Servicing the Sinclair ZX Spectrum +2 Cassette Drive

The built-in cassette mechanism of the Spectrum +2 is a fairly robust system which is still very reliable some 30+ years on. However, if you purchase or acquire a Spectrum +2 which has not been maintained it is likely that the cassette loading performance will be unreliable.

Fortunately, the problem is usually down to a worn/kinked drive belt, and/or dirty read/write head, and/or incorrect head alignment (azimuth). Often it may be all three!

There were two main models of the Spectrum +2 (plus a few minor revisions).

The first on the scene was the grey model which was the first Spectrum produced by Amstrad. Apart from the added cassette mechanism, it was virtually identical internally to the genuine Sinclair Spectrum 128.

The second model released was the black Spectrum +2A. This was a major revision and the main board was completely different and ran on through the +2B and +3 models (the +3 had the disk drive rather than the cassette of course).

However, for the purposes of this guide, the cassette mechanisms were very similar on all models and the servicing is the same. The guide sets out to guide the complete novice through servicing the mechanism on any model of spectrum to improve loading and saving performance. All photographs used are from the black +2A model.

The earlier Spectrum +2 had a smaller belt as part of its drive mechanism and replacement of this is covered at the end of the article.

Items and Tools Required

  • Cross head screwdriver
  • Brush to clean out the dust and spiders
  • Long nosed tweezers (or similar)
  • Head cleaning chamois stick
  • Head cleaning fluid
  • New drive Belt (available from the shop here).
  • Jeweller’s cross head screwdriver

These are recommendations, other similar tools will do – only the proper belt is essential.

Remove Screws
Firstly, remove the six screws from the base of Spectrum case – don’t lose them, they are difficult to find these days!  

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

Now, gently lift the top from the right hand end until you start to feel some resistance – this will be the cassette power & LED wire which will stop you lifting the top case any further.

Reach inside the case and carefully pull off the lead from its connector on the motherboard - this will free the case top which should now be lifted open fully, in an arc from the right hand end from right to left.

Be careful not to damage the keyboard ribbon which is connected to the motherboard at the left side.

Lay the top case face down at the left side of the base – it is not necessary to remove the keyboard ribbon connectors.

The cassette unit which is housed in the top case will now be fully exposed.

Servicing the Cassette Mechanism
Give the innards a good (but gentle) brush out (holding the nozzle of a vacuum cleaner over the case as you brush helps take the dust and debris away), try and remove all fluff etc from the pulleys, keys and sensors. Light grease was used to lubricate the pulleys, so you may need to wipe them carefully if fluff and dust is stuck to the wheels.

If you turn the large pulley wheel the drive belt passes over, the belt will move – one of the most common problems is a kink in the belt where it has sat stationary over the small capstan motor pulley whilst in storage for many years – you will see this clearly.

Replacing the Main Drive Belt
Remove the old drive belt with the tweezers.
Now remove the new belt from its pack and open out removing any twists which may have been introduced when it was packaged.

Carefully fit the new belt making sure it is fitted straight and fits snugly with no kinks or twists. If you move the large pulley, the belt should move smoothly.

It is essential to use the correct belt – I have had +2s sent to me for repair which has been fitted with belts which are too small, and some even bodged up with a tight elastic band. Usually it is then too late for repair as the 25 year old drive bearings have been ruined by the excess pressure exerted by the non-standard belt.

Replacing the smaller belt on the Spectrum +2 grey model
The earlier Spectrum +2 had a smaller belt as part of its drive mechanism. This belt is pretty robust and doesn't do as much work as the main drive belt, so it rarely needs to be changed. However, if your +2 has a particularly slack small belt, or you suspect that it is slipping, I can supply a replacement either on its own, or as part off a belt kit (available from the shop).

The small belt is a little more tricky to remove - using the tweezers, lift it from the small upper black pulley wheel first.

It can then be gently pulled out from beneath the large pulley wheel from the side, taking care to guide the belt through the small gap beneath the large pulley and the spring-loaded peg beneath it (see photograph left).

