Can anyone point me towards some resources to trouble-shoot what I believe is an Applied Engineering power supply? I've had a fair amount of success saving Apple-brand power supplies, but the AE model is a completely different animal in terms of components and complexity. It's a black box, shorter than the Apple models, labeled Model PS-A, has a 120/240 external switch secured with a plastic tab and is rated +12V 3A, +5V 6A, -12V 1A and -5V 1A. It came with a lle which ran intermittently and then gave up the ghost. No obvious sign of component failure, no cloud of smoke and no stink. Currently it's outputting +5.16 on pin 3, +11.18 on pin 4, -9.83 on pin 5 and -4.54 on pin 6. I am a non-tech person but would describe my self as "handy" when it comes to electrical issues. Any advice would be appreciated.
Are those measurements with the load (the computer) attached, or with no load?
The positive rails are within 10% tolerance but the negative rails are a little off. Many supplies, however, need a minimum load before they regulate their output.
Measures were taken with no load. I'm reluctant to risk screwing up the motherboard if the power supply is significantly malfunctioning
Voltages are always off on an Apple II power supply without a load.
In the past I’ve connected an old hard drive to one to provide a load.
A 12v "high intensity" light bulb works well as a load too. You can put one on the 12v line and another on the 5v line. It's probably not necessary to load the -5 or -12v lines since they are fairly low current anyway.
I repaired an AE MWP-302 power supply by replacing the board with a newly made Mean Well PT-65B and an added LM7905 regulator for the -5V supply. That conversion is documented on a thread originated by Uncle Bernie here on AppleFritter. The supply that I did was basically the same size as a normal //e or ][+ power supply though, not shorter. His original work was with an Apple power supply, I adapted it with a slightly different mounting technique for the AE supply. I've since done one using my plastic mounting version in an original Apple power supply box also. The methodology should work for the supply you have as well as the Mean Well PT-65B board is smaller in both length and width than the Apple ones so it should fit even if your case is shorter.
The thread that power supply conversion was in is here:
https://www.applefritter.com/content/putting-pt-65b-switchmode-power-module-apple-iie
It doesn’t need to be high intensity. In fact the nominal current on the 12V rail is 1.5A, therefore any light bulb that is more than 18W can damage it. You want to use a small incandescent 12V bulb, ideally not more than 5W. Do not load the negative voltage rails. If you have the correct voltage without a load, they are fine.
Readily available incandescent 12V bulbs both for automotive and home lighting can be above 50W, so don't use those.
CVT wrote:
the nominal current on the 12V rail is 1.5A, therefore any light bulb that is more than 18W can damage it.
Which is a good reminder. The bulbs I was recommending are 12v / 12W, so should only present about a 1A load on the 12v supply and less on the 5v supply.
12v bulbs.jpg
I think it's not common that a low-power appliance bulb is what is meant by "high intensity". The phrase is much more common with respect to HID (high-intensity discharge) sources, which are not at all suitable as test loads.
Why does every discussion here have to devolve into a pissing contest? Sorry if I used the wrong terminology. Everything here is VINTAGE. The vintage incandescent bulbs I refered to are marked "high intensity" on the package, which was probably true 40 years ago when these were made for desktop task lighting. Obviously an HID arc lamp wouldn't be suitable for this purpose.