Stack Exchange Network
Stack Exchange network consists of 181 Q&A communities including
Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.
Visit Stack Exchange
Retrocomputing Stack Exchange is a question and answer site for vintage-computer hobbyists interested in restoring, preserving, and using the classic computer and gaming systems of yesteryear. It only takes a minute to sign up.
Sign up to join this community
Anybody can ask a question
The best answers are voted up and rise to the top
2 years, 6 months ago
I got a working ZX Spectrum 48k (issue 6a) with the original power supply.
Before hooking up the power supply I tested with my multimeter to see if it was good. The power supply specifies it outputs 9V but my multimeter says 15V. To be safe I didn't use it.
Is the power supply malfunctioning? Or is this normal?
1,729 1 1 gold badge 14 14 silver badges 26 26 bronze badges
Nov 11, 2020 at 13:15
JV Lobo JV Lobo
293 1 1 silver badge 6 6 bronze badges
This is relatively normal for the original PSU.
The supply unit is a "soft" one that will output a much lower voltage under load when connected to the ZX Spectrum. 12 or even more Volts are normal.
Nov 11, 2020 at 13:31
30.7k 4 4 gold badges 76 76 silver badges 150 150 bronze badges
A 48K ZX84 uses between 0.4 and 1Amp (
A 22.5Ohm resistor will simulate a 0.4Amp load. The nearest standard values are 22Ohm or 24Ohm.
If you have (or can buy) a resistor of this value (and at least 7 Watt power rating) you can use the resistor as a dummy load to check the PSU.
To test on full load you'll need a 9.1Ohm, 16W resistor.
NB, the resistance values are for 9V, but the power ratings are for 12V.
Nov 12, 2020 at 15:12
131 4 4 bronze badges
Original PSU is "soft", which means the real voltage depends on current consumption. I.e. 9 volts (nominal) is under the full load. With no load, it could be much higher.
Nov 12, 2020 at 9:16
Martin Maly Martin Maly
5,327 16 16 silver badges 43 43 bronze badges
log in to answer this question.
Not the answer you're looking for? Browse other questions tagged
By clicking “Accept all cookies”, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our
Accept all cookies
Necessary cookies only