PSU got negative output!! help

[jdimpas]

hello guys, my powersupply is working however it has a negative output. Once i power on my computer the fan of the processor works but the entire system won't work. When I checked the output of my powersupply it has negative outputs. How does it happen like this?. Any brilliant ideas how to get through with this problem. Thanks so much! Godspeed..

[jdimpas]

Additional info:

*Outputs in my PSU*

Red = -5 DC Volts
Yellow = -11.70 DC Volts
Orange = -3.38 DC Volts
Gray = -0.13 DC Volt
Violet = -5.10 DC Volts
Blue = +10.98 DC Volts
White = +4.54 DC Volts

Seems like inverted... help!

[Harvey]

You've got your leads plugged into your meter the wrong way around?

[jdimpas]

Originally Posted by Harvey

You've got your leads plugged into your meter the wrong way around?

Nope! the leads was connected correctly, in fact i tested other new power supply it has positive outputs. Black probes in the voltmeter was connected to ground of the powersupply(black cable).

[kc8adu]

something up with the color codes?
i dont know of any failure mode that can cause this.
post a pic of this unit.
brand,model,and open covers.

[Wizard]

I have seen this before. Like brown, blue, etc instead of standard black, red yellow, orange etc.

Cheers, Wizard

[Wizard]

I have seen this before. Like brown, blue, etc instead of standard black, red yellow, orange etc.

And what is this power supply from and picture will help.

Cheers, Wizard

[jdimpas]

[jdimpas]

All are properly connected from voltmeter to its test probes. Output seems to be inverted and i got 2 powersupply with same problem.

[linuxguru]

Check the DMM against an AA cell - it's probably wired wrongly internally.

[jdimpas]

actually, what really happen was one of computer in the office suddenly shut off and when i turn it on the computer won't work. I checked this powersupply and i was amazed it got negative outputs, so i decided to replaced new powersupply to this computer and it was working fine. so basically, the problem was the powersupply with negative outputs.

[kc8adu]

looks like a harbor fright meter.bet it is backwards.
the psu in the pic is a gutless wonder.
experiment with it and toss it.not worth repairing and possibly not even safe to use.

[jdimpas]

Originally Posted by kc8adu

looks like a harbor fright meter.bet it is backwards.
the psu in the pic is a gutless wonder.
experiment with it and toss it.not worth repairing and possibly not even safe to use.

I just wondering how does the VDC output goes inverted (negative)? im not quite familiar with this problem. Do you have any technical explanation with this?

[kc8adu]

unless someone swapped the diodes in the psu they dont.
the meter is wrong.or someone played a prank on you.
they would also have to reverse the caps or they would explode.

[jdimpas]

i need someone knows the problem..

[linuxguru]

Why doesn't the dumbfuck just check the DMM against a source with known polarity?

[kc8adu]

i smell a troll.

[Krankshaft]

I would chuck that supply as KC said thats one of those "lets see how many components we can remove until the PSU doesn't work anymore" supplies.

If it was a well designed supply then it would be worth it.

EMI filter don't need it safety caps don't need em.

A jumper wire works just as well NOT!!!

I really wonder how anyone with a conscience could design and sell a supply like this.

I can see the original designer silkscreened the safety components on the board but the beancounters started chopping parts out during the building process.

Look at those tiny descrete diodes for the line rectifier pathetic I'd love to draw the full rated 250 watts the thing would probably go up like a roman candle .

It doesn't look like it even uses an opto isolator they used a transformer for feedback isolation.

[PCBONEZ]

You have the meter leads in the wrong holes.
The bottom hole says "common" - that's ground - that where the black wire goes.

.

[Brian C]

This guy must have used the wrong lead connections. Please refer to the attached picture. Common (black lead) should be at the bottom hole. That's why he reads negative voltages, as the current measurement lead has very low resistance to common.