NPS-305CB from Dell Dimension 5000 "dead"

[RG34]

The SMPS NPS-305CB from my Dell Dimension 5000 PC is "dead". I suspect a faulty start resistor and need advice on how to identify this resistor on the power supply circuit board(s). I suspect the resistor because the PC was unplugged from the mains supply while I was away on holiday and now cannot be turned on. Previously there were no problems turning the PC off via Windows and turning it on via the front cover start button. All of the power supply capacitors look in excellent condition, the mains fuse is OK and there is no sign of any damage to the power supply unit. Regards, Richard

[stj]

Re: NPS-305CB from Dell Dimension 5000 "dead"

foto's pls.

[RG34]

Re: NPS-305CB from Dell Dimension 5000 "dead"

Here are various views of the controller circuit board and the mains input circuit board:






Regards, Richard

[ben7]

Re: NPS-305CB from Dell Dimension 5000 "dead"

Is it me or are some of the Ltec caps bulged slightly?

My guess is that there is a bad capacitor or two somewhere.
The PSU won't start because faulty electrolytic caps will have high ESR when cool, and it will be lower when hot/warm.

You could try heating the board with a hair dryer to see if it will start working again. Just make sure not to get it too hot, or you'll pop the capacitors XD (Though, they have to get over 100C to make them pop on you...)

Commonly it's the little electrolytic caps that go bad and cause this.

But yes, it certainly could be caused by something else.
Just, seeing the Ltec caps in there makes me suspicious that one might be bad.

-Ben

[Wester547]

Re: NPS-305CB from Dell Dimension 5000 "dead"

Doing a might bit of research, the NPS-305CB is a unit that has a fan at the intake rather than at the exhaust, and possibly a PPFC. So those capacitors might have been under a bit of thermal duress. The primary CapXons and LTEC capacitors are indeed suspect, but more so the smaller, GP ones as Ben said. Those smaller LTECs, akin to the smaller Teapos, have a penchant for silently drying out over time. Are you getting +5VSB? Do you have a digital multimeter or ESR meter? You'll need certain tools to check the secondary rectifiers and bridge rectifier for shorts (and the other primary components), the condition of the capacitors, etc. I don't think those LTEC are bulging. If even a bit of hydrogen gas was present inside, there would be slightly more pressure at the top (or bottom). That doesn't mean they can't be bad without showing it, though. Also, "bad" capacitors could bloat under 100*C.

[RG34]

Re: NPS-305CB from Dell Dimension 5000 "dead"

Gentlemen, I appreciate your comments and may investigate the capacitors further.

However, before I dismantled the psu, I tried to get it to start up by shorting pin 16 of the 24-pin ATX mother board power supply connector (green power on) to an adjacent ground pin; result nothing and even the fan didn't run.

Meanwhile, can any of you comment on the start resistor - does the NPS-305CB use this method to start from scratch (not standby)? Prior to going on holiday, I had no start up problems with this computer which had previously not been disconnected from the mains supply for a very long time.

Regards, Richard

[RG34]

Re: NPS-305CB from Dell Dimension 5000 "dead"

...... and, if I can eliminate the start resistor (if any), I'll get myself an ESR meter and check out the capacitors.....RG34

[stj]

Re: NPS-305CB from Dell Dimension 5000 "dead"

there are 2 power supplies in the case, the main and the standby.
the standby must work or it cant start the main.

and it's not a startup resistor, those have not really been used for years.
it's a startup capacitor - usually between 10 and 100uf

[RG34]

Re: NPS-305CB from Dell Dimension 5000 "dead"

...yes, but for an SMPS that has no mains on/off switch, isn't there a resistor (around 500kohm) that initially trickle charges the start capacitor when the mains supply is first connected and so enables the control circuit to be able to detect the use of the start button? At all other times the PSU is in standby even though the PC is off?

[stj]

Re: NPS-305CB from Dell Dimension 5000 "dead"

yes, and no.
there are still 2 supply's - one is on soon as you connect the power.

they usually bleed power through several resistors, and the circuit is much more reliable than those things used to be in the old days.

i remember the days of replacing degraded resistors that couldnt handle the voltage, but these days it's not a problem you find.
99% of the time it's a bad cap or shorted protection diode.

[momaka]

Re: NPS-305CB from Dell Dimension 5000 "dead"

Looks like the output wires have standard colors... so, see if there is 5V present between the purple wire (5 VSB rail) and any black wire (ground). If you don't have a multimeter, you can use a small 12 V, 10-15 Watt halogen bulb (like MR16, for example) to see if it lights up (in which case, if it does, it means the 5 VSB is likely working).

Your computer will not start if the 5 VSB rail is not present.

[RG34]

Re: NPS-305CB from Dell Dimension 5000 "dead"

Many thanks all for your comments.

