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Head Alignment +3 Disk Drive

 

If you have followed my guide on how to service the +3 disk dive and your drive will still not work reliably, there could also be a read/write head alignment problem if the +3 has been abused or dropped. This can be very tricky to fix without specialist equipment.  This guide sets out to show the enthusiastic amateur how to try and adjust the head alignment manually.

Be warned - a lot of time and patience can be exhausted on this repair! 

Symptoms of Head Alignment Problems

 There are various symptoms of dead alignment problems, the main ones being:

  • Cannot read known good commercial disks (you can hear the drive trying to read the disks as the head travels in and out across the full width of the disk).  The head will try two full spans of the disk before telling to "Insert tape and press PLAY".
  • Being able to format a disk without problem, but then when the CAT command is run you get "Track 0" or "Missing address mark" errors.
  • Being able to format and use disks on the machine, but not on any other +3.
  • Not being able to read disks formatted on someone else's +3.


Items and Tools Required

  • A medium cross head screwdriver (to remove the top of the Spectrum +3 case)
  • small cross head screwdriver
  • A small flat head screwdriver

 
Opening the Spectrum Case
Follow the instructions in the "Servicing the Sinclair ZX Spectrum Disk Drive" article to open the Spectrum case to expose the drive.  Leave the keyboard in the top case still connected, but laid open to the left out of the way.

Adjusting the Read/Write Head
The photographs shown here are of a drive which has been completely removed from the Spectrum for clarity of detail.  Your drive should be left in place in the Spectrum for easy testing.

Manual adjustment of the head alignment is performed by carefully adjusting a small alignment plate as shown in the photograph below:

Adjustment is performed by loosening a small screw on the alignment plate (this will be usually be very tight and perhaps held in place with a small blob of lacquer to prevent it coming loose).

There is a small notch in the adjustment plate enabling the plate to me moved by levering with a small flat screwdriver blade as shown in the photograph below:

Loosening the Adjustment Plate Screw
As shown below, loosen the plate securing screw slightly (just a fraction of a turn) - this may be quite hard and you may hear a crack as the lacquer breaks.

Adjusting the Head
Turn on the Spectrum and wait for the start menu to appear.  Now put a known good disk into the drive and press [ENTER].
If the head is out of alignment, the most common thing that will happen at this point is you will see the head move in and out twice, then stop with the message "Insert tape and press PLAY".

Now place a flat head screwdriver blade into the gap between the plate edge and the post on the disk caddy and gently move the adjustment plate a fraction to the left (in this picture) towards the worm drive motor (if the plate moves very easily, tighten up the screw a little more - you should be able to move the plate, but not too easily as it will not stay in place). 
See below:

Press the [BREAK] key twice to get back to the start menu, then press [ENTER} again.  If the adjustment was successful, then the head will find track 0, stop there and then load the program.  If you are lucky enough to get this right first time, then re-tighten the plate screw and check again.

More likely is that you will have adjusted slightly too far (if you go a long was too far you will hear the drive hit against the stop when it tries to move).  If so, now adjust back the other way, this time putting the screwdriver blade into the adjustment notch as below:

Keep trying until you get there - it can take a long time of trial and error.  If you are successful carefully tighten up the screw again and re-test.  If still OK, then a blob a nail varnish serves as a good replacement lacquer to stop the screw coming undone again.

Always service the drive first before attempting to align the heads - similar symptoms can be seen from a dirty head.

Good luck!

 


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