Spectrum ZX powerbrick

I got lucky again at the local flee market when i managed to get a Spectrum ZX powerbrick.

Some basic information:

Input: 240V AC, 50Hz
Output: 9V DC, 1.4A (without peripherals 700mA would do but not recommended)
Center Polarity: -ve (inner diameter is 2.5mm and it’s center negative)

However when connected the power, adapter was dead. So it was time to call in the superhero in form of my friend, who also happens to be an electronics engineer. He managed to tear the thing apart, its easier than with the commodore adapters which are sealed with epoxy, Sinclair only used three flat screws.

The design of the power adapter is very basic, just a transformer couple of capacitors and that’s almost it.

However when my friend unsoldered the transformer it had a surprise underneath.

A thermal fuse TCO 115 117C, designed to be cut when 16A continuous current passed through it, or it heated to more than 117°C.

After the thermal fuse was replaced the powerbrick started working again. As a fun fact, the original adapter has a throughput of 15V when not connected and 13,45 V when connected to a load. The Spectrum is declared to work at 9V, but it’s capable to work even with higher than specified voltages. It is truly designed like a Russian tank as most of the electronics of the era. However it is recommended to use a modern swiching adapter, which gives a more constant and stable output, which directly translates in less heating of the passive elements and longer lifetime.

Modern swiching adapter, 9V with negative center and 5.5 mm x 2.5 mm barrel male connector at the end.

Different Spectrum power bricks, top left are the 48k ones, other are for Spectrum +2, +3. Note that there is also UK 700 mA version.

Most common type in central Europe produced in W Germany.

Reference if you want to know more:

A more technical video (Video is not mine).

Retro Computing Edit description collection.onceuponabyte.org

Spectrum ZX powerbrick

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