Author Topic: 3.5" floppy head alignment  (Read 3491 times)

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Offline JonB

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3.5" floppy head alignment
« on: 16:00, 09 January 17 »

Well, now - here's a short tale of woe.

I have a 3.5" floppy drive connected to my PCW 9512 and I thought it was a bit noisy on seek, so I took it out for a service. One of the things I did was to clean the heads with a cotton bud. To do this, it was necessary to lift the top head somewhat, so I could get the cotton bud between both heads. So far, so good. I reassembled the PCW.

Then I found it would not boot any more (from the 3.5" disk). This drive looks to be a Locomotive supplied unit from the documentation that came with the machine. It has a small single sided adapter board between it and the PCW's drive cables with "PM37" and "(C) 94 SCA", which I assume is SCA Systems. It provides connectivity to drive's 34 way ribbon connector and (crucially, as I later found out) swaps the 5v and 12v lines as the PCW appears to have them the wrong way round. It looks to have a voltage regulator on it as well. The drive unit itself has no markings and as such cannot be easily identified.

I was pretty sure I had done something to the drive, but in order to rule out FDC damage, I connected it to a PCW8256 and it successfully formatted and wrote data to the disk, which I could then retrieve. Yet it is not able to read any of the 9512 (boot) disks.

This is a strong indication that the heads are misaligned (because the drive works but will only read files it wrote). Close examination of the drive's head carriage assembly shows that the spring that holds the top head down is slightly buckled and I think this is my fault for over lifting it. It is not a coiled spring; it's like a flat strip of thin steel, and the top head is mounted on the end of it. The damage is only slight but I'm sure it is the cause of the problem.

I don't have a head alignment diskette, but I do have a 'scope and a bit of patience. What things can I try to get it going again, other than random movement of the head adjustment parts? I was thinking I could detect the address marks on the top side of the disk by connecting the 'scope to the head..


Also, would any PC type drive work here? Looking at it, it appears to be HD because there is a HD detector switch. One problem is that the adapter board is designed with this particular type of drive in mind, so fitting another drive might prove tricky. I did have a spare floppy drive but I managed to fry it thanks to the Amstrad power coupling being back to front.. grr..
« Last Edit: 16:07, 09 January 17 by JonB »

Offline JonB

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Re: 3.5" floppy head alignment
« Reply #1 on: 18:16, 09 January 17 »
So, after much fiddling, I took the deformed spring out and straightened it, sort of, but the disk is still not aligned right.I did some hunting around and came across this page http://newsgroups.derkeiler.com/Archive/Comp/comp.os.msdos.misc/2006-06/msg00020.html


..which explains how to use Dave Dunfield's IMGDISK suite to check and align a disk. I have this software on an old PC I use to transfer stuff to CP/M boxes I also have, and following the instructions was able to get the drive going again.


Panic over...  :D

Offline GeoffB17

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Re: 3.5" floppy head alignment
« Reply #2 on: 18:24, 09 January 17 »
Hmm..


Firstly, when you attached the drive tp a PCW8256, and it 'worked', what do you mean?   I'd be surprised if it worked as it should, i.e. double sided 720k, as a PCW8256 wouldn't know about that.   Do you mean it just did a SSSD (i.e. 173k) format?   That would make sense.   Also, it you have damaged a spring connected with the heads, maybe the specific spring affects only the second side, hence side 1 worked OK  Anything on the head assembly, I think, would have little bearing on 'alignment' (although it's not impossible).   The matter of alignment is connected with the stepper motor, which needs to start at the right spot so that it can step through the tracks correctly.   Did you mess with the stepper motor?   You don't say?


I'd guess that the purpose of the spring is to maintain the correct pressure of the head against the disk surface.   If it's not maintaining enough pressure, then is may not work, but I don't know how critical that might be (as in +/- 10% might still be OK ??).   However, further messing with the spring may not risk affecting the alignment, which like I say, it controlled by the stepper motor.


I have a 3.5" drive (standard PC one) attached to my PCW8256, but as B:.   I've needed to fiddle the installation to get the drive to 'show' a ready signal (I use a tweaked cable).   I could have used any drive.   Some drives can be used easier (as in the drive can be adjusted to give a proper ready signal).


However, there is another 'problem', and I'm not sure about this.   With the 9512+, the purpose of the supplied (?) .FID file is to do something with the disk timing.   I don't really understand this.   Maybe it's something to do with the HD mode, maybe it applies to some HD drives and not others.   Anyway, the .FID code changes the timing.   I didn't need to do this with the HD drive I attached to my PCW8256, it just works at DSDD without any problem.   I'd assume other drives would also work.


Oh, regarding the voltage connectors, most current 3.5" drives are 5v only, and make no use of the 12v line.   The drive I have is external, and is powered from an external 5v adaptor (so as not to overstrain the power supply).   If your drive needs both voltages, it must be pretty old.   But yes, the connectors are the opposite way round to those used on a PC.


