sondeen@isi.edu (Jeff Sondeen) (03/19/91)
Here are the responses I received to my dead power supply request for info. Indeed, a new power did the trick! /jeff From: poffen@sj.ATE.SLB.COM (Russ Poffenberger): >Problem: apparent power supply death >Question: how not to kill the replacement? > >I have an clone 386 (2 years old) whose power supply (230 watts) died >during power up one day, now making only a faint humming noise which >fades like a motor running down when turned off. > >This followed a few weeks after my successful addition of 4 more Megs >of memory (totalling 8); there are also 2 hard disks but the vendor >thinks there's no power overload. The vendor recommended >disconnecting cards and connectors one at a time to check for shorts >causing the power supply to go into "protect" mode. No disconnections >seemed to bring the power supply back alive. A new one costs $45; >however, how can I be sure that I don't fry the new one when I put >that in? > >Thanks for any advice. You should note that most power supplies of this type will appear dead (no output) if they are totally disconnected. ie, they need some small load in order to work properly. As far as the new supply, it is unlikely that a short or other condition caused the failure of the original since they are so well protected. You should feel safe installing the new one. Even if there is a short, the supply will protect itself and not be damaged. Power supplies do fail now and then, just one of those things. Russ Poffenberger DOMAIN: poffen@sj.ate.slb.com Schlumberger Technologies UUCP: {uunet,decwrl,amdahl}!sjsca4!poffen 1601 Technology Drive CIS: 72401,276 San Jose, Ca. 95110 (408)437-5254 --------------- From: jhamill@spca.bbn.com: ... Get ahold of an ohmmeter and check the resistance between all the positive inputs on the motherboard and ground. There are +5 and -/+ 12 volt inputs. If you have a reading that's round 0 ohms you have a short. Not likely though. Your power supply probably just died. A reading around 100 ohms would probably be ok (or higher). John --------------- From: Tom Knotts <knotts@hpl-opus.hpl.hp.com>: You need to disconnect the leads from the supply to the system. Turn it on and measure the voltage. Then you must supply an external load to see if the voltage holds up. If there is something wrong with the supply, I would recommend replacing it. Switching supplies are tough to fix. tom --------------- From: wdarden@nrtc.northrop.com Hi Jeff, DO NOT risk damaging your motherboard, memory, controllers, keyboard or disk drives with a bad power supply. Buy a new power supply. I repair AT/XT power supplies and the most common failure is either a rectifier diode or a switching transistor. I have repaced bad capacitors and switches as well. To test the power supply, place a load on the +5V lead to ground of at least 2 Amps. Good luck, BiLL..... -- /jeff sondeen@isi.edu "engineers were discouraged from bringing problems to the attention of their supervisors" -- John Magnus, final report, Hubble Space Telescope investigation