Dell Precision 470 Workstation

[Toasty]

Re: Dell Precision 470 Workstation

...
- The rule about reducing uF when you lower ESR does not apply to other parts of a motherboard.
[That rule wasn't 'invented' out of the blue, it comes from a tech doc about VRM's.]...

Could you post that or provide a link? Enjoy a good read.

[PCBONEZ]

Re: Dell Precision 470 Workstation

So where is the lytics to poly conversion chart?

There isn't one because too much is involved.

But you are welcomed to do the math [for each cap] if you want to.
Here's a start.
.


.
I'm of course just teasing.
The point is that it isn't that simple.

.
There is a thumb-rule used for VRM caps derived from that math and an engineering document for a VRM MOSFET Controller chip that says if you switch to ploy then you can reduce uF by half. That doc clearly pointed out that in VRM's the ESR is more important than the uF.
-
The thumb-rule isn't that safe to use anymore because it was based on the characteristic of the polys that existed at the time. Since it was created more kinds of polymer have come on the market and some actually have worse ESR than the better lytics.

.

[bigcape]

Re: Dell Precision 470 Workstation

First crack it open .

I see a Thermister NTC1 is cracked. Looks like it let a little "bang-poof" onto the white plastic shielded card. The rest looks fine.

can just that one varible resistor be enough?

Im going to take off that big peice of copper to take a peek at the mack-daddy cap of them all! first im going to find my bleeder resistor

[PCBONEZ]

Re: Dell Precision 470 Workstation

Could you post that or provide a link? Enjoy a good read.

KC8 posted it like 3? 4? years ago.
Always takes me forever to find it but I'll look for a few before I crash for the night.

[bigcape]

Re: Dell Precision 470 Workstation

PCBONEZ,

Whats this 12VA, 12VB, 12VC stuff? I understand the others

[PCBONEZ]

Re: Dell Precision 470 Workstation

Could you post that or provide a link? Enjoy a good read.

Here's the thread:
https://www.badcaps.net/forum/showth...&highlight=mod

Here's the document:


See page 15.

[PCBONEZ]

Re: Dell Precision 470 Workstation

PCBONEZ,

Whats this 12VA, 12VB, 12VC stuff? I understand the others

You have three +12v rails numbered A, B and C.

[bigcape]

Re: Dell Precision 470 Workstation

You have three +12v rails numbered A, B and C.

Ah thank you! Did you see my post about the thyristor above?

[PCBONEZ]

Re: Dell Precision 470 Workstation

I see a Thermister NTC1 is cracked. Looks like it let a little "bang-poof" onto the white plastic shielded card. The rest looks fine.

can just that one varible resistor be enough?

Im going to take off that big peice of copper to take a peek at the mack-daddy cap of them all! first im going to find my bleeder resistor

Thermistors are used as inrush-current limiting devices in PSU.
You probably had a good strong power surge at some point.
It may have thrown setpoints off or toasted other parts like the controller chips.
Certainly the PSU could have had bad voltages and that fried your caps.
.

[bigcape]

Re: Dell Precision 470 Workstation

Thermistors are used as inrush-current limiting devices in PSU.
You probably had a good strong power surge at some point.
It may have thrown setpoints off or toasted other parts like the controller chips.
Certainly the PSU could have had bad voltages and that fried your caps.
.

The system was hooked up to a ups so it had to be PSU side then. They sure did put a lot of white goop in thi thing. That stuff alone looks like bad air flow in itself.

Here is a pic

[michaelahess]

Re: Dell Precision 470 Workstation

So I just came across an old 470, caps were all blown to crap. I ordered a cap set from the CapKing and went to work on it yesterday.

Originally I got an error about the VRM being faulty. If I pulled the second CPU and it's VRM, I got an error about the other VRM being faulty but the system would power up (at least 12v side) and the fans would go crazy.

After re-capping, nothing, I get a solid B light showing a power supply issue. I know that isn't the case as the power supply already fired up, unless the 3.3v or 5v are dead.

I did have two issues putting the new caps in, two of them just wouldn't go through the holes smoothly so I left the iron on them a bit too long I think, they were hot but not HOT, however I did smell a smell I've never smelt before, acrid, I think I may have burned one of the caps.

Any thoughts on what I can try? I don't want to drop any more cash into this so I'm probably going to trash it unless someone has any ideas. Thanks!