In summary:


Does your PCW use a FID file on loading?
Did you do anything with the stepper motor?
To clarify about the spring, please attach photo.
What was format done that 'worked'?
The wonderful Bryce may add to (or correct ?) some (or all) of the above!


Geoff

Offline GeoffB17

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Re: 3.5" floppy head alignment
« Reply #3 on: 18:27, 09 January 17 »
OK.


The instructions seem to relate to the stepper motor alignment, and not to the actual head (or a spring).   I assume you were able to adjust the stepper motor?


At least you've got it working again.


geoff

Offline JonB

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Re: 3.5" floppy head alignment
« Reply #4 on: 19:25, 09 January 17 »
It's an internal drive kit that was marketed by Locomotive Software, so it has a ready modification inbuilt (I suspect the jump wire I saw has something to do with it). On the head, there are two springs. One of them is this flexible bit of flat steel that allows the head to be lifted. It is acting much like a hinge. The other is a coiled spring that applies the downward force.


The problem was that, in buckling the flat spring, the top head was not sitting square on the disk surface, and I suspect this was the problem. To correct it I had to dismantle the head carriage, and there goes the alignment. I had to adjust both the stepper motor and top head alignment to get it going again (and it is still a bit fussy about reading other disks).


Let's talk about the FIDs on the other thread...


Offline robcfg

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Re: 3.5" floppy head alignment
« Reply #5 on: 21:07, 09 January 17 »
Could you take some pictures of that Locomotive kit?


Sent from my iPhone using Tapatalk

Offline Bryce

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Re: 3.5" floppy head alignment
« Reply #6 on: 22:38, 09 January 17 »
OK.


The instructions seem to relate to the stepper motor alignment, and not to the actual head (or a spring).   I assume you were able to adjust the stepper motor?


At least you've got it working again.


geoff

Stepper motor alignment is head alignment. The spring is just keeping the head at the right height above the surface of the disk.

Bryce.

Offline JonB

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Re: 3.5" floppy head alignment
« Reply #7 on: 10:30, 10 January 17 »
Hi Bryce


Normally, I'd agree with you, but on this drive you can loosen two screws on top of the head carriage mechanism and move the position of the flat spring and this moves the upper head relative to the lower head. It has a lot of adjustability, more than a track's worth of movement in any direction (forward, backwards, left, right) from the look of it. In order to get the thing working I needed a combination of stepper motor adjustment and upper head adjustment (and it is still a little bit flaky, but just about good enough for my purposes).


Cheers
JonB
« Last Edit: 10:32, 10 January 17 by JonB »

Offline Bryce

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Re: 3.5" floppy head alignment
« Reply #8 on: 11:58, 10 January 17 »
Wow, that's a bit of a wierd one and makes head alignment even more difficult. The heads should always be aligned relative to each other, so motor alignment is the correct one to use to move both heads at the same time. I'd try not to touch the other alignment, you may never get it back to the correct position if you are unlucky.

Bryce.

Offline JonB

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Re: 3.5" floppy head alignment
« Reply #9 on: 13:23, 10 January 17 »
I had to touch it, the flat spring was buckled, so I removed it for some "remedial action".


I think the buckled bit was causing the drive to not read stuff. The top head was visibly not square against the disk.

Offline Bryce

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Re: 3.5" floppy head alignment
« Reply #10 on: 13:33, 10 January 17 »
Is it really any different from a standard PC drive? Have you tried any other drives in the computer?

Bryce.

Offline JonB

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Re: 3.5" floppy head alignment
« Reply #11 on: 14:05, 10 January 17 »
The problem is the adapter board. It fits on this drive only. Having a power socket and data plug hard wired onto the PCB so as to plug into the corresponding connectors on the drive. It means that if a different drive is tried, the board won't fit it. I did try a PC drive (connecting the Amstrad power plug straight into the drive) and the drive got toasted. 12v into 5v is a bad idea! I didn't realise they were reversed.


So, one more 3.5" drive consigned to the bin.  :doh:

But there is no need to be concerned. I fixed the Locomotive supplied drive already... :)
« Last Edit: 14:07, 10 January 17 by JonB »

Offline Audronic

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Re: 3.5" floppy head alignment
« Reply #12 on: 14:56, 10 January 17 »
@JonB


Does the 3.5" floppy drive have a brand on it ?


It may be more cost effective to just replace the drive ??


Hoping that will help


Ray
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Offline JonB

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Re: 3.5" floppy head alignment
« Reply #13 on: 15:41, 10 January 17 »
No, just a serial number on the PCB.

Offline GeoffB17

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Re: 3.5" floppy head alignment
« Reply #14 on: 00:32, 11 January 17 »
Jon,


If it becomes essential, just take a couple of pics of the drive.   Back, top and bottom.  Pretty often, the different manufacturers are pretty distinct, and pretty similar between their different models.   I've got 3 or 4 drives here, different mfg, distincly different.


Geoff