ZX Spectrum Repair - Before You Plug In

Required Tools

Philips Screwdriverhttps://store.ifixit.co.uk/collections/drivers-wrenches?pf_t

Without the power supply connected

Unscrew the board from the bottom case by removing the single screw in the middle of the board and lifting away

Voltage regulator

Turn multimeter to 200K Ohms

Put the black probe on the ground

Hold the black probe against the heatsink to ground

Place the red probe onto the left pin of the voltage regulator. This should over a few seconds build up to over 100.

If it is less than 100 then you have a faulty regulator and should be replaced. You can get modern replacements that improve heat from the Spectrum and allow you to remove the heatsink completely from here – RetroRevival.

Lower RAM

Turn multimeter to 2K Ohms and put the black probe on the ground and on the lower ram chip at the bottom left check the following pins:

Pin 9: Ideally around 300 but can be 400-500. Much less suggests a problem.

Pin 16: Close to 0. Anything else suggests a broken track on the circuit board

Now change multimeter to 20K setting

Pin 8: 2.6-2.8k Ohm on an issue 3 board and above. Or 800-900 on an issue 2

Now change to 200K setting

Pin 1: Ideally between 4-500. Min of 300. Less than that suggests a problem

Inductor coil

Turn the board around and find the pins for the inductor coil as shown below

Inductor coil ZX Spectrum

With the meter on 20K measure between the top and bottom pin on both sides of the coil. The meter should read 0

Now measure horizontally opposites

The meter should read 1 or open circuit

Place the multimeter in Diode test mode. The icon should look like the below


Check Diodes TR4 and TR5


For these diodes the centre leg is called “the base leg” and the ones to each side are called the “collector” and “emitter”

Hold positive (red) probe to centre (base) leg.

Now use the black negative probe to check the collector and emitter legs. They should both read around 0.6 to 0.9V

Replace positive probe with negative on the base leg and repeat the test with the collector and emitter legs, this should indicate an open circuit on the meter.


Hold negative (black) to base centre leg. Positive (red) to other legs should show 0.6 to 0.9V on collector and emitter legs. Swap to positive on base centre leg and test again to see open circuit on collector and 1.2v on emitter.