520ST external power supply

Repairs & upgrades.
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coonsgm
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520ST external power supply

Post by coonsgm »

I've been looking into alternatives to the 520ST external power supply and as I've been looking into them I see the following pinout showing +5V, +12V and -12V inputs.

From what I've read with the STF and newer, the +5V is the primary input for running most of the board, the +12V is for the floppy drive and video circuitry (please correct me if I'm wrong).

Given that the original 520 doesn't have a floppy drive to power, why would it need the -12V input?
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exxos
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Re: 520ST external power supply

Post by exxos »

-12V is for RS232 stuff on the ST. STF had a built on negative voltage regulator, which the ST does not have.

ST.JPG
ST.JPG (30.93 KiB) Viewed 1550 times

STF.JPG
STF.JPG (128.21 KiB) Viewed 1550 times
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coonsgm
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Re: 520ST external power supply

Post by coonsgm »

Ah, makes sense! Thank you.
Steve
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Re: 520ST external power supply

Post by Steve »

You can quite easily use a Pico PSU for a short-st, see my blog:

https://www.exxosforum.co.uk/forum/viewt ... f=9&t=4617
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rubber_jonnie
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Re: 520ST external power supply

Post by rubber_jonnie »

Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
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