AT power supply for my 486 questions \ VOGONS

AT power supply for my 486 questions

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First post, by Turboman

Posted on 2015-07-15, 23:57

Turboman Offline

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I have several old 486 era AT PSU units, they all turn on but I have a questions about the voltage readings.
I noticed on one I get a reading of -6v on the -12v and -4 on the -5, on another I get -11v and -5, and on another one I get -10 and -4, All of the + voltage looks good I am testing them by just turning them on not plugged into anything.

I assume these PSU that are reading low are no good and I should look for one that shows as close to the voltage as possible?

I may need to get some replacements PSU for my other systems I know there has been some recommend that are on ebay but I don't have any links.

Reply 1 of 3, by darksheer

Posted on 2015-07-16, 00:07

darksheer Offline

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It's not recommended to turn on PSU without devices plugged on...
If you don't mind using period correct hardware just put an ATX PSU with an AT to ATX adapter (you'll save yourself a bunch of troubles like having to change the capacitors or others components).

Reply 2 of 3, by Turboman

Posted on 2015-07-16, 18:55

Turboman Offline

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I'm still interested in knowing what affect those readings would have I don't want to fry anything. I was also thinking of getting an ATX PSU but I don't know good ones to look for that would suit 386/486 PC. I have a older generic AT switching PSU that works but I don't know if it is good for my MB-8433UUD, It shows

Watt +5V -5V +12V -12V

150W 15A 500mA 5.5A 500mA

180W 18A 500mA 7A 500mA

200W 20A 500mA 8A 500mA

230W 23A 500mA 9A 500mA

250W 25A 500mA 10A 500mA

275W 27A 500mA 10.5A 500mA

Reply 3 of 3, by Jepael

Posted on 2015-07-17, 08:19

Jepael Offline

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Put some load on there when measuring power supplies. For a dummy load just buy some resistors or put some old hard drives (can be broken ones but they must still be spinning to draw enough power. CD drives won't work as they don't draw enough power as they just sit there without spinning). The power supply circuitry may be out of regulation if there is no load. This is normal at least for AT era supplies.

I have no idea what would be enough for a dummy load, but maybe 1A of both 12V and 5V, and maybe 0.1A of both -12 and -5V.

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