This peg is part of the "pause" mechanism which becomes active when the "pause" key is pressed down. It can itself can be a cause of poor loading performance as can catch on the aluminium base of the large pulley wheel causing it to slow down. This problem can usually be heard when loading data from cassettes.

There is also a small spring which forms part of the peg mechanism.
 It is possible to lubricate the spring and peg with the careful application of WD40 or other very light oil applied as a tiny amount on the tip of a small precision screwdriver, or similar.  This  usually frees up the travel of the peg and cures the problem.

The case can now be re-assembled (remember to refit the power/LED lead), again taking care not to damage the keyboard membrane tails. Replace all of the case screws – be very careful not to over tighten them - the posts the screws attach to are easy to break.

Cleaning the Recording Heads
Open the cassette door and press the [Play] key – the play/recording heads will move out and lock.

Add a few drops of head cleaning fluid to a chamois cleaning stick or cotton bud and rub both of the heads thoroughly to remove any iron oxide deposits.

Press the [Off] key and leave a minute for the alcohol to dry.

It is possible buy special head cleaning cassettes, but I find these are not particularly good at cleaning off oxide deposits which have sat there on the heads for years. They are fine however for regular maintenance cleaning following a service.

Checking the Head Alignment (azimuth)
The azimuth angle can be checked accurately with one of the bespoke kits to do this, but these are hard to find now (keep an eye on the Sales pages in the Sinclair section of the website, I have them occasionally).

A quick method is to adjust the head angle as a tape is starting to load. You will need the +2 connected up and turned on to do this and a tape which you know to be good.

Make sure the tape is re-wound to the start and press the [Play] key to load the game as you would normally.

Now press the [Pause] key and insert the cross-head jeweller’s screwdriver into the adjusting hole.

Press the [Pause] key again to re-start the tape.

When the loading border appears, move the screwdriver both clockwise and anti-clockwise until you see the "clearest" loading border on the screen. What you are aiming to see is the red bars and the blue bars in the loading border to be the same size during the long loading tone (not the short beep), and also for the bars to be stationary on the screen - that is not moving up or down. This is best case scenario and I appreciate that this is not possible in the real world after all this time, but aim as close as you can to this target.

You may have to repeat this quite a few times (you will have to remove the screwdriver to rewind the tape; it will only go in when the tape is playing) to get the best result.

This method is a little rough and ready, but effective with a bit of practise. Indeed, you may not need to adjust the azimuth, often just cleaning the heads and changing the belt makes all the difference.

Program Won't Load At All?
Another quite common problem is for a program not to load at all, often with no red/blue flashing of the screen border when the play key is pressed, no yellow/blue loading border and no loading sounds.

If your machine suffers from this problem, try pressing down with your thumb at the bottom left of the cassette door when you are trying to load a game, or sharply bang the computer against the table top. Usually you will hear the loading sounds again (sometimes very briefly). The pressure, or shock of the tap makes the electrical contact again.

This is usually caused by a "dry" solder joint.

The standard of soldering on assembled items like the cassette on these machines was variable to say the least, and at the point where the leads from the play head meet the cassette drive controller board, the solder is a dull grey colour, rather than the shiny metallic colour it should be. Poor solder technique using insufficient flux often causes this "oxidation" effect and over time, the joint breaks down and electrical contact is lost.

Re-making the solder joints very often cures the problem completely.

To do this, add a little flux with a fine children's paint brush to the grey solder blob, then hold the tip of a soldering iron against the poor joint. The solder will melt fairly quickly - take away the iron and the solder will set again, usually repairing the joint. Remake the joints for both the red and white leads as shown in the photograph.

Crackling interference
A static-like, noisy crackle heard through the TV speaker during loading is a similar issue to the dry joint problem described above.

In this case, the dry-joint issue is still there, but the joint hasn't broken down completely. However, it is still usually enough to badly impair loading performance. Again, try pressing down on the case again around the cassette unit whilst loading - the crackle may stop, or more likely get worse.

The cure is the same, BUT, the sound may be coming from other solder joints on the cassette controller board. The "crackle" problem seems to be more of an issue on the +2A boards rather than the +2 boards - possibly because the +2A, has more soldered cable joints.

If you have this problem, re-make the joints shown ringed in red on the photograph to the left.


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