How to test power supply

#1 Sat, 21 Mar 2009 - 12:48 68kMLA

hello

i've found some old apple II parts with 3 power supply inside cases and 2 others one "alone"

should i test them with the ATX pc way, putting a cable between green and black cable with multimeter on 20V and nothing else plug on it ??is there any risk to "burn" power supply ?

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#2 Wed, 25 Mar 2009 - 22:23 68kMLA

The Apple II power-supply is fairly "intelligent". If it detects a no-load situation (that is, nothing is taking the electricity), it will short-circuit itself indefinitely. This will come out as a rapid clicking noise, which is quiet, but can still be heard. Likewise, if there's ever a short circuit, the power supply will shut down for a moment, then attempt to restart. If the short-circuit condition is never removed, this cycle will happen indefinitely, producing the same rapid clicking sound as before.

#3 Thu, 26 Mar 2009 - 13:05 68kMLA

thanks for this info, so i can just plug power supply "alone" and if i heard the noise, that means power supply works ?? i can do it with no risk to damage power supply ??

i want to be sure i can do that and don't burn it

#4 Thu, 26 Mar 2009 - 14:50 68kMLA

thanks for this info, so i can just plug power supply "alone" and if i heard the noise, that means power supply works ?? i can do it with no risk to damage power supply ??

Well, the best test is to plug the power supply into an Apple II, but if you hear the clicking when the power supply is not plugged in to an Apple II, then that is a decent test as well. You shouldn't damage the power supply, but don't leave it on for a long time, just a few seconds.

#5 Thu, 26 Mar 2009 - 19:57 68kMLA

ok thank you

#6 Sat, 28 Mar 2009 - 16:03 68kMLA

I always use a hard disk -- one that is usable but disposable -- for 12V and 5V testing. It is easy to make a test cable (with tapping points to measure voltages) from salvaged wiring and the disk almost always draws enough power to start up a switched mode PSU.