PSU modification - gone wrong!

PSUs: The source of DC power for all components in the PC & often a big noise source.

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BarCodeBlack
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Location: Barcelona

PSU modification - gone wrong!

Post by BarCodeBlack » Sat Jun 14, 2003 3:12 pm

Hi all,

Looks like I may have gone and buggered up my PSU in an attempt to service, clean and quieten it a little. The PSU is a PowerMan FS250-60GTA (250W, sufficient to power the linux box it was installed in!)

I guess you're wondering what I did, and I'm wondering the same as what I did was simple enough 'not' to feck the thing up. Following the removal of the original fan which involved sniping the two leads (red and black) I replaced it with an 80mm Pabst and connected the leads of the Pabst to the original leads using the weird scotch connectors I had purchased from PCSilent.de.

Now whenever I connect the PSU to the mains (this is without physical installation inside the case) and power on, the fan will spin momentarily and then spin down, and remain motionless unless I power down and repeat the process again.

Assuming that all electronic parts are still in working order, the only thing I can assume may be causing the problem is the removal of the 'RPMsense' lead from the fan, as this wouldn't be utilised within the PSU. Anyone aware of fans not functioning correctly without the RPM sense lead?

I'm baffled! Hope someone will be able to shed some light on this matter, as I can´t afford anymore Zalman 300APF's as I've bought enough already this month!!!

Thankyou in advance all

dukla2000
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Post by dukla2000 » Sat Jun 14, 2003 4:03 pm

Best guess is the psu has a noise-killer circuit, that is lowering the voltage to the fan below what it will spin at. Shouldn't be a problem once you load the psu.

Next best guess is the psu is not happy running with no load: plug a hdd into a molex so at least there is some load on the psu.

Last (weak, but worth mentioning) guess: That fan has an rpm sense wire if I understand you correctly? That should be white, the fan -ve is blue (or at least they are on my Papst /2) - check you connected the correct wire to ground and the connectors are firm.

HadroLepton
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Post by HadroLepton » Sat Jun 14, 2003 4:08 pm

BarCodeBlack you said without physical installation inside the case. what exactly do you have connected and what not? did you just plug the main power cord and startet the psu by connecting the green and a black wire from the atx connector?

i have an enermax (don't know which model exactly but a few years old) which does the same thing as you described when i start it using the connect-green-black-wire-method. the fan will start spinning and then stop. but if i plug it to a motherboard it will start just fine. i don't know why this is, maybe they thought that to prevent failures and such the psu will not start when it doesn't sense any power being pulled on the other wires.

other atx psu that i have all start fine using the connect-green-black-wire-method. it's just that one enermax with this behaviour

MikeC
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Post by MikeC » Sat Jun 14, 2003 4:54 pm

dukla2000 wrote:Best guess is the psu has a noise-killer circuit, that is lowering the voltage to the fan below what it will spin at. Shouldn't be a problem once you load the psu.
This is the most likely reason. Try hooking up the mobo/system -- see if the system runs.
Next best guess is the psu is not happy running with no load: plug a hdd into a molex so at least there is some load on the psu.
Another alternative to my advice above.
Last (weak, but worth mentioning) guess: That fan has an rpm sense wire if I understand you correctly? That should be white, the fan -ve is blue (or at least they are on my Papst /2) - check you connected the correct wire to ground and the connectors are firm.
The fan would not spin at all if the incorrect wires were connected, so this is not it.

BarCodeBlack
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Location: Barcelona

Post by BarCodeBlack » Sun Jun 15, 2003 4:20 am

Thanks to all for the rapid response.

In answer to everyones post the answer would have to be yes! The only method used to test the PSU following the modification was the connect green and black wires method. No other devices had been attached to create a load. As one other post already mentioned, the PSU, although simple, old and probably cheap does include the noise-killer circuitry and this may be preventing the PSU from powering up normally.

I just happen to be transferring some devices into another box at the moment, and will take a moment to attach a motherboard and harddrive to the PSU to test once again. Following your replies, I have all confidence the it will function as normal once a true voltage load is forced on the PSU.

I'll get back to you if the problem persists. Thanks all once again.

madlee
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Post by madlee » Sun Jun 29, 2003 1:18 am

hey dude,

I swapped the fan in my Power Man model HP-D301GF5 and I had a very similar problem too.

I could run the power supply after modding the fan with the cover off.

I had nothing hooked up to the PSU, and just switched it on by grounding the PS/On green wire...

It didn't shut off until I tried to reassemble the case by putting the cover on it.

What ended up being the solution was that the 4 screws fastening the circuit board to the case were of two types.. I had 3 pan head screws and one counter sink (flat undercut).

It appears that the flat screw was supposed to go into a certain hole that made contact with a tab from the cover. I had had a pan head in that hole which was making contact. I don't understand why that would have an effect, but after swapping the screws the PSU has operated with no problems..

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