle column below modulator, to the left of MDV1 ribbon cables.

http://www.dilwyn.me.uk/docs/hardware/05.png

You can take a picture of its colour stripes that encode the resistance, or measure resistance by a multimeter(voltmeter) on a switched off machine. Since you have three boards, two functional, that is three measurements in all.

Let me know.

Tom

tcat wrote: You may find Issue#6 board component layout helpful when locating R25 resistor
You can take a picture of its colour stripes that encode the resistance

Thank you very much for your support Tom.
One thing is sure: all three motherboards have the same R25 resistor.
RED-GRAY-RED-GOLD = 2.8k Ohms 5%
But I may have misunderstood brown/red:
BROWN-GRAY-BROWN-GOLD = 180 Ohms 5%
So tomorrow I'll utilize a brighter lamp or try with a multimeter

The uncertain color was brown, indeed the multimeter indicates 180.
In one case I found a value of 184 but I presume this does't affect so much the microdrives.
So all 3 motherboards (iss#5 and #6) comply with the R25 specs of the service manual. I suppose it's a matter of microdrive speed and/or design.