1. Following the suggestions of Wester547 and Momaka, I checked +5V SB (pin 9) and found +5.05v (also found +4.68v on "power on" (pin 16)). So as it seemed to me that the SMPS might now be OK, I reconnected the dismantled psu to the mobo etc. and the PC powered up! I'll now reassemble the circuit boards and fan back into the psu housing, refit in the PC tower cabinet and see if my luck continues....

2. STJ - you refer to the "old days"; how far back is that? My Dell PC was built in November 2006. If things go wrong again I might still need advice on finding a start resistor :-)

3. Ben7/Wester547 - I'll reserve the hairdryer for a future investigation if the psu appears to fail again. I checked all the capacitors and found no bulges.

Regards, Richard

[stj]

Re: NPS-305CB from Dell Dimension 5000 "dead"

old days = pre 2000.
when psu ic's needed more current and the resistors werent surface-mount.

infact that last bit is the key, standard carbon resistors arent rated to run at 300-400v.

[momaka]

Re: NPS-305CB from Dell Dimension 5000 "dead"

1. Following the suggestions of Wester547 and Momaka, I checked +5V SB (pin 9) and found +5.05v (also found +4.68v on "power on" (pin 16)). So as it seemed to me that the SMPS might now be OK, I reconnected the dismantled psu to the mobo etc. and the PC powered up! I'll now reassemble the circuit boards and fan back into the psu housing, refit in the PC tower cabinet and see if my luck continues....

That's a poor practice. Problems rarely go away or magically fix themselves.

You should have at least recapped the LTec caps on the 5 VSB circuit. Ben7 is correct - the tall LZG does appear to be bulging a slight bit in the picture. And even if it isn't, it is still good to replace it with something reliable, because cheap cap brands regularly fail on the 5 VSB rail.

[RG34]

Re: NPS-305CB from Dell Dimension 5000 "dead"

Yes momaka you are right, right, right!

However, as ever, it's a matter of priorities; I'm making the 2006 Dell Dimension 5000 redundant and just need it to stay alive with minimum effort for about 1 week whilst I extract data from it.

Nevertheless, I'm tempted to explore the SMPS problem(s) further and subsequently may well analyse the psu and practice replacing various capacitors. So what brand of capacitor should I buy here in UK in place of the, allegedly crappy, Ltec brand? BTW, here's a photo of the capacitors which I think you referred to as associated with the 5VSB line:



I can't see that any are blown.

Regards, Richard
PS Is it OK to scrape away the bits of white gunge that's splattered over various components of the psu? What's the purpose of this stuff?

[stj]

Re: NPS-305CB from Dell Dimension 5000 "dead"

panasonic FR series.

[momaka]

Re: NPS-305CB from Dell Dimension 5000 "dead"

However, as ever, it's a matter of priorities; I'm making the 2006 Dell Dimension 5000 redundant and just need it to stay alive with minimum effort for about 1 week whilst I extract data from it.

I see.
In that case, don't wait too long to back up the data.

So what brand of capacitor should I buy here in UK in place of the, allegedly crappy, Ltec brand?

Nichicon: PW, PS, PM, PV, PJ, HE, HD, HW
United Chemicon / UCC: KY, KZE, LXV, LXY, LXZ, KMY, KZH, KZM
Panasonic: FC, FK, FR, FM
Rubycon: ZL

I think that is a good amount of choices there. The ones in bold are the closest in specs to Ltec LZG.

BTW, here's a photo of the capacitors which I think you referred to as associated with the 5VSB line:

Nope. The caps for the 5 VSB line are right in the center of pictures 2 and 3 in post #3 above. Near the yellow transformers in the middle.

PS Is it OK to scrape away the bits of white gunge that's splattered over various components of the psu? What's the purpose of this stuff?

Yes, you can remove it if it's in the way.
It's glue to hold down the components when the PSU was manufactured.

[TELVM]

Re: NPS-305CB from Dell Dimension 5000 "dead"



^ I think those four caps at least are on the standby circuit. The IC marked 1200P60 is the standby PWM controller. The '3' and '4' Ltecs are the +5VSB output filtering caps, replace them as per Momaka above. For '1' and '2' I believe you can use any decent 105C general purpose caps of same uF and equal or higher voltage rating.

Momaka will correct me if I'm wrong.

[stj]

Re: NPS-305CB from Dell Dimension 5000 "dead"

i wouldnt risk it, specially 2.
if you dont know the frequency of the ripple then you should go low-esr.

1 is probably your startup cap for the standby supply btw - look at how the bastards put it next to a heatsink! i'm sure they do that shit on purpose.

[RG34]

Re: NPS-305CB from Dell Dimension 5000 "dead"

Thanks TELVM for labelling my psu photo so beautifully and informatively!

Originally quoted by stj: 1 is probably your startup cap for the standby supply btw - look at how the bastards put it next to a heatsink! i'm sure they do that shit on purpose.

Probably not on purpose, that would require some forethought; more likely poor layout design or time pressure to get the design to market :-)

Richard