Unable to format microdrives

[Bytesguy]

Hi Martyn, thanks for the tips! Lods of good info there I just checked again using mdv1 and the error seems to occur anywhere from 12 to 20 seconds. I'll run some more tests later on the other drives to see if this is consistent, but I don't recall having a very short (7 second) failed format.

It is really strange that even the known working spectrum microdrives also produce the same issue, so I am wondering if maybe mdv1 is a bit funky and that is having a knock on effect down the chain. Going to see if I can remove the internal drives tonight and just run some external ones, that would at least isolate the problem to the QL itself, or the internal drives causing issues I guess?

I am always a sucker for using the original formats if I can, microdrives are fascinating technology for the time

[martyn_hill]

You're very welcome!

When you come to try to isolate the internal units, bear in mind that simply removing a unit will block access to any further units down the chain - including any external Spectrum drives, due to the way that the COMMS OUT to COMMS IN chaining works.

Simply switching MDV#1 with MDV#2 (if you haven't already) would be a first step.

If you do want to remove a unit altogether, then it would be necessary to also bridge across the missing unit with a small wire connecting its COMMS IN (Pin 1 on the header) to COMMS OUT (Pin 2) - take care with that as the pin-out of those 14-pin DIL sockets is not entirely obvious! The next unit actually connected would then be recognised as (N-1) in the chain.

Charles Ingley supplies a neat device called the V-Map that does this drive re-assignment in a more active and intelligent manner - but the simple wire bridging is sufficient for your test.

Given the way that most of the signals are shared on the MDV bus (bar COMMS IN/OUT), one flaky unit impacting another perfectly good unit is absolutely possible...

Keep us posted!

[Bytesguy]

You're very welcome!

When you come to try to isolate the internal units, bear in mind that simply removing a unit will block access to any further units down the chain - including any external Spectrum drives, due to the way that the COMMS OUT to COMMS IN chaining works.

Simply switching MDV#1 with MDV#2 (if you haven't already) would be a first step.

If you do want to remove a unit altogether, then it would be necessary to also bridge across the missing unit with a small wire connecting its COMMS IN (Pin 1 on the header) to COMMS OUT (Pin 2) - take care with that as the pin-out of those 14-pin DIL sockets is not entirely obvious! The next unit actually connected would then be recognised as (N-1) in the chain.

Charles Ingley supplies a neat device called the V-Map that does this drive re-assignment in a more active and intelligent manner - but the simple wire bridging is sufficient for your test.

Given the way that most of the signals are shared on the MDV bus (bar COMMS IN/OUT), one flaky unit impacting another perfectly good unit is absolutely possible...

Keep us posted!

Thanks Martyn, even more good stuff there I was able to swap around the internal drives, but still have the same issue. I tried each one individually in position 1, no dice.

I checked some voltages and can see 9v (which is what I read is required for the erase head) is going to the mdv connector ok (in fact it's 9.8v, but that may be because it was unplugged so no load).

I just did the comms in/comms out chain so mdv1 pointed to an external drive (with both internal ones pulled out) and strangely the same issue!! I tried all 4 of my known working zx microdrives and a variety of re-felted carts, same issue every time.

It would seem like something is not happy on the motherboard, or maybe I have a buggy rom version?

I suppose at least this rules out faults in the microdrive units themselves?

[Chr$]

I suppose at least this rules out faults in the microdrive units themselves?

Possibly not, as I believe there are a lot of ZX Microdrives that don't work when connected to a QL. I managed to get one working first time, but there is a long thread here about people having all kinds of trouble getting a ZX drive to work as an external QL drive. I can't remember what the cause of the issue was, no doubt Martyn will know.

[Bytesguy]

So A bit more digging with the help of Rich from RWAP It looks like I have an issue 5 board and there seem to be a couple of resistors missing behind mdv1. I've uploaded the photos to this reply in case anyone is interested in taking a look. The serial number starts with D13 if that makes any difference!

[martyn_hill]

Hi again Bytesguy!

I was able to swap around the internal drives, but still have the same issue. I tried each one individually in position 1, no dice.

What rotten luck! Until you get at least one drive formatting at least one cartridge OK, it's tricky to find the root cause...

I checked some voltages and can see 9v (which is what I read is required for the erase head) is going to the mdv connector ok (in fact it's 9.8v, but that may be because it was unplugged so no load).

In fact, 9.5-10.5 is about right - it's the output from the QL PSU and only _nominally_ 9V. Even under normal load, it seems to stay around the high 9's... It also supplies the 9V motor, BTW...

