Two QLs One Microdrive.. different results.

[Spirantho]

Hi everybody,

I'm puzzled.

I have two QLs. My own personal one, an Issue 5.
Also my office QL which is to be used for testing things; this is an Issue 6.

A microdrive unit will work in my own QL. It will read, and format happily and reliably.
The same unit when put in my office QL will only format about 5% of the time.

The same unit in my own QL will load Lost Pharaoh (for example) with no problem.
Put it in to my office QL, and it'll eventually load the title screen (or 95% of it, sometimes), and then give a Bad or Changed Medium error.

I have another microdrive which usually formats perfectly in my test QL.

So from what I can see, my microdrive units are good (they work well on my own QL). My test QL also works (it can read and format, but is unreliable). I have tried a few microdrive ULAs - same fault. I have already changed all the electrolytic capacitors.

I have tried:
1) Swapping the ZX8302 (and resistors)
2) Wiring up to C40 instead of the serial chip for the -12V line (which doesn't have huge ripple anyway).
3) Wiring up the data outputs from the microdrive ULA directly to the ZX8302

No matter what I do, my Issue 6 just won't stop suffering from intermittent data loss. It can't be the IC socket for the ZX8302 as I wired up the data directly to it. -12V is at -12.33V. The 9V input line for the regulator on the microdrive unit is the same on both machines (looks like a sawtooth wave, but the +5V regulated output is fine).

Does anybody please have any suggestions before I pull out what's left of my hair?

Thanks.

[RWAP]

Have you tried the microdrive unit in mdv2 (you will still need one in mdv1 to give the electrical chain to access mdv2) ?

It could be one of the two Transistors on the motherboard TR6 / TR7 - there is one for each microdrive unit...

[Spirantho]

I know my mdv2_ does exactly the same on my test QL. I have tried using a different drive in mdv2_ but not this current one.. I can try it. TR6 and TR7 are for the comms line, though - I don't think that would affect the data output. That said, it's worth a try, I suppose.... but I'm not confident.
But thanks for the tip - you never know.

[RWAP]

I think it was Tony Firshman who suggested TR6 or TR7 - or is it in the service manual.... ?

[tcat]

Hi,

Rather belatedly, I found this interesting post.

On first reading I initially thought, there must be a difference between MD unit Iss#5 coming from Iss#5 QL and MD unit Iss#6.

I checked the wiring diagram of both MD Units Iss#5,6, they appear the same, visually they only differ in Headboard PCB, they are cut in different ways. MD Iss#6 Headboard has insignia Iss#6, I think, next to the left mounting screw.

MD units may perhaps differ in R/W heads and ULA versions, also I noticed on the QL Main Boards Issue 6, there are two pull down resistors R107/108 33K wired to ULA DATA1/2 pins and -12V, on Issue 5 there are wired differently as R102/103.

So what makes the MD unit performing well in one QL, and not performing well in the other?

Tomas

[Outsoft]

Very strange..

The issue 6 unit it the Samsung made?

Or in the Samsung QL the Unit and the ULA are different too?