View Full Version : Power Supply Dead??

08-01-2001, 05:32 PM
I have an old PM 7500, upgraded to 400Mhz G3 via carrier zif, and an UW Jackhammer with 2 9gig Barracudas, and an ati 128 card, 448MB RAM, and it started to act strange, locking up and such, monitor flickering, after having been extremely reliable for many years.

Last night, I turned it on, it worked for awhile, and I was testing with extensions off, and it froze up. Not an extension problem I though. When I went to reboot, I got no chime and black screens, but still had power to the fan in the power supply. I hit the interrupt swith, and went to restart, and then nothing happened.

The Green LED flashes once, and I hear a click and Buzzing from the power supply. THe fan does not spin up on the power supply, nothing. As things started to act strange, I did check the PRAM Batt, and it was fine.

So Is the power supply dead??? Is there a way I can use my Multi meter to test it??

I look forward to your replies, as I respect the opinions of every member here. Someday, I hope to loose the jr. in front of member myself.


08-02-2001, 02:23 AM
All it takes is a certain number of posts. It's an integer higher than 10 and less than 50. Just keep asking intelligent questions and demonstrate a keen willingness to learn, and you'll be a Member in no time.

Sounds like a power problem to me. But I've never had one fail. Let's see what louie has to say...

http://www.macgurus.com/ubb/batlogo.gif Batsignal invoked to louie!

08-02-2001, 10:12 AM
Magician likes to test the power output off of a spare 4-pin molex connector. This won't test all of the voltages the power supply puts out but...

Turn the machine on. Test voltages on a spare 4-pin molex power plug connector like you put into a CD-ROM drive or hard drive. What you are looking for, as I recall yellow to ground should be +12v and red to ground should be +5v. Be careful you don't short anything.

Another point is that you may as well remove the PS and look inside. There may be a fuse in it (which may be blown for good reason or not, possibly a momentary voltage surge from your friendly power company) and there may be a button style battery in it (I would think tho that this would not cause a failure during operation, only at boot up). k

08-02-2001, 01:31 PM
Some Mac models act that way when the PRAM battery dies. I'm not sure if the 7500 is one of those or not. Check that battery anyway ($10 at Radio Shack).

08-02-2001, 06:02 PM
Kaye and Louie

Thanks for the reply. The PRAM Battery is good, fairly new, and I tested it with my multi-meter. I have the PS Pulled out, and will try to open it to see if there is a fuse inside.

The fan on the PS does not spin up, and I hear a click from the power supply when I hit the power button.

I will post my findings later

Once again thanks, great forums!!

08-19-2001, 11:19 PM
A follow up.

I did test the battery under load, as I pressed the button, and it was putting out the right voltage. I swpped power supplies with a working 7500 I picked up cheap, and all is fine.

08-20-2001, 01:04 AM

Thanks for the followup. Glad your 7500 is living again. k