[69ragtop]

Re: Dell Precision 470 Workstation

So I just came across an old 470, caps were all blown to crap. I ordered a cap set from the CapKing and went to work on it yesterday.

Originally I got an error about the VRM being faulty. If I pulled the second CPU and it's VRM, I got an error about the other VRM being faulty but the system would power up (at least 12v side) and the fans would go crazy.

After re-capping, nothing, I get a solid B light showing a power supply issue. I know that isn't the case as the power supply already fired up, unless the 3.3v or 5v are dead.

I did have two issues putting the new caps in, two of them just wouldn't go through the holes smoothly so I left the iron on them a bit too long I think, they were hot but not HOT, however I did smell a smell I've never smelt before, acrid, I think I may have burned one of the caps.

Any thoughts on what I can try? I don't want to drop any more cash into this so I'm probably going to trash it unless someone has any ideas. Thanks!

Did you ever resolve the issue? I have a similar machine. With one PS, I get green/amber/amber/off which indicates VRM0. It is a single processor. When trying another PS I see off/amber/off/off (i.e. solid B light). However, both power supplies will power a different 470 with no issues.

[michaelahess]

Re: Dell Precision 470 Workstation

Did you ever resolve the issue? I have a similar machine. With one PS, I get green/amber/amber/off which indicates VRM0. It is a single processor. When trying another PS I see off/amber/off/off (i.e. solid B light). However, both power supplies will power a different 470 with no issues.

I tried and failed, didn't try again, figured I was only out 7 bucks or so, didn't want to make it more!

[69ragtop]

Re: Dell Precision 470 Workstation

Thanks for the reply michaelahess.

Does anyone have directions on testing the power supply? (what voltages on what pins, etc)?

[jrm000kc]

Re: Dell Precision 470 Workstation

I have a 470 I purchased from where I used to work. I replaced the useless video card with an NVidia GT 450 and the performance has been exceptional on the newest games out there. She's been a nice PC.
However, last week I shut it down and my wife heard a buzz of electronic death and a burning smell. I took out the power supply (which no retailer has) and I also have a blown NTC1 thermistor. After reading this thread it serves as an inrush limiter correct? It's the only thing I see fried on the circuitboard. I suspect the cheap carpet in my pad is the culprit. The twin fans were completely filled with carpet fiber dust so I'm thinking a static charge might have killed it. I blew out vast amounts of dust with canned air. My question is since a new power supply costs $150 can I solder in a new thermistor? Or is a blown ntc thermistor a sign of bigger problems? If anyone could show me where I can buy a replacement thermistor and what type and value it is I'd greatly appreciate it. Right now I'm using my other PC, a Dell Dimension 4600 I bought nearly ten years ago and have maxed out memory wise and with a Radeon HD 3650-this thing is glacially slow compared to my 470-I want my 470 back!!!

[kc8adu]

Re: Dell Precision 470 Workstation

ntc sometimes fail.most are killed by something else.check the bridge,choppers,ect.

[jrm000kc]

Re: Dell Precision 470 Workstation

This is my first time attempting to repair a circuitboard. Bridge and choppers are Greek to me. Finding a schematic is like finding hen's teeth-even on the internet.
A guy told me yesterday that snipping out the bad thermistor and replacing the fuse should make it work-unless there's other problems. I'd just replace it but they cost at least $150-and countless companies are throwing them out right now. I guess I'll find a computer surplus/recycling company. These 470's are getting replaced right now so it shouldn't be that hard to find an old one. (I hope.)

[jrm000kc]

Re: Dell Precision 470 Workstation

I've given up trying to repair it. What's a good online site that sells these?

[Toasty]

Re: Dell Precision 470 Workstation

No schematics - proprietary information.
Bridge = bridge rectifier = converts AC to DC
Choppers = switchers = MOSFETs that switch or "chop" the power to the circuit to make an SMPS work.

Prices online vary from $150 to $200 +. Confirm this is a DPS-550DB A.

If you want to consider a repair, we can talk. The killer is the shipping. Probably $15-$20 each way.

T

[kc8adu]

Re: Dell Precision 470 Workstation

yes thats a heavy one iirc.last one i had here had open lytics(450v)in the pfc.the mosfet was shorted and ntc splattered.if it has the samwha 450v caps replace them.