Precision 670 PSU squeals

[lazychris2000]

I picked up a Precision 670 for cheap off craigslist and found out the power supply squeals something awful when it is plugged in (under load or not). I opened the PSU and found no bad caps, I read about if it is >3 years old, you should recap/replace it (source: https://www.badcaps.net/forum/showpo...9&postcount=3). So, I decided to recap it and see if the squealing stopped. Ordered all the necessary caps and went to soldering. Now, not only is it still squealing, it has gotten a little louder. I am having a hard time determining if it is the big high voltage caps or the transformer(s) below them, but it is definitely coming from that area. I added some pics to show what I am referring to.
I am really trying to avoid buying a new power supply because whenever people see I am in Alaska, they immediately triple the shipping cost and I don't want to spend $50+ on shipping for a $50 power supply . Any help would be most helpful.

[Per Hansson]

Re: Precision 670 PSU squeals

You could try using a plastic straw (Non conductive!!!!!)
Poke it against things inside the PSU and put your ear against the straw, you might be able to pinpoint what it is that makes the noise easier this way...

Disclaimer: Of course be extremely careful when working with live electronics, actually this might be a very bad idea if you don't have experience working with high voltage! (Well, a really bad idea in general actually!)

[lazychris2000]

Re: Precision 670 PSU squeals

I tried using a stethoscope to listen to it, but couldnt get close enough to the components cause it was metal and I didnt want to accidently short something out. Straw is a good idea...I didnt think about that. Will give that a shot tomorrow if I have time.
After accidently shocking my ear when I got too close to something, I am definitely gonna be more careful next time. I work with high voltage stuff alot, but sometimes I get kinda stupid....

[lazychris2000]

Re: Precision 670 PSU squeals

Using a hollow pen (appearently, I have no straws), the noise is loudest coming from the little transformer, which is kind of what I was afraid of. I am a little unsure of where to go from here--is the problem caused by a failing transformer or is something else on the board causing it to squeal? I would hate to go to all the hassle of finding then replacing the transformer (not to mention having to pay like $15 shipping for a 3oz part) if something else is causing problems. Just a note, there are no burn spots or discoloration on the board and all the components appear to be in perfect physical condition.
Transformers are an area in which I am unfamiliar, so maybe someone can help me identify this little guy. On top is DT-E16-126T 8000 DET0422<01>2536A. On the side, printed on the plastic wrapper is MP-1301 E115982. Punching these into google gives me no information at all.

[lazychris2000]

Re: Precision 670 PSU squeals

Taking a measuring tape to a standard ATX power supply I have laying around (550W Rosewill), I am fairly certain that if push comes to shove, I can take out the dell supply and replace it with the power board in the Rosewill then splice in the proprietary dell connectors. The only problem I may run into would be the mounting holes, but that gives me a good reason to use my dremel . Hope it doesnt come down to that, but if it does, it seems like a good contingency plan to me. Only problem I forsee would be the wire labeled Fan_Fail, but that is probably just going to be something I can tie into a ground or +5 or something. Will research further.

[Per Hansson]

Re: Precision 670 PSU squeals

You can try resoldering the transformer
They are heavy and can easily for that reason alone damage the solder so it does not make contact, they also get hot which is another reason the solder can fail

[midibob]

Re: Precision 670 PSU squeals

Hi,

I've known PSU's to squeal due to the caps in the feedback oscillator cct. These are normally 1uF or 4.7uF at about 50v and they are usually situated near a heat sink so they live a hard life. As they dry up they introduce the squeal due to the mis-shapen waveform. Have you checked/changed these at all? A squirt of freezer will usually identify the culprits.

Good luck
Midibob

[lazychris2000]

Re: Precision 670 PSU squeals

Per Hansson: I will give that a shot and see what happens. That is something I had not considered

midibob: I replaced everything 470uF or higher because I didn't have any smaller caps. I will have to order a few once I get a chance to get in there and identify them. I think there are a few of them near that little transformer, so that seems like a good possibility they are squealing.
When you say "a squirt of freezer", do you mean turn a can of compressed air over and hit it with the super cold liquid that comes out? Also, how will I know if I have identified the culprit?

Thank you both for your help!