It would seem like something is not happy on the motherboard, or maybe I have a buggy rom version?

To my mind, the motherboard itself has little to do with the _performance_ of the MDV units at this level - especially once you remove them from the case and avoid all the electrical noise.

But the ZX8302 on the other hand could be suspect here - the one common element across all the drives you've tried. Its quite possible to run a QL with a slightly dodgy 8302 in my experience, without realising it for a while...

Before getting too stuck-in, one easy thing to check is whether the standard mod is correctly attached between the 8302 and the -12V line - namely, a pair of 33kohm resistors soldered between pins 19/21 of the ULA and pin 1 of the 1488 (IC25). If they are not present at all, don't worry - they just 'help' and I've run drives without this mod perfectly well before. But if, say, one resistor is attached, but the other has come detached, then that would upset things.

If you can spare a few quid, Rich Mellor sells replacement 8302s and its always worth keeping a spare of the pluggable ICs to-hand when playing with suspect QL hardware...

As for a buggy ROM - I'm not aware of any ROM likely to be in circulation today that would cause this particular behaviour, but out of interest, which ROM is installed?

I suppose at least this rules out faults in the microdrive units themselves?

The jury's still out, but seems highly unlikely that ALL of them are somehow 'incompatible' with your QL...

...no doubt Martyn will know.

I'm afraid not, Chr$ - my experience is like yours - I've only tried one ZX drive on my QL and it worked perfectly well.

M.

[martyn_hill]

Hi again!

OK, just saw your latest post - you have a JM ROM set - should be fine with that.

The pair of 33k resistors look attached OK, but worth wiggling them to check.

I'll check the 'missing resistors' idea against the Service Manual and update again.

M.

[martyn_hill]

OK, so those apparently missing resistors behind the MDVs are probably actually fitted _underneath_ - its one of the more peculiar mods that were made to the earlier Iss5 boards.

This particular mod was to re-route a powerline away from the MDVs and the resistors are moved and re-attached to the relocated power line on the underside. The resistors have nothing to do with the MDVs themselves, IIRC.

However, if you're happy to remove the board form the case and take another photo, we can check...

[Bytesguy]

OK, so those apparently missing resistors behind the MDVs are probably actually fitted _underneath_ - its one of the more peculiar mods that were made to the earlier Iss5 boards.

This particular mod was to re-route a powerline away from the MDVs and the resistors are moved and re-attached to the relocated power line on the underside. The resistors have nothing to do with the MDVs themselves, IIRC.

However, if you're happy to remove the board form the case and take another photo, we can check...

Hi Martyn The resistors on the 8302 seem ok, everything seems firmly attached!

I have attached pics of the underside of the board, looks like you were right!

Rich is sending me a couple of known good QL formatted carts so that will enable me to test whether reading and writing is working or if it's just formatting that is an issue.

On balance of probability, it does seem like it's a problem with the QL itself, but you never know!

[martyn_hill]

Hi Bytesguy

Yes, those look about right and match the standard mods on my Iss5 board.

Whilst you're in touch with Rich, I'd very much recommend purchasing a spare 8302 - they are not expensive and it could well address the issue in one swell-foop

And if not, having the spare IC will come in handy eventually...

Aside from the 8302, the services offered by the motherboard itself to the MDVs are:
a) Power cct for the motor
b) Current for the LED
c) Current for the Erase head
- All the above are switched by COMMS OUT from the respective MDV ULA. And...
d) Switching for the Erase current (TR3) through diode D28 and resistor R25. Capacitor C46 filters the switching action a little.

Given that power is flowing and that multiple drive units exhibit the same format failure, item d above should be your next line of enquiry...

D28 simply jacks-up the voltage by c 1V at the emitter of TR3 as far as I can tell, reducing the overall voltage seen across the Erase head when TR3 is saturated ON - i.e. when the drive is active (COMMS OUT active), the WP switch activated _and_ the ERASE signal from the 8302 active. By 'WP switch activated', I mean to say that the WP tab or replacement sticky-tape is fully engaging the WP switch - actually DEactivating WP

TR3 could therefore be your culprit here - both Format and any Write activity will need TR3 to switch correctly.

It's the ubiquitous BC184 NPN type - easy and cheap enough to replace. There is only one Erase transistor for the entire MDV 'chain', so you might expect it to impact any and all units attached - as we are seeing here.

BTW - when using the ZX units with a QL, be mindful that the state of the WP tab/presence of sticky-tape will make NO difference to the QL's abiility to write to the cartridge! The QL will write and erase-away, blissfully unaware that it shouldn't