Sinclair ZX80 / ZX81 / Z88 Forums

From reading previous posts the polarity of the Spectrum jack is reversed? No real confirmation though.

So + on the outside barrel/ring and - on the inside barrel/ring?

Whereas T'ZX81'000 is + tip and - ring?

Having trouble discerning polarity from traces on refurbished Spectrum 48 (thanks Bytedelight!)

Thought I would never find it...from WOS

ZX80, ZX81 use a 3.5mm “audio” jack plug (U.K. terminology). Tip is +9V (nominal). Ring/sleeve is 0V/GND

ZX Spectrum 16K/48K/+/128K/+2 (grey) all use a 2.1mm (I.D.) “DC” barrel power connector. Outside is +9V (nominal). Inner contact is 0V/GND.

Please note that there is, and never was a standard polarity for these barrel power connectors, manufacturers using whatever polarity they felt like at the time. In the 1980s, it was about 50/50 to 60/40 of one polarity compared to the other for gadgets used inside the home. But most gadgets designed for use in a car had the negative on the outside contact.

Mark

The referenced WoSf thread is here

Mark

Thanks for the definitive answer.

Please note that there is, and never was a standard polarity for these barrel power connectors, manufacturers using whatever polarity they felt like at the time. In the 1980s, it was about 50/50 to 60/40 of one polarity compared to the other for gadgets used inside the home. But most gadgets designed for use in a car had the negative on the outside contact.

That is how I ruined someone's laptop years ago. ...no standard...I still feel stupid. Polarity! Should have remembered to check it.

Also, sometimes the barrel connectors are used for low voltage (4.5V to 30V) AC from external “power bricks” (just a transformer in a case). These are very good at killing devices that are expecting a DC supply. In a ZX Spectrum, such an AC supply will kill the 7805 voltage regulator, some electrolytic capacitors and the transistors that form the DC/DC converter/inverter circuit (that supplies the lower RAM and some of the video circuitry).

Mark