Dell NPS-250KB caps

[999999999]

Re: Dell NPS-250KB caps

I don't know that it's a rule, but many if not all the smaller Delta's have a stamped out metal grill for the fan. Along these cut edges it may rust eventually, and be sharp enough to cut your finger if you were to run the finger across the cut edge, but that doesn't necessarily make the rust a problem so long as it's not scaling off in big pieces (if the PSU is that bad, I would wonder about the rest of it, if it's even good to redeploy it for another tour of duty).

I agree the Deer should be removed, I'm just not seeing what difference it will make if the fan exhaust grill has a little brown coloring to it, but if you just wanted the quick and easy solution, take a dry paper towel and rub it against the rust to get any loose off, then take some enamel model paint and just paint around the interior cut areas of the exhaust slits.

There is another option. Cut out the hole so it's even less restrictive, then decide whether you need a tubular (chrome, etc.) fan grill on it. I just don't know that this PSU is really worth so much time, you should be able to find a reasonable brand new 200W+ PSU for less than $40 USD. Your local mom-n-pop computer shop might even have some used ones lying around they'd sell for almost nothing. I like Delta PSU but if it's eyecandy/perfect looks you're after, Delta was never a winner there even when the unit was new and rust-free. It's also a little underpowered for many uses these days. Even a good quality PSU has to be seen as only capable of it's stated wattage for moderate term use, and better derated to account for longer life remaing after it is already several years old.

[linuxguru]

Re: Dell NPS-250KB caps

Delta doesn't do shiny anodization and all that bling, but their galvanized sheet steel doesn't rust easily either. It kinda gets rougher and patchier with age as the zinc coating oxidizes, but it still doesn't rust in normal use - YMMV if you're in a moist, salty seaside environment.

Delta also always delivers the rated wattage - if it says 300W, it is 300W and can handle just about any standard server load thrown at it. That's waaaaay better than the 500 - 600W Deers, which are all in reality not capable of delivering more than 135 - 200W max.

I'll second the suggestion to use a Coke bath to get rid of rust - it works even better if the coke is heated in a microwave to 60 - 70c before immersing the rusty parts. The coke used in this manner can't be consumed, though :-( - it smells/tastes decidedly steely (maybe that's how zinc/iron phosphates taste).

For old hobby tinplate restoration, I have used the coke bath, followed by a rinse and then baked the part in an oven. That helps 'fix' the blackish anodization from the coke bath more permanently, delaying future rusting.

[stevo1210]

Re: Dell NPS-250KB caps

I sanded away the rust last week and spray painted silver paint over the rusted areas. Looks good so far.

Only problem is that this PSU makes a hissing/ whining noise when turn on. It's silent in soft-off mode, but when the PC is switched on, it will make a hissing noise that gets annoying after a while.

I have found where the noise is coming from and it's coming from where the primary caps are
Could it be because I didn't reapply the epoxy/ glue to stick the top of the two primary caps to the heatsink next to them??

Thanks.

[999999999]

Re: Dell NPS-250KB caps

The caps have epoxy/glue because they are tall heavy parts and movement could weaken the solder joints. The whining is almost certainly coming from one of the magnetics, a choke or (more likely the) transformer.

[stevo1210]

Re: Dell NPS-250KB caps

I recently replaced the primary caps again. This time I found proper values of 560uf. The new caps are Panasonic 560uf 200V caps. The main reason that I recapped it again was because my PC kept restarting with the 470uf caps.
Only problem now is that even after I replaced the primary caps with original value caps, my PC still restarts when the PSU gets warm.
It's not only one PC I've tried this PSU in, but three different PCs with the same result.

I don't know what's wrong with this Delta PSU, but I am only guessing for now that when I bought it had broken some solder joints somewhere because the PSU originally fell and impacted on something which also bent the PCB....

Anyone have any suggestions to what's wrong with PSU before I have to trash it.... I really don't want to have to trash it because it's a very high quality Delta made PSU.

