Bad negative -12V Power Supply line

[KillerBee]

Yesterday my 2 year old Raidmax RX-530SS Power Supply went bad
First could smell something burning and then computer shutdown

Tried to restart:
P/S fan works and blue LED light work
computer CPU and case fans work
DVD opens and closes
but get no POST,beeps or any display

swapped video card and monitor - same problem
unplugged both hard drives - same problem
(no other extra cards installed)

Unfortunately don't have another ATX2 P/S handy to swap in for testing
So measuring voltages:
+5V is good at +5V
+3.3V = 3V
+12V = 11V
-12V = -6V

I always figured the -12V used the +12V line but with a reverse connection. Is it really using a separate component?

 

[VirtualLarry]

Unfortunately, the likelihood is good that the PSU burned out and took the mobo with it.

Test your rig with a known-good PSU to make sure.

In the future, do not use Raidmax PSUs. They are junk.

 

[KillerBee]

Thanks for the quick reply -

Actually it's only been 1 year and 11 months
and came with a 2 year warranty
http://www.newegg.com/Product/Produc...82E16817152028
so I've emailed Raidmax and waiting to hear back from them on it.

but mainly wanted to find out if anyone knows about the -12V components
and if they are separate or not from the +12V components?

Edit: NoScript or ABP always causes the Detonator links to fail for me
so search the newegg site for: N82E16817152028 for the exact part

 

[KillerBee]

Well Raidmax gave me an RMA for it :thumbsup:
but I have to pay shipping :thumbsdown:
which will cost $16 to send it to them (east coast to west coast)

or I can spend an extra $2 and get this Corsair CX430
http://forums.anandtech.com/showthread.php?t=2184481
and be up and running quicker
(hopefully the rest of my computer wasn't harmed)

Learning alot about power supplies since it went down.
Decided to go with the Corsair ...yes I have a limited budget
but at least it passed jonnyguru tests
http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story4&reid=214

 

[greenhawk]

I always figured the -12V used the +12V line but with a reverse connection. Is it really using a separate component?

It use to be separate wirings on the transformer, but for a long while now nothing has needed the negitive voltage (just serial and printer ports), but even those ones are fading fast / have a low need for post people.

Currently powersupplies I suspect are using DC-DC converter IC's for the job as current is generally very low depand (if used at all).

I can not remember the specs for RS-232 off the top of my head, but as long as the negitive is < -3V, it should still work fine for RS-232 communications. Only issue is if you want that voltage to power a attached serial device (unlikly).

 

[WhoBeDaPlaya]

Stay clear from Raidmax, Powmax, Coolmax, Diablotek, etc. crapola power supplies.
The 430CX would be a far better investment of your money.

 

[KillerBee]

hmmm...after reading your explanation I'm now gettin worried the Raidmax may have fried something else like VirtualLarry predicted :'(

Will soon find out when the corsair arrives - hopefully tomorrow

 

[punker]

It use to be separate wirings on the transformer, but for a long while now nothing has needed the negitive voltage (just serial and printer ports), but even those ones are fading fast / have a low need for post people.

Currently powersupplies I suspect are using DC-DC converter IC's for the job as current is generally very low depand (if used at all).

I can not remember the specs for RS-232 off the top of my head, but as long as the negitive is < -3V, it should still work fine for RS-232 communications. Only issue is if you want that voltage to power a attached serial device (unlikly).

not really my Xeon server has a serial port and and ps/2 ports

 

[KillerBee]

Woohoo - everything survived

Voltages reading much better too with the new Corsair :
5V = 5V
3.3V = 3.3V
12V = 12V
-12V = -12V

 

[Mark R]

I can not remember the specs for RS-232 off the top of my head, but as long as the negitive is < -3V, it should still work fine for RS-232 communications. Only issue is if you want that voltage to power a attached serial device (unlikly).

For a long time now, most PCs have used 5V serial comms, with a monolithic RS232 converter chip. These RS232 voltage converter chips don't need a -12 V supply - they run on 5V and include their own internal DC-DC converter (for both +12 and -12 V) supplies.

An interesting property of these voltage converter chips is that they accept logic-level inputs (so 0V is detected as a 0, and 5V is detected as a 1), whereas the traditional RS232 chips insisted on a clear negative voltage for a 0.

 

[Modelworks]

For a long time now, most PCs have used 5V serial comms, with a monolithic RS232 converter chip. These RS232 voltage converter chips don't need a -12 V supply - they run on 5V and include their own internal DC-DC converter (for both +12 and -12 V) supplies.

An interesting property of these voltage converter chips is that they accept logic-level inputs (so 0V is detected as a 0, and 5V is detected as a 1), whereas the traditional RS232 chips insisted on a clear negative voltage for a 0.

The MAX232 is probably the most well known one. Another bonus of this chip is it is great for generating a negative voltage on projects that use things like opamps when you only have a single supply and need a low current - rail.

 

[mariolino]

Hey, I have had a negative 12V (-12V) line failure in my PSU as well it's an old Antec Truepower Trio. I have a dedicated PSU tester which tells me exactly which lines are faulty, and the -12V is really bad. As in, the voltage is negative but undefined (fails to settle to any specific value).

Now, reading this thread, one would come to the conclusion that the -12V line is not much use nowadays. Then I wonder why did my PC stopped working? This line must be doing something important - as also evidenced by the OP.

So my question is: what does the -12V do that is so important to the motherboard's function?



(Sorry for doing this, I know some consider bad form to resurrect old threads, but if there aren't newer ones, then I have to do what I have to do.)

 

[Harvey]

So my question is: what does the -12V do that is so important to the motherboard's function?

Check the specs for your motherboard. If it requires -12 volts, it won't work without it.

 

[mariolino]

Check the specs for your motherboard. If it requires -12 volts, it won't work without it.

That's circular logic.

 

[Harvey]

That's circular logic.

No, it's not. Most newer motherboards don't use the -12 volt rail so most newer supplies don't include them. If his motherboard is old enough to require it, it won't work with a supply that doesn't include it.

 

[mariolino]

It was hardly worth it to register an account on Anandtech to get such a banal answer.

 

[Harvey]

It was hardly worth it to register an account on Anandtech to get such a banal answer.

It was a simple answer, but I just checked this Wikipedia page about the ATX power connector, and I was mistakenly thinking about the -5 volt rail, which has been removed from the spec.

The ATX specification requires the power supply to produce three main outputs, +3.3 V, +5 V and +12 V. Low-power &#8722;12 V and 5 VSB (standby) supplies are also required. A &#8722;5 V output was originally required because it was supplied on the ISA bus, but it became obsolete with the removal of the ISA bus in modern PCs and has been removed in later versions of the ATX standard.

Sorry if I caused any confusion.

 

[mariolino]

It was a simple answer, but I just checked this Wikipedia page about the ATX power connector, and I was mistakenly thinking about the -5 volt rail, which has been removed from the spec.
Sorry if I caused any confusion.

Well, that doesn't really answer the question, but it is new info: I had no idea the ISA bus needed -5V, even though I'm old enough to remember it.