problems with a new PSU

I just bought a new PSU for my computer, and it doesn't even work. Is it possible that I am doing something wrong with the way it's hooked up? Is it also possible that a dud would get through inspection and onto the shelves? I ask these questions because I am at a loss as to why this brand-new PSU just won't work. Any advice would be helpful!

 

What kind of PSU is it, what brand / model CPU do you have?

 

If you bought this psu because your previous one din't work either, have you considered the mains supply lead/socket and any fusing they contain.?


Studio T

 

The PSU I purchased is a Spire Power brand one, Pentum IV ATX2.0 Power Supply (if that means anything). It has a switch on the back which, I assume, turns the unit on or off. The PC is a Compaq Presario. The PSU has a fan, and though it SHOULD work once the plug is plugged into the wall, it doesn't. Neither wattage setting makes a difference, as it just doesn't turn on, and not even when I fiddle with the switches. Am I missing something here? I mean, it definitely should turn on once I plug it in, especially once the wires are plugged into the computer's motherboard and hard drive. I spent 95 dollars on this thing and if it's a dud.......ahh! any help would be amazing!

 

You should be glad that the psu won't turn on unless you have it connected right, if you go trying both settings of the voltage selector. That is a very dangerous thing to do. Halo did say CHECK it is set correctly for your mains supply.

Compaqs are particularly fussy about connected power supplies. Did the old one have a white lead or was one of the positions on the main 20/24 pin connector not connected? Does the new supply match this?

Did you check the supply lead as I suggested?


Studio T

 

I'm sorry, I should have clarified, I fiddled with the on/off switch, not the wattage switch. It was set on the correct wattage for the PC. The old PSU did have a white lead. In addition, the new PSU has some connectors that aren't connected because it is larger than the old PSU's connector. I'm assuming that the white lead is the connector that plugs into the motherboard, and it has all the colored-cables leading into it. If that's not it, then if you could explain, that would be awesome. But shouldn't a PSU turn on, even if it's not plugged into the computer, itself? If I'm wrong, then I apologize. But I'd still like to hear your suggestions as to how to get it working.

 

The main connector from the power supply to the motherboard was originally all there was. It was a rectangular connector with 20 connections, all of which were used for something.
As computers consumed more power extra supply leads were added. There are two types.
Firstly an extra connector , straight to the motherboard with 4, 6 or 8 terminations.
Secondly the 20 pin became 24 pin. The extra 4 pins were placed on the end so that the first 20 pins of the new 24 pin plug would still mate with the old 20 pin socket. So you can just plug in new to old (but not the other way round). Sometimes the 4 pin block is detachable.
The white lead was for negative 5 volts which is no longer always used and so was dropped by some suppliers. However I think that Compaq has always required it.

Of the 20 pins one provides what is known as standby power, and comes from a small auxiliary power supply from within the main psu box, so that the motherboard is always partly live so long as the mains (wall) voltage is connected.
Two more pins provide control signals between the power supply and the motherboard. The part of the motherboard that is live monitors one of these signals and if it also receives the signal from the power up button on the front of the computer sends a 'start the main engine' signal back to the power supply.
Note that while all this is happening everything is apparantly dead, no fans are turning or lights are on.
UNLESS THIS SEQUENCE OCCURS AND THE CORRECT SIGNAL IS PASSED BACK TO THE POWER SUPPLY the main psu will not switch on, starting fans etc.

Thus a good psu WILL NOT START UNLESS IT IS CORRECTLY PLUGGED INTO A WORKING MOTHERBOARD OR POWER SUPPLY TESTING EQUIPMENT - PERIOD.

It is difficult to help if you don't answer the questions - they are not trick questions there are many reasons why a pc will not start and I do not know if you bought a new supply because the old one was apparantly dead or for some other reason. If it was apparantly dead, there are many other components which can prevent a pc starting. I am trying to work through the possibilities with you.


Studio T

 

I checked the lead into the motherboard, and it connects correctly into the motherboard. All the power leads connected correctly into the hard drive, cd drive, etc. To answer your question about the old PSU, yes, I did purchase a new one because the old one was apparently dead, as was suggested on this site when I explained the issue my PC was going through. Instead of turning on, the PSU made a high-pitched sound similar to the the ringing in one's ear. So I opted to purchase a new one. The connectors are all connected in their right places, including the main lead into the motherboard, though you are correct, it does have an extra set of pins that don't fit in with the connector on the motherboard. They are left out of the connector, and it is also possible to detach them, as the lead has that capability. Basically, I followed instructions in installing the PSU and to no avail. I assume that it may be because Compaq has a problem accepting "universal" PSUs. If that is the case, then I guess I will call the company and see what I can do. I apologize that I'm not completely computer literate, because I've never taken a computer apart. I know more about software than I do about hardware. In any case, there are a bunch of power leads and connectors that aren't connected to anything, mainly because everything that needs to be connected is already connected, and the rest don't seem to have counterparts on the motherboard. Could that be an issue? I'm sorry if I still haven't answered your questions correctly, but I'm doing the best I can with the little knowledge I have in this. Again, I still am very appreciative of your help.

 

OK I found your earlier post from Mid March, I didn't see that one before.

If you were upgrading from a working psu to a beefier one to supply extra hardware then I would know you power cord was intact. As it is you have a dead pc. I have seen all sorts of damage to power cords, my daughter's rabbit chewed one once. However you say there is a high pitched whine coming from the old psu. This suggests the switching cricuitry is still running within it. The switching is responsible for the noise. However the rectification and regulation circuitry may be shot.

There is the possibility that whatever caused the psu to fail also caused further damage elsewhere in the pc.

Did you get the replacement from a local store or mail order? If it came from a local store try taking both supplies there and asking them to test both.

You haven't said whether the new supply also has the white wire or one unused connector in the 20 pin plug? If it has one unused position it will be of no use as a replacement. I have seen people having problems with Compaq before. Compaq do not always use the standard colours for the connecting wires although the actual positions are standard (unlike some older Dell units). These pcs never seem to work with universal replacement supplies, only Compaq units.

Studio T