Completed Re-Capping of PS: 11.5v on +12v rail too low?

[ran]

First, thanks to everyone for their help and suggestions on replacing caps on my G4 Sawtooth Power Supply (original thread and picshere )

I was able to order all the appropriate caps from Mouser, and have completed the replacement on this Delta DPS-338BB PS.

I jumped the PW_ON and Gnd wires on the motherboard connector and connected 1x120mm, 2x80mm and 1x92mm fans (had them lying around) to run the power supply. However, it would only briefly turn on (fans would start to spin) then turn off again.

I thought perhaps that was not enough load, so I attached a couple of old CDROM drives - and that seemed to do the trick as the power supply is currently running.

My next step was to measure the loads on the +3.3v, +5v, and +12v rails with my multimeter.

The +3.3v was @ 3.3, and the +5 was @ 5.2 (no significant loads on these rails anyway). However, the +12v rail was down to 11.5v, which seems rather low.

Is this an acceptable voltage?

Is there a better way to test whether this power supply is working ok before I put it back into the computer?

Again, thanks for your (collective) help...

Ran

[linuxguru]

Re: Completed Re-Capping of PS: 11.5v on +12v rail too low?

Once you have a sufficient load on +5v, it will drop down maybe 200 mV and +12v will increase by about 500 mV to compensate. These two rails are usually regulated together, with additional cross-regulation provided by the toroidal inductor. The measurements you have are OK.

[trodas]

Re: Completed Re-Capping of PS: 11.5v on +12v rail too low?

No, 11.5V on 12V rail is not acceptable voltage for good PSU, yet you did not provided the PSU load on all rails, so, I say connect it to the machine and then measure again
You are very likely to get much better readings.

And unless the +12V rail is not providing like +17V or such, you can't damage anything, so, go ahead. As already suggested, the balanced load probably can fix the voltage. Small fluctuatios is normal, and most PSUs did not regulate to exact voltages, so I don't shake head at about 200mV shift.

I would care much more about ripple, but then again - measuring ripple with scope on load that it not like the mainboard provide is proven useless again. Been there, did that and then wonder why the ripple is so much better on the board

[Rainbow]

Re: Completed Re-Capping of PS: 11.5v on +12v rail too low?

11.5V is probably OK. Once you connect it back to the system (so it will be properly loaded), the voltages should be OK.

[ran]

Re: Completed Re-Capping of PS: 11.5v on +12v rail too low?

Thanks so much for all your responses. I'll go ahead and hook it up tonight and see what happens!

Beyond measuring voltages, are there other things I can test on this PSU with my lil' ol' multimeter?

[trodas]

Re: Completed Re-Capping of PS: 11.5v on +12v rail too low?

Unfortunately - nope. You need scope to check out the ripple the PSU produce and estiminate then the quality of the PSU (caps is not all, cheap regulation circuits will always produce spikes...)

[gg1978]

Re: Completed Re-Capping of PS: 11.5v on +12v rail too low?

Your Power supply sounds fine.. I suspect the reason your +12V is a bit low, and your +5 is a bit high, is that you have no load on the +3.3V.. All of the good quality ATX power supplies i've seen have the +3.3Vsense line, which lets the power supply know what the actual 3.3V reading is at the board. Since this is an Apple G4 PSU, it's certainly a good PSU..


Also, i've got a 300W Delta that refuses to turn on if there is no load on the +3.3.. Looks your Delta will turn on with no +3.3V load, but regulation may not be optimal.. Try probing your voltages with the power supply in the G4, with at least one HDD and one CDROM drive hooked up.. I think you'll find your +12V will be perfectly in tolerance then.. Even though techically it's within the +/- 5% tolerance band right now..

[ran]

Re: Completed Re-Capping of PS: 11.5v on +12v rail too low?

Your Power supply sounds fine.. I suspect the reason your +12V is a bit low, and your +5 is a bit high, is that you have no load on the +3.3V.. All of the good quality ATX power supplies i've seen have the +3.3Vsense line, which lets the power supply know what the actual 3.3V reading is at the board. Since this is an Apple G4 PSU, it's certainly a good PSU..


Also, i've got a 300W Delta that refuses to turn on if there is no load on the +3.3.. Looks your Delta will turn on with no +3.3V load, but regulation may not be optimal.. Try probing your voltages with the power supply in the G4, with at least one HDD and one CDROM drive hooked up.. I think you'll find your +12V will be perfectly in tolerance then.. Even though techically it's within the +/- 5% tolerance band right now..

Great - I'll do that....as soon as I can find a mac video card!
Thanks for the help, everyone!!!