Servicing the Amstrad CPC6128 Disk Drive

The built-in disk drive of the Amstrad CPC6128 is a fairly robust (if non-standard) 3” system which is still very reliable some 30+ years on. However, if you purchase or acquire a 6128 which has not been maintained it is very likely that the drive will not work.

The problem is usually a perished drive belt, and/or dirty read/write head, and/or dried out lubrication of the worm drive which positions the head.
More than likely it will be all three!

This article sets out to guide the complete novice through servicing the drive and getting it back into full operation.

Items and Tools Required

  • Cross head screwdriver
  • Brush to clean out the dust and spiders
  • Long nosed tweezers (or similar)
  • Small pointed pliers (makes life easier)
  • Cleaning buds / swabs
  • Head cleaning fluid
  • New drive Belt
  • Vaseline or other light grease

These are recommendations, other similar tools will do – only the proper belt is essential.  Full service kits including cleaning tools, solution and belt are available from the shop.

Opening the CPC6128 Case
Work on a table or workbench with plenty of space and good lighting. Lay a cloth over the table to protect it (if your partner is watching) and then place the CPC face up on the cloth.


Firstly, remove the two small screws on the right of the drive housing on the right hand side of the CPC case (don’t lose them, they are difficult to find these days)! 

Now turn the CPC over so it is face down.

There are now six screws to remove from the base. On some models there is a 7th screw (marked) – if this screw is present, it is longer than the others – make sure it goes back in the same hole.

Carefully turn the CPC over again holding the top and bottom together to prevent them from falling apart.

Now, gently lift the top with both hands for about an inch, then carefully turn the top over from right to left and lay the top down on its keys at the side of the base.

Take care not to damage the keyboard ribbon which is connected to the motherboard at the left side.

The disk drive will now be fully exposed at the right hand end of the base case.

Removing the Disk Drive
The disk drive is held in place by two screws fixing it to two mounting posts. Remove these and move the earthing wire attached to the nearest post to one side.

Loosen the ribbon cable from the plastic cable tie hook on the base of the computer, then lift the drive and very carefully disconnect the flat 26 pin ribbon connector and the power supply lead from the rear.

Have patience and take care – if you pull too hard on the ribbon cable you will bend the pins or pull the connector from the cable itself (or both if you really go for it).

Servicing the Drive
Various types of drive were installed in the CPC6128, the most common being the EME-155. The EME-150A and the EME-156 were also used and the pictures used in this guide show all three at various stages of repair to try and make sure that the type you have will be covered.
Servicing instructions are the same for each drive type, but the motor leads and the screws securing the drive controller board (the drive base) to the drive itself may vary in their position and number. Also, some drives make use of a write protect pin (the drives shown in this guide do not) - the EME-156 is the most common.  Losing this pin during servicing has caused many people problems over the years – more of that later!

Keeping the disk slot towards you, turn the drive over to give access to the base.

Remove the two (or more) brass screws (take care not to lose any washers) securing the controller board to the drive noting the type and position (they can be different).

At the power and ribbon connector end of the drive controller board, you will find two or three sets of wires from the drive and stepper motors connected to the controller board (on other drive models, these may be at either side of the drive controller board).

Carefully and gently pull these with your fingers, moving gently from side to side until the the connectors come free of their sockets. You may need to ease them out a little with the pliers first so you can get a good grip on them.  Don't pull on the wires too hard with the pliers though - you will damage them.

Removing the board connectors is not essential, but it does give you a little more room to lift the controller card to allow space to remove the drive belt.

Replacing the Belt
With the drive entrance furthest away from you, you should now be able to lift and slide back the controller board towards you slightly (to release the LED from the from drive fascia) and then lift the controller board upwards an inch or so to reveal the drive belt.

Don’t turn the drive over with the controller board loose or you will lose the write-protect pin if one is fitted.

What you see now may vary.
If you are lucky the old belt will still be in one piece and you will be able to lift it off the brass capstan of the drive motor and the main pulley with the tweezers – the drive capstan (small brass pulley wheel) may be on the left or the right, depending on the drive model.  

If you’re not so lucky, the belt will have broken and be wrapped around the capstan.

If this is so, it is a little more difficult to remove and it will almost certainly leave a sticky black residue on the capstan itself.

Be diligent - this residue must be removed as it will cause the new belt to slip, or even come off during operation.

Any belt residues will alo cause the new belt to age very quickly.