Thanks.

[Super Nade]

Re: Dell NPS-250KB caps

Maybe you need to be looking at the secondary side..

[starfury1]

Re: Dell NPS-250KB caps

Think you may have already been through the following but

if you haven't already stevo recap the secondary and reflow (resolder) all the main type components such as the transformers, power devices on the heatsinks.
(makes sure you don't bridge anything while doing this, take a few photos of the pcb for reference just incase)

A good visual you might pick up a bad joint but the shot gun method above probably wont hurt.
Jewels loupe mag glass and good light is very helpful.

The whining maybe a sign of stress from what appears to be a heat related fault
its possible its some what normal and you being young just have good ears.
(if you don't plug em with an ipod for 10 hrs a day )


If that don't solve it, then you are probably in for some real detective work I guess.

Components can fail while under stress but show no signs of it cold or from static tests.

HTH

Cheers

[999999999]

Re: Dell NPS-250KB caps

If your primary caps were defective, yes they should be replaced. Otherwise, 470uF (x2) is enough for a ~ 250W PSU.

You wrote that it happens when it gets warm, so I would suspect inadequate chassis airflow.

[ChaoZ]

Re: Dell NPS-250KB caps

WHen your system restarts... what does it do? Can you describe?

- system restarts by itself from windows ?
- system BSOD, does memory dump and restarts ?
- system shutdown by itself ?

do you think you might be at the wrong side of the problem?

cheers

[stevo1210]

Re: Dell NPS-250KB caps

WHen your system restarts... what does it do? Can you describe?

- system restarts by itself from windows ?
- system BSOD, does memory dump and restarts ?
- system shutdown by itself ?

do you think you might be at the wrong side of the problem?

cheers

The System(s) just restart automatically in Windows. No BSODs or memory dumps.... nothing.
The screen just suddenly goes black and then I see the system going through POST again. When Windows boots up, it's as if nothing ever happened. No error messages.... nothing.

I've tried this PSU on three different PCs and the effect is the same, every single PC restarts after about 30 minutes or whenever the PSU gets warm. I've checked the fan and it's still spinning. The PCs are all properly cooled with exhaust fans etc.

I also tried a DEER PSU with all three systems and I don't get any BSODs even after hours of use.

I think that I may have a broken solder joint somewhere in that PSU. This PSU is in my fathers PC and he's not very happy at what's happening at the moment with the PC restarting after a while.
At the moment, he's using a PIII until I can fix this PSU which is currently powering a Celeron 2Ghz PC.


Thanks.

[ChaoZ]

Re: Dell NPS-250KB caps

Perhaps the voltage is too low after the repair, check your +5, +12V rails.

I have a delta as well, they can be tuned via one of the POTS.

[larrymoencurly]

Re: Dell NPS-250KB caps

Perhaps the voltage is too low after the repair, check your +5, +12V rails.

I have a Delta as well, they can be tuned via one of the POTS.

Another problem with some older Deltas is that they won't put out enough voltage unless the load is high enough. I have a couple of 300W DPS-300 Deltas that won't put out enough voltage on the +12V rail to let the HD spin unless at least 3-5 amps is drawn from the +5V rail.

[Brian C]

Re: Dell NPS-250KB caps

The Cross Regulation effect is usually worse on the +12V output, depends on the design of secondary control feedback. The +3.3V rail on the other hand, uses saturable reactor control method which provides better regulation and higher efficiency.

[999999999]

Re: Dell NPS-250KB caps

Lots of fairly aged designs regulated based on 5V rail but how often would you pair such a PSU up with a system not even using 3A @ 5V?

If the intended use is this unusual I wonder if there's a better alternative or you could always try to hack the feedback circuit to regulate based on 12V instead of 5V, providing the subcircuit is staightforward or if a proprietary controller IC then you have the datasheet or pinouts.