PSU Polarity

A place to discuss the ZX80's and ZX81's younger brother - the Sinclair ZX Spectrum
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gammaray
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PSU Polarity

Post by gammaray » Fri Oct 05, 2018 10:15 pm

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!)
5-TS1000,UK ZX81<-Sheelagh, US ZX81, 2-TS1500/KDLX , 3-TS2040 printer, 2-TS2020 cassette decks, ZXPAND+AY, ZeddyNET, ZXBlast, UDG, ZX8CCB, AERCO, BUILDS/REPAIRS ZX Spectrum, ZX80 Minstrel, ZXMAX48 v1 v2, 2-TS-2068, ROM, 16kRAM

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gammaray
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Re: PSU Polarity

Post by gammaray » Fri Oct 05, 2018 10:48 pm

Thought I would never find it...from WOS
power supply polarity.jpg
5-TS1000,UK ZX81<-Sheelagh, US ZX81, 2-TS1500/KDLX , 3-TS2040 printer, 2-TS2020 cassette decks, ZXPAND+AY, ZeddyNET, ZXBlast, UDG, ZX8CCB, AERCO, BUILDS/REPAIRS ZX Spectrum, ZX80 Minstrel, ZXMAX48 v1 v2, 2-TS-2068, ROM, 16kRAM

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1024MAK
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Re: PSU Polarity

Post by 1024MAK » Fri Oct 05, 2018 11:29 pm

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

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1024MAK
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Re: PSU Polarity

Post by 1024MAK » Fri Oct 05, 2018 11:33 pm

The referenced WoSf thread is here ;-)

Mark

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gammaray
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Re: PSU Polarity

Post by gammaray » Fri Oct 05, 2018 11:47 pm

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.
5-TS1000,UK ZX81<-Sheelagh, US ZX81, 2-TS1500/KDLX , 3-TS2040 printer, 2-TS2020 cassette decks, ZXPAND+AY, ZeddyNET, ZXBlast, UDG, ZX8CCB, AERCO, BUILDS/REPAIRS ZX Spectrum, ZX80 Minstrel, ZXMAX48 v1 v2, 2-TS-2068, ROM, 16kRAM

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1024MAK
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Re: PSU Polarity

Post by 1024MAK » Sat Oct 06, 2018 6:27 pm

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

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