[lazychris2000]

Re: Precision 670 PSU squeals

So I am pretty sure its dead now for some reason. I pulled it apart to resolder the transformer and find out what caps I would need to order when I found this (check out the pictures). That trace was most definitely not there before and I am not sure where it came from. I have not had it plugged in since I recapped it. Maybe it happened while I was testing it? Either way, it does not fire up at all anymore, and I am pretty sure this is fatal. I considered just using a piece of wire to jump the busted section, but I'm not sure that is really gonna help.
I was hoping to save $150ish on a new psu, but unless anyone has any ideas about what may have caused it or any way to fix it, I guess I have to buy one anyway....
I do appreciate all your help, even tho it turned out to be for nothing

[midibob]

Re: Precision 670 PSU squeals

Hi,

I think it's gone to meet it's maker.
It probably is repairable but it's not something that can be talked through I'm afraid.
I can't see what that track connects to but it's likely it would have been one of the mosfet connections which has probably gone s/cct.
The two optic isolators have gone too and more than likely a zener diode. Even if you repaired all these you might still be back with the 'squeal'

A bit late for this but.....
With regards to using freezer. It only takes a little squirt and if the caps are drying up even a cool blow of compressed air will change their properties enough so you would hear a difference in the frequency of the squeal.
Don't encase the cap in a block of ice though, that's definitely not the way to test them.

Time to bite the bullet methinks.

Midibob

[lazychris2000]

Re: Precision 670 PSU squeals

A week or so ago, I tried putting a piece of wire across the burnt trace and soldering it to the PCB (it wasnt working anyway, so i had nothing to lose...). Still dead.
Thanks for the info on freezing the caps, I will keep that in mind next time I have a squealing PSU.
I think I might just throw it back on craigslist and see if I cant get atleast some of my money back for it. $150ish is a bit more than I want (or can afford) to spend on this thing right now. There are a number of dual 604 boards online, but only the most expensive ones have PCI-e slots on them, which is what compelled me to buy the system in the first place....eh, I guess its better to have found out now there was a problem than a few weeks down the road when it died a violent PSU failing death

[giuliano72]

Re: Precision 670 PSU squeals

hello all,

after reading lazychris2000 topic i think i have the same problem, my precision 670 power supply also squeals after 10 minutes or so, some of the motherboard caps are also bit bloated

funny thing is that when I jumpstart de powerunit without de motherboard (green/black) it does'nt seem the squeel anymore, weird huh???

i hope someone can help me with a good solution?

edit:
is it possible to change it with a precision 650 powersupply, can someone provide me with a 650/670 powersupply pinout list ?

greetz,
Giuliano

[lazychris2000]

Re: Precision 670 PSU squeals

So, everyone online wants to bend me over the table for shipping to AK (Seriously, I am NOT paying $75+ for shipping on a $100 PSU!), so I have been trying to find out if there is an adapter or something I can buy so I can use a standard ATX PSU? I suspect it is a WTX power supply , but I cant seem to find any info about it on google. I was hoping there was just some sort of adapter I can plug into a 600W power supply I have sitting around over here instead of having to resolder everything from the dell one onto the ATX one. Or is this even possible?

Guiliano, your power supply probably only has a problem when it is under load. I would definitely replace the caps on the motherboard, tho, just to make sure they are not part of the problem (and you dont want to risk burning out dual xeons). Not sure about the precision 650 PSU, but I did find that the XPS Gen 5 uses the same power supply, so if you can get one of those, you should be golden.

[stj]

Re: Precision 670 PSU squeals

what test gear do you own?

replace all the caps - specially really small ones,
fix the trace damage,
meter diodes & transistors for shorted pins.

i suspect a small cap failed, made the oscillator shift frequency down into the hearable range and then caused a transistor to overheat or die by running it too slowly so the heat built up.

[lazychris2000]

Re: Precision 670 PSU squeals

BAsically, I have a voltmeter and soldering iron. I can order whatever caps I need, but I have already recapped the entire board and replaced that burnt out trace and the PSU is totally dead now. I will try checking everything for shorts when I get a free afternoon. With just a visual inspection, I didnt see anything shorted (no stray solder or anything like that), but I never thought to take my voltmeter to it.
Thanks for the tip!