Power supplies: measure before you trust
An old power supply can still show signs of life and yet deliver too much or too little voltage. Measuring the outputs takes a few minutes and protects the machine.
Difficulty: Take careTime: 30 min
⚠ Before you start
- Only measure the low-voltage outputs (the contacts on the plug that connects to the computer). Never open the case of a power supply that is plugged into the mains.
- Don't open sealed power supplies to repair them at home: the 230 V side is dangerous, even after being unplugged.
Amiga
The external power supplies of the A500, A500 Plus, A600 and A1200 provide +5 V, +12 V and −12 V. The critical value is the +5 V: it should be between 4.75 V and 5.25 V. Voltage below that causes unstable start-ups; above that it can damage chips.
A measurement with no load can be misleading: some power supplies only show the problem when they are powering the machine. If in doubt, the best solution is a modern power supply made for the Amiga; these are on sale and are more efficient and safer.
Spectrum
The Spectrum 16K, 48K and Spectrum+ use a 9 V DC power supply and produce the 5 V on the board itself. Before using an alternative power supply, check the voltage and plug polarity shown on the original power supply's label: a power supply with the wrong polarity can damage the computer.
The 128 and the grey +2 also use a simple 9 V power supply. The +2A, +2B and +3, however, use a different power supply, with several voltages and its own plug. Don't swap power supplies between these groups, even if the plug seems to fit.
How to measure
- 10Plug the power supply into the mains without connecting it to the computer.
- 20With the multimeter set to DC voltage (V DC), measure between the ground contact (0 V) and each output.
- 30Compare with the nominal value. On the Amiga, the +5 V output is the one that matters most.
When to bring it to us
If the voltages are out of range or the power supply gets hot, smells or makes noise, don't use it. We can test it under load or fit a safe alternative.
Request a repairThese guides are for information. Working on old electronics carries risks: do it at your own risk, with the machine unplugged, and never open power supplies or CRT monitors. If in doubt, bring the machine to us.