The best way to clean off the residue is to apply a few drops of head cleaning solution to a cotton bud (or similar) and rub the capstan, turning it continually with your fingers until the entire residue has been removed.

 You may need to carefully scrape off any stubborn bits of belt with a small flat blade screwdriver. Be gentle though so as not to damage the soft brass.

Don’t skimp on this cleaning operation even though it’s difficult – it is very important.

When clean, allow the capstan to dry for a minute or two..

Now make sure that all bits of the old belt and any residues have been removed from the main pulley wheel.

They tend not to stick to the plastic wheel as badly as they do to the capstan, but they are much more difficult to see and are easily missed.

As with the capstan, you may need to use the small screwdriver again to make sure that no bits are left.

Finish off by cleaning the the wheel with a cotton bud soaked in head cleaning fluid.

If you have purchased one of our belt cleaning kits, the long wooden cotton bud sticks are for cleaning the large wheel.

Fitting the New Belt
To fit the new belt use the tweezers to place the belt over the large pulley first, then finish by stretching it carefully over the capstan.
Ensure that the belt fits snugly over both capstan and pulley and that is not twisted.

It is essential to use the correct belt.
I have had many drives sent to me for repair which have been fitted with belts which are too small. Some have even been fitted with elastic bands. Belts which are the wrong size either slip if too big, or damage the motor bearings if too small.  This damage can happen very quickly on drives which are 35 years old or more.

Be very wary of belts offered on eBay - only use sellers that you know and trust.  If they don't sell a wide stock of other retro computer items, it's likely that they won't have the technical knowledge to size a belt correctly - most now have to be specially made.

Now replace the drive controller board, ensuring that the LED fits back into its recess at the front of the drive and fix in place again with the brass screws.

Reconnect the leads from drive motor and the stepper motor to the connectors on the drive controller board.

Belt replacement is now complete.

Cleaning the Read/write Head
Turn the drive over again so that the controller board is downwards with the front fascia plate nearest to you.
You will see a black plastic bar next to the stepper motor drive worm with a felt pad on its tip. Lift this gently backwards (it is held in place under slight pressure by a small spring) and the read/write head will be exposed.

Clean read / write head with a pointed swab moistened with head cleaning fluid and then allow to dry. Check that there are no bits of cotton from the cleaning swab left on the head.

All that needs to be done now is to add a little grease (Vaseline is great) to the stepper motor drive worm drive and the service is complete.

On some disk drives (the EME-150A), the worm drive is smaller and is mounted in the top left of the drive.

The photograph to the left shows a drop of oil being applied to the worm drive of an EME-150A.

Re-Assembly
Re-fixing of the drive back into and re-assembly of the CPC6128 is the reverse of the removal and disassembly (after giving the inside of the 6128 a good clean of course).

Reconnect the Ribbon Data and Power Leads
An important point to remember during re-assembly is to make sure that the ribbon cable is connected to the disk drive the correct way around. The red (or sometimes blue) coloured wire at one edge of the ribbon cable has to be connected to pin 1 of the connector block. Pin 1 is next to the power connector (see photograph to the right).

Also ensure that the connector block is fitted squarely over all of the pins at the rear of the drive - it is easy to miss a row of pins at one end, or even a whole row - check from above and below the drive to make sure all pins are in the block.

Write-protect Pin
If you find one of these tiny silver pins on your work surface at the end of the service (shown here below one of the +3 case screws so you can get a feel for its small size), then your CPC6128 has an EME-156 drive.  You turned the drive over whilst the controller board was loose and the pin has fallen out. The drive won’t work properly without it (won’t save data to the disk), so you will need to open it up again to refit it (assuming it hasn't been eaten by a pet or a vacuum cleaner).

The pin fits into a small recess just in front of and to the left of the drive belt capstan (viewed from the front of the drive). See the photograph to the right - the recess can take some finding!

Most drives used in CPC6128 detect a write protected disk by using a light beam and sensor, and don’t make use of these mechanical pins – but you never know what you will find until you open up you machine – be careful and watch out for the pin!

If all is now well, you can re-assemble the 6128 - don't forget to refit the keyboard membrane tails (if you removed the top half of the machine) and the LED lead.

If the pin is missing, or you have lost it during the service, then spares are available here.

Drive Still Won’t Work?
If after following this service guide carefully your drive will still not work, then drop me an email with the symptoms and I will try to help.

It may need re-alignment of the read/write heads or it may have a stepper motor problem, both of which need specialist equipment to fix.

 
!

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