Problems with microdrive. Bad ULA?

[llopis]

Hi everybody,

Now that I have a QL working, I'm making a new video for #QLvember on the QL and specifically on the microdrives. Much to my surprise, it looks like one of my microdrives isn't working correctly.

It was mdv1_ (like I've read in other threads that's the most common one to go). It would spin up and down no problem, but when I type dir mdv1_ it would spin up and very quickly give me "not found" (maybe 1-2 seconds tops). mdv2_ worked fine and would take significantly longer to return the dir information (maybe 5-7 seconds).

I did the usual checks: clean head, clean rollers, not moved out of place rollers... everything was fine.

I swapped the two units and the drive continues not working as mdv2_.

Does that mean it's likely the ULA on the microdrive itself? Can you think of any tests I could do to check (short of swapping the ULA with another drive). Now that I think about it, does the ZX Spectrum microdrive unit or ZX Interface 1 have the same ULA?

Thanks!

[Chr$]

Hi everybody,

Now that I have a QL working, I'm making a new video for #QLvember on the QL and specifically on the microdrives. Much to my surprise, it looks like one of my microdrives isn't working correctly.

It was mdv1_ (like I've read in other threads that's the most common one to go). It would spin up and down no problem, but when I type dir mdv1_ it would spin up and very quickly give me "not found" (maybe 1-2 seconds tops). mdv2_ worked fine and would take significantly longer to return the dir information (maybe 5-7 seconds).

I did the usual checks: clean head, clean rollers, not moved out of place rollers... everything was fine.

I swapped the two units and the drive continues not working as mdv2_.

Does that mean it's likely the ULA on the microdrive itself? Can you think of any tests I could do to check (short of swapping the ULA with another drive). Now that I think about it, does the ZX Spectrum microdrive unit or ZX Interface 1 have the same ULA?

Thanks!

There's some info here:

http://www.sinclairql.net/srv/qlsm4.html#s4d-f1

(I know you have an Oscilloscope!)

The ULA in the ZX Microdrive is the same.

[llopis]

There's some info here:

http://www.sinclairql.net/srv/qlsm4.html#s4d-f1

(I know you have an Oscilloscope!)

The ULA in the ZX Microdrive is the same.

Oh, great stuff. I hadn't found that in my initial searches. Looking at it now. Thanks Chris!

[Chr$]

When I send your parcel I'll include a ULA, may as well.

There are more technical people here that will probably have other ideas for you to try but I find that if an mdv doesn't work (and the basics are ok, inc the 7805 and the 2 electrolytic caps, if present) then it's nearly always the ULA that is faulty.

[llopis]

I've done some more diagnosing and it looks like the ULA is indeed faulty (following the instructions in the technical manual with the 100KHz signal and looking at the ULA signals directly).

I've seen mentions that replacing the ULA isn't trivial and I see that it's going to affect the read head in some way. I failed to find any specific information on this. Any particular tips for the easiest way to replace the ULA? (desoldering isn't the problem, I'm just concerned about the head and whether I need to remove it and somehow realign it afterwards).