Realigning an Amstrad 3" 720K floppy drive

I recently received this Email from Chris Wathen, and with his permission reproduce it here.If you've never tried this exercise it's a great test of patience and perseverance so plenty of time is needed. There are several versions of the drive but Chris's method will provide useful tips whichever version is worked on. I particularly liked the idea of using a chart fixed to the stepper motor. There are two sizes of motor so you may need to modify the size of the chart. The screws securing the motor are often very tight. I use a small watchmakers type screwdriver gripped in a locking wrench. The small motor has a tiny connector board attached which is sometimes close to a screw head and can easily be damaged, so take care .

Hi Ron,

I've succeeded in re-aligning a double-headed 720K drive! It's not a 100% perfect alignment, as I can no longer read any cheap 'white label' disks, nor can I re-format many of them either, but all good quality disks, as well as the original system disks (which must surely be a pretty good test of a re-alignment) work perfectly.

So, the beginner's guide to re-aligning an Amstrad 3" drive with nothing other than a screwdriver, a piece of paper and a system disk. This discussion is focused on re-aligning a PCW9512's A: drive. Obviously the same re-alignment techniques can be used if you're re-aligning other drives, but your testing procedures will be different.

If, like me, the need for a re-alignment was brought about by removing the board and a few attached components without realising that one of the attached components was a precision-aligned sensor which when out of place renders the drive incapable of reading anything other than disks it has formatted itself (not that I could even do that, because having the drive out of alignment meant that I couldn't boot my system either), the first thing you need to do is get the sensor back in place. Getting it exactly in the right place is a 1 in a million chance, but as a very rough guide, you need the top edge of the little board it is mounted on to be just below the top of the bump that keeps the top edge of the board in place (and I do mean JUST below, as in less than a millimetre below).

Reconnect the drive and insert your Locoscript master disk (the master disk is going to provide you with a more accurate alignment than a copy). If you've been unbelievably lucky with the sensor, your drive will work perfectly. Job over.

If you've been very lucky, some of the horizontal lines will start to appear, then the drive won't be able to find the rest of the tracks and will give up or if you've been reasonably lucky, the full white screen which you get at switch-on will be replaced with the one with the black border around it, but none of the horizontal lines appear and then the system gives up. If one of these happens, then you're not too far out with your sensor alignment and it shouldn't be too hard to get the stepper motor in place.

If, like me, you never get past the full white screen, then you've still got a lot of work left to do with the stepper motor.

The next stage (or the first stage if, unlike me, you didn't remove the sensor and so haven't started yet) is to re-align the stepper motor.

To aid doing this, it helps to make a little chart so you can see how far you have moved the motor (this is where the piece of paper comes in). The best way to do this is in a CAD package, draw a circle 25mm in diameter, and draw 10 equidistant lines out from the radius (so that they are 36 degrees apart). Stick this onto the back of your stepper motor. Then, make a mark on the top of the casing that the stepper motor is screwed to so you can align the two. Loosen the two screws on the back of the drive that hold the stepper motor on. You may want to take them right out and scrape all the varnish off the motor and the washers so that it will turn more easily. Replace the screws so that there is a little resistance offered, but not so much that it becomes hard to turn the motor.

Switch on and, using the Locoscript master disk once again, rotate the motor. As you rotate it, press hard onto the shaft. If you just turn it without pressing and then find a perfect alignment, it will be lost as soon as you tighten the screws because this will push the motor onto the shaft which will move the heads a bit, taking your drive out of the alignment again. And until those screws are done up tight again, DON'T TAKE THE PRESSURE OFF, not for one second.

If the drive was finding something (i.e. some of the horizontal lines were appearing, or even just the screen with the black border but nothing else) then the drive is no more than one track out of alignment, so the motor will not need to be turned more than one position in either direction. Turn it VERY slowly (so that you take about 30 seconds to move through one position) - the pushing onto the shaft helps with this. If you reach the next position on the chart and nothing happens, move it back to the original position and then turn it the other way. As soon as the horizontal lines appear, hold still and see if Locoscript can load. If the drive starts to struggle to find things, it needs to be turned a FRACTION more. The amount needed is so small that you won't feel it. Just apply a firm turning force to the motor, but not so much that you are consciously moving it, you want to feel like you're firmly TRYING to turn the motor, but you need a bit more pressure to actually turn it. It's hard to describe in words, you'll know what I mean when you do it for yourself.

When the full white screen appears again and the main loading of Locoscript starts, reset your machine (it helps to have a second person on hand to do this) and see if all the lines appear without any movement of the motor. You need to keep tweaking the position of the motor until all the lines appear quickly without the drive struggling. When you've got to this stage, allow Locoscript to continue loading. Ensure that it goes all the way to the disk manager screen without any problems. Now do those screws up as tight as you can without damaging the heads, and don't let off on the pressure until you've done this. Give it one more test run to make sure that it can load Locoscript without you holding onto the motor.

If you didn't have any response from the drive, then your heads could be anywhere. Rotate the motor onto each position on the chart until you get some sort of response from it. You should do this slowly, but not that slowly (you don't need to take any more than a couple of seconds to rotate through each section). When you reach the constraints of the cable, go back the other way. Once you've got a response from the drive, carry out the fine adjustment as detailed above. So, now you can load Locoscript. I don't know whether it is just an anomaly with my disks, but while my machine was fine with Locoscript, it couldn't boot CP/M (although it could read the disk in the Locoscript disk manager). In an act of frustration, I pushed the whole head assembly towards the back of the drive, hard. Surprisingly enough, that act of violence sorted the problem. If you have problems booting CP/M (from the master disk that is, always align your drives with the master disks), give it a try.

In all likelihood, you still haven't got a 100% accurate alignment, but it's as good as you're going to get without the proper equipment that was used to align the drive in the first place. My drive is now fine with the master disks and other good quality branded disks (Maxell, Panasonic, Amsoft etc.) However, it can no longer read any of white label disks, and it could only re-format a handful of them. So, if you're using a drive that's been realigned in this way, stick to using branded disks in it.

As I've no idea how long this alignment is going to hold out, I'm planning to install a 3 1/2" drive, copy all my CF2 disks onto 3 1/2" ones, and abandon 3" drives altogether. It might be an idea to do this aswell, as you don't want to risk having data stuck on CF2's that you can't get to because your drive is screwed. --- Chris.

C.WATHEN@SOFTHOME.NET