-5v way over!

[KillerBug]

Ok, I am monitoring my Power supply right now, the -5v is giving me -5.714v.

How do I fix this? Would a normal 5v voltage regulator fix the problem? If so, would I use it the normal way? What parts use this?

[Wiz]

a friend of mine ha the same problem. Soyo told him that a fluctuation leike that was normal. But i doubt it, as everytime you turn on his system, you get a shock.

[scotter]

if its a new power suppy take it back and get a new one the voltage regulater in it is bad that is tooooooo high

[tonym]

KB,

The tolerance on this supply output is +/-5%. This means it can range from -5.25V, min. to -4.75, max.

The -5.714V value indicates that the internal regulator inside the P/S is bad...probably shorted in-to-out as these are low-dropout versions of the uA7905 regulators and the primary failure mode is shorted I-O.

Replace the P/S ASAP! Even though you won't nuke anything on your mobo with this voltage value, you will shorten the mobo's life expectancy by using this P/S much longer.


Tony

[KillerBug]

I replaced the suppy, but I don't want to throw it out, other than that, it is the best supply I have, with special features to cool the CPU extra, and it is the only power supply I have that will run a TEC and the system at once. So will putting a 5v voltage regulator in the line fix the problem, or blow up the board.

[tonym]

KB,

Open the P/S and try to find out the part number of the regulator. It should be in a 3 pin TO-220 case (looks like a plain old power transistor). Just follow the -5V wire back to the PCB and then the trace back to the regulator! Since the -5V draws so little power, there's an excellent chance that it's just a three-terminal linear regulator.

I probably have a few here in the stock room, so if you get the number, I'll send you a couple if I have 'em!

If you're not sure and have access to a digital camera, just take a picture and post it here and we can figure out what's wrong and the guilty parties that way!!!


Tony

[This message has been edited by tonym (edited 06-02-2000).]

[alpha]

Don't use it on a mobo! It could get worse - my 12 or 5v line (not sure which) went bad and torched a mobo - it went real bad - like 15 or something!! You could smell the ozone from the burning transistors in the room for weeks! I havn't had a system for 2months 'cos of that!

[Wiz]

Just a quick question, is the CPU overclocked Killerbug? If so, reduce the speed back to normal and see what happens.

[alpha]

I agree with Wiz - mine went 'cos the CPU was drawing like 60watts of power at 550mhz, as well as trying to fuel 2 harddrives, an FDD, a sound card, a mobo and a stinking hot Permedia2 (the one with torched off my skin http://sysopt.earthweb.com/forum/smile.gif)

[tonym]

Folks,

The power supply is designed to protect itself in the event of an overcurrent (too much power draw). The current from the output will "foldback" and the output voltage will DECREASE!

The -5V output is a low current supply, 0.5A or less. This means that it uses a linear regulator from the -12V supply (which is a 1A or less output) to derive this voltage. The fact that KB's power supply has a voltage greater (less negative) than -5V indicates that one of two conditions exist:

1.) the P/S is bad -- the -5V linear regulator has died, or

2.) something on the mobo is bad and is steering current away (out of) the -5V output. The power supplies that we use are voltage sources, not voltage references. Each positive output is designed to source current (i.e. have drawn from) and each negative output is designed to sink current (have drawn to). If there's a fault on the board, a strange situation may exist where the regulator cannot regulate the output voltage with the fault present...it in fact becomes reverse biased and turns off.

KB, take my advice...you really don't want to troubleshoot this without the proper equipment. You can easily determine if it's the mobo if you replace the supply with another. If all works well, then it's the P/S.

If it is the P/S, my suggestion is to trash it. It isn't worth the aggravation of fishing around in the supply if you don't have real good soldering experience or are unfamiliar with discrete electronics. P/S manufacturers cram 10 pounds of **** into a 1 pound box, and the supply is meant to be a throw-away upon failure. Honest-to-god!!

Buy another one!


Tony

[KillerBug]

I did replace the supply, it works fine, I just don't want to toss this other supply, and I am just asking if I can use a 5v voltage regulator from radio shack to do the -5v job.