Sinclair ZX Spectrum +2 Datacorder Belt Replacement

The grey +2's twin-belt cassette mechanism, seen with the top half of the case laid keys-down (photo: Spectrum for Everyone)

The Datacorder cassette deck built into the grey Sinclair ZX Spectrum +2 is driven by two rubber belts: a main belt round the flywheel and a smaller clutch belt. When they stretch or perish the tape speed wanders and the deck struggles to wind. Spectrum for Everyone notes that the mechanical parts come from cheap mono tape decks, so the work is that of an ordinary cassette recorder.

The black +2A and +2B use a different mechanism with a single belt.

Symptoms

• Playback speed varies noticeably, or the deck has difficulty fast-forwarding or rewinding a cassette: replace both belts.
• Speed still varies after new belts are fitted: the pause latch under the flywheel may be fouling it (see Pause latch below).

Faults that look similar:

• "R Tape loading error" with steady playback speed is a dirty head or wrong azimuth; see Sinclair ZX Spectrum +2 Datacorder Azimuth Adjustment.
• A constant hum or buzz on the sound is a grounding fault on the tape PCB; see the Sinclair ZX Spectrum +2 Troubleshooting Guide.

Safety

There is no mains voltage inside the +2: the mains transformer is in the external power pack. Unplug the power pack before opening the case.

Tools and parts

Grey +2 cassette mechanism parts (Amstrad)

Ref.	Part	Amstrad part no.
1	Erase head	170202
2	Record/play head	170201
3	Motor, 6 V DC	172027
4	Clutch belt	172028
5	Main belt	172029
6	Pinch roller	172030

• Replacement belts. Spectrum for Everyone points to DataServe Retro's belt kits, or to two CPC (Farnell) belts: a large belt that fits the main drive of both the grey +2 and the black +2A, and a smaller belt that only the grey +2 needs. CPC lists the large one, order code AVBELT107, as a square-section rubber belt of 70 mm internal diameter and 1.2 mm section, and links the small one as CPC order code AVBELT74.
• A screwdriver for the six case screws, and tweezers.
• Isopropyl alcohol and cotton buds for the head, capstan and pinch roller.
• Superglue, if the pause latch needs repairing.

Procedure

Opening the case

1. Unplug the power pack and any peripherals.
2. Remove the six screws holding the case together.
3. Separate the top and bottom halves, disconnecting the keyboard ribbons and the tape deck connector.
4. Lay the top half on the bench keys-down. The cassette mechanism is now in view.

Replacing the belts

Amstrad's exploded view: clutch belt (4), main belt (5) under the flywheel, motor (3) and pinch roller (6)

1. Lift the old belts off with tweezers. Note how they run before removing them; Amstrad's exploded view shows the main belt (5) under the flywheel and the clutch belt (4) beside the motor (3).
2. Fit the smaller (lower) belt first, then the large belt.
3. Check that neither belt is twisted.
4. While the deck is open, clean the tape head, capstan and pinch roller with isopropyl alcohol on a cotton bud.

Pause latch

The flywheel with the white pause-latch parts underneath (photo: Spectrum for Everyone)

Do this only if the speed still varies with new belts.

1. Turn the large flywheel with a finger and check whether it rubs on the white plastic latch of the pause mechanism below it.
2. The latch floats on a plastic pillar under a white "hat" that is a push fit on the pillar, with a spring inside. If the hat has cracked, the spring pushes the latch up against the flywheel.
3. Remove the small circlip on the top side of the mechanism, at the capstan.
4. Withdraw the flywheel from the underside of the mechanism. Keep the tiny washers, and the hat, spring and latch, safe.
5. Put a dab of superglue inside the hat, refit it with the spring and latch on the pillar, and hold it until the glue has set.
6. Refit the flywheel and the circlip, and check that the hat now clears the flywheel.

The circlip on the capstan that retains the flywheel, circled (photo: Spectrum for Everyone)

Reassembly

1. Reconnect the tape deck connector and the keyboard ribbons. Make sure the ribbons are fully inserted and not kinked.
2. Bring the halves together and refit the six screws.

Testing

1. Play a tape and listen: the pitch should be steady, without wavering.
2. Check that fast-forward and rewind run a cassette end to end without slowing.
3. Load a program. If the speed is now steady but loading still fails, clean the head and set the azimuth as described in Sinclair ZX Spectrum +2 Datacorder Azimuth Adjustment.

Revision notes

The grey +2 was built with two different tape PCBs, a UK board (Timex 377 211002) and a Taiwanese board (Z70501), with the same capacitor values but axial or radial parts. The belt work is the same on both. The black +2A and +2B have a single-belt mechanism and a third tape PCB.

Related pages

• Sinclair ZX Spectrum +2
• Sinclair ZX Spectrum +2 General Maintenance
• Sinclair ZX Spectrum +2 Troubleshooting Guide
• Sinclair ZX Spectrum +2 Capacitor Replacement Guide
• Sinclair ZX Spectrum +2 Datacorder Azimuth Adjustment
• Amstrad Spectrum +2 Service Manual