ScuzzBlog: Diaries February 2024

Entry 3rd February 2024: Post 1: Sinclair ZX - Crash course in power supplies.

Sinclair ZX - Crash course in power supplies.

Before I plugged in my ZX Spectrum units I have laying around I
thought I would take a refresher on just what power supplies are
suitable. The rule of thumb is that all power supplies with the
exception of the ZX80 and later Plus2 and Plus3 are backward
compatible but not forward compatible. Meaning you can use any
supply on an earlier computer.

Few ground rules: The centre terminal on the 2.1mm barrel connector
is negative. Important cus a lot of power supplies are centre
positive. Also the supply is 9V DC though the computers generally
run on 7.5V to 12V.

The power supply for the ZX80 is suitable only for the ZX80.

The earlier power supplies can fail and damage your computer and
so the 700/1200/1400 original case types are used with caution.
It is wise to check the voltage supplies are correct. The units
are safe to handle once unplugged. Inside is a thermal fuse and
that reacts to heat.

OK Which power supply went with what computer:

ZX80: Unique and so ignore.

ZX81 700: Would generally have had the 700 mA unit and can cope
with the base unit without any expansion that uses power. Use
with caution.

ZX Spectrum 16K 1200: The earlier machines had the 1.2A 1200 unit
and would generally be safe to use on any of the rubber key computers.
Use with caution.

ZX Spectrum 48K 1400: The standard Spectrum used the 1.4A 1400
type unit and suits all rubber keypad machines. Again though use
with caution.

ZX Spectrum+ 1400: The plus/+ was simply a basic 48K Spectrum
housed in a new case. Same goes for the 1400 1.4A power supply.
The unit may be marginally newer but should generally still be

ZX Spectrum+ 128K: This has the ribbed heat sink. The black PSU
has a distinctive ribbed patterned panel to one side unique to
the 128K Spectrum. Whilst backward compatible should not be used
on the +2 grey unit. Be mindful that the Spectrum+ and earlier
power supplies are not suitable for the 128K. Be careful of getting
power supplies mixed up because the black ones can look the same
in certain light. Only the 128K has the ribbed pattern edge.

The 128K power supply rated 1.85A unlike the Spectrum+ at 1.4A.

ZX Spectrum+2 Grey 2.1A: The Holy Grail of all power supplies. The
grey ZX Spectrum+2 with tape machine has the 9V 2.1mm barrel and
so will fit all earlier ZX Spectrum models. Totally backward
compatible. It also has the different connector to the later black
Spectrum +2 and so can not be used accidentality.

Rated 2.1A it is higher rating and last of the unregulated supplies.
The distinct grey colour of this unit makes it truly the only PSU
you will ever need for your Spectrums. A great find if you can
get hold of one.

ZX Spectrum+2 Black: First regulated supply brick and should only
be used on the Plus2 Black. Do not use on the +3 as it will
eventually burn out.

ZX Spectrum+3 Black: Second regulated supply and suitable for both
the +2 and +3 black machines. Both models have a different supply
connector to any of the earlier models.

End technical blurb:

I did kind know all that in truth as in my trolley unit next to
the bench is a my stock of PSU units for my machines and I only
really keep the grey one out and use it on all my ZX Spectrums
that can take the connector. Still worth checking out all the

Sinclair ZX - Crash course in power supplies.


ZX81 700

ZX Spectrum 16K/48K 700,1200,1400

ZX Spectrum+ 1.4A 1400 new casing black

ZX Spectrum+ 128K 1.85A black with ribbed pattern black case

ZX Spectrum+2 grey case 2.1A grey power supply.

ZX Spectrum+2 black case regulated brick supply

ZX Spectrum+3 black case regulated brick supply

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Last updated 3rd February 2024

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