Sinclair ZX Spectrum +2 General Maintenance

The grey ZX Spectrum +2. The Datacorder on the right is the part most likely to need attention on any surviving machine.

This guide covers preventive maintenance for the grey Sinclair ZX Spectrum +2 (boards Z70500 Issue 3 and Z70700 Issue 1). It does not apply to the black +2A/+2B, which are different machines built on the +3 platform.

The maintenance priorities are the Datacorder (belts, head, grounding), the fragile Amstrad PCB, the keyboard membrane and the 7805 regulator and heatsink.

Safety

There are no mains voltages inside the computer — it runs from an external supply and the highest rail on the board is +12 V. The mains transformer is inside the external PSU. Observe normal anti-static precautions for the Z80A, ULA, AY-3-8912A and RAM.

Note: the grey +2 uses a 2.1 mm barrel jack, while the later +2A/+2B use a 6-pin DIN. Their power supplies are not interchangeable.

The board is fragile — read before soldering

This is the most important thing to know before working on a +2. The Amstrad-produced Sinclair boards are of notably poor PCB quality, and great care is required when replacing components to avoid lifting pads or tracks.

Working rules:

• Use a temperature-controlled iron with a clean fine tip at a moderate setting. Heat that is too low forces long dwell times, which is what actually lifts pads.
• Add fresh leaded solder and flux to every old joint before removing anything — mixing new solder into a forty-year-old joint lowers its melting point and makes removal much cleaner.
• Keep dwell times short and let the area cool between attempts.
• Never lever a component out until the joint is visibly molten.
• Support the board and do not flex it. Flexing cracks tracks and breaks connector joints.
• Socket rather than re-solder where a chip may need to come out again — RAM in particular. Fitting sockets once is kinder to the board than repeated desoldering.
• Clear each hole fully with wick or a vacuum tool before moving the part.
• Inspect for solder splatter afterwards; hairline bridges can measure several ohms and cause misleading faults.

The Service Manual likewise requires recognised desoldering and heatsinking technique and an earthed, low-power iron.

Opening the case

1. Unplug the power and all peripherals.
2. Remove the six case screws from the underside.
3. Separate the halves carefully — they remain joined by the keyboard ribbons and the tape deck connector. Disconnect both.

Handle the keyboard ribbons gently: ease them in and out squarely, and make sure they are fully home and not kinked when refitting.

Datacorder servicing

The integral cassette deck is the part most likely to need work. Problems arise from dirt, dust, heat, corrosion, physical damage to the keys, perished drive belts, mechanism wear and previous poor repairs.

Drive belt

Replacing the belt is the standard first job on any unserviced +2. The original belts perish, stretch and go sticky with age, which causes wrong tape speed, failure to load or save, and eventually complete failure to move the tape. Replacement belts are readily available.

Access the deck by removing the six case screws and separating the halves as above.

Head cleaning and azimuth

• Clean the head and the pinch roller and capstan with isopropyl alcohol on a lint-free swab. Oxide build-up alone will stop a machine loading.
• Check the azimuth — the head's angular alignment. With a tape playing, adjust for the sharpest, brightest tone; a note that sounds even slightly muffled will not load reliably. This is exactly the adjustment the Repair Data section of the Spectrum servicing manual describes for external recorders, and it applies just as much to the built-in deck.

Grounding — the audio hum fix

Taiwanese-built +2s are known for buzzing or humming on the audio output, present all the time because the audio output is live even when the deck is not running.

The tape PCB uses the metal frame of the tape mechanism to route ground paths between different parts of the board. Checking that the two screws attaching the PCB to the mechanism are tight and conductive usually fixes the problem completely. This is worth doing as routine maintenance whenever the deck is out.

Keyboard

The +2 uses a membrane under a moulded keyboard. Membrane failure is the usual cause of dead keys, and replacement membranes are still manufactured.

• Check the tails are clean, undamaged and fully seated before suspecting anything electronic.
• Insert the tails with a slight side-to-side movement while easing them down, and do not kink them.
• A dead block of keys almost always indicates a tail or connector problem rather than a failed chip.

Cooling and the regulator

• Ensure good contact between the 7805 regulator body and its heatsink, and apply fresh thermal grease when refitting or replacing it.
• The ULA was supplied with an Amstrad clip-on heatsink. If it is missing, fit one — particularly on a machine whose ULA has been replaced.
• After a few minutes' running, the ULA and regulator should be warm; RAM chips should not be. A warm RAM chip is a failing one.

Power checks

A healthy +2 draws roughly 800 mA to 1.2 A depending on the RAM fitted. Testing on a current-limited bench supply set to about 1.5 A is a quick way to catch a shorted chip before it does further damage.

The on-board rails are +5 V from the 7805, ±12 V from the TR4/TR5 inverter and its charge pump, and −5 V from the −12 V rail via a zener for the expansion port.

The external supply should not sag below 7.0 V at 1.4 A with low mains, nor peak above 13 V at 600 mA with high mains.

Cleaning

• Case: mild detergent on a damp cloth. The grey plastic marks easily and yellows with UV.
• Keyboard: clean the key surfaces; the membrane and its tails should only be cleaned gently and dried fully.
• Board: brush and low-pressure air; clean the edge connector fingers with a soft eraser and contact cleaner.
• Datacorder: clean the head, capstan and pinch roller with isopropyl alcohol whenever the case is open.

Common failure points

ZX Spectrum +2 — failure-prone items

Item	Symptom	Action
Datacorder drive belt	Won't load/save; wrong speed; tape doesn't move	Replace the belt
Tape head / azimuth	Loads unreliably or not at all	Clean the head; adjust azimuth
Tape PCB grounding	Constant hum or buzz on audio	Tighten and clean the two PCB-to-mechanism screws
RAM	Crashes, corrupt display, board draws excess current	Test with a diagnostic ROM; socket and replace
PCB quality	Lifted pads/tracks after rework; thermal intermittents	Careful soldering technique; inspect for hairline cracks
Keyboard membrane	Dead keys or dead block of keys	Reseat/clean tails; replace membrane
ULA heatsink missing	Warm-related instability	Refit a heatsink
Power transistors	No video or serial output	Fit ZTX651 in place of a failed/under-rated ZTX650

Recommended tools

• Small Philips/Pozidriv screwdrivers and an anti-static strap.
• Temperature-controlled soldering iron with a fine tip, solder wick or a vacuum tool, fresh leaded solder and flux.
• IC sockets (for RAM), IC extraction tool.
• Digital multimeter; a current-limited bench supply is very useful.
• Oscilloscope for clock and RAS/CAS work.
• Isopropyl alcohol, lint-free swabs, contact cleaner, soft eraser.
• Replacement Datacorder belt and keyboard membrane.
• Optionally a diagnostic test ROM for RAM testing.

See Recommended Tools for the general toolkit.

Preventive maintenance checklist

1. Replace the Datacorder drive belt; clean the head, capstan and pinch roller.
2. Tighten and clean the two tape-PCB grounding screws.
3. Check the 7805 heatsink mounting and re-grease; confirm the ULA heatsink is fitted.
4. Check current draw is within 800 mA–1.2 A.
5. Clean the edge connector and reseat the keyboard tails.
6. Inspect the board for lifted pads and hairline cracks, especially around any previous rework.

Related pages

• Sinclair ZX Spectrum +2
• Sinclair ZX Spectrum +2 Troubleshooting Guide
• Sinclair ZX Spectrum +2 Capacitor Replacement Guide
• Sinclair ZX Spectrum+ General Maintenance
• Sinclair ZX Spectrum Keyboard Membrane Repair
• Capacitor Failure Symptoms · Recommended Tools