Two different Dells with the same problem

[lonwinters]

I tried to keep it to a minimum, but this post has a lot of detail.

I have a two Dells -
1. XPS 420, Q6600, from 2007
2. Slim Line 540s, Q8399, from 2009

This part applies to both computers:
1. Neither will power on at all
2. The 420 showed signs of impending PSU failure prior to poofing - self reboots. The 540 did not
3. Both passed the manual multimeter power supply test - fan came on and all voltages at all active pins on the 24 pin connector are correct.

QUESTION 1: Is this a comprehensive test for the PSU? I've read that one of the other connectors must also be tested for voltage.
QUESTION 2: Are the other connectors from the PSU (such as the power to the HDD's) inactive until the PC passes POST?


My research yielded conflicting info, but the same general message: Bad motherboard, bad switch assembly, or bad front panel I/O assembly. Information overload and unclear terminology. "Computer won't boot" could mean different things, different points of the entire process, and often is not specified in postsJust weird that both machines have the same problem, within weeks of each other. But, for now, I'm just focusing on the 420 as things are easier to ge to. Here's what I see now:

1. Continuity check of connector coming from front panel shows the switch itself works.
2. There is an LED on the motherboard that lights and stays on
3. Another weird thing. That connector appears to have pin holes, but so does the corresponding port/connector on the MB. No pins anywhere to be found.

QUESTION 3: Is it possible the pins all came off when I disconnected this connector from the MB? There are no traces of pins or evidence they ever existed - 0r that it somehow doesnt use pins at all?
QUESTION 4: Where might I find a diagram that tells me what the other pins are for on this connector an what do I test for? The manual does not supply this info. (If I could determine which pins on the MB side were for the switch, I could jump those).
QUESTION 5: There were other "solutions" I came across, but the just didn't seem likely. Clearing the CMOS by jumper or removing the batter, replacing the bettery itself, or cooking the video card (reflow). Also something about the ribbon cable.

Sorry for all this detail - anyone kind enough to help out, please don't feel obligated to tackle all the questions. Amy input is appreciated. And I am aware that I really just need a new computer but just can't afford it now. I've always had better longevity with Dell's - I'm using a Pentium D tower now, and it's been going strong for over a decade.

 

[C12Friedman]

QUESTION 1: Is this a comprehensive test for the PSU? I've read that one of the other connectors must also be tested for voltage.
A: No it is not, using a multi-meter to measure the voltages of the PSU tells us nothing about it's operation (or lack thereof) under load. To properly test a PSU, some somewhat expensive equipment that can pull a current load and measure it is required.
QUESTION 2: Are the other connectors from the PSU (such as the power to the HDD's) inactive until the PC passes POST?
A: All connectors are powered once the PSU starts the PC, power needs to be distributed for POST to check hardware function
QUESTION 3 (with prelude): P:Another weird thing. That connector appears to have pin holes, but so does the corresponding port/connector on the MB. No pins anywhere to be found. Is it possible the pins all came off when I disconnected this connector from the MB? There are no traces of pins or evidence they ever existed - 0r that it somehow doesnt use pins at all?
A: Dell (and others) use the same motherboard for many models. Often the motherboards have different specs and features so unused features are not added to the board (the most common thing to find are empty PCI slots). They never had pins or headers, they simply got soldered over
QUESTION 4: Where might I find a diagram that tells me what the other pins are for on this connector an what do I test for? The manual does not supply this info. (If I could determine which pins on the MB side were for the switch, I could jump those).
A: Now you're getting into tricky territory, often the schematics are held tightly by the manufacturer, you can get them but, expect expense (possibly even subscription requirement), usually not worth the money to do so
QUESTION 5: There were other "solutions" I came across, but the just didn't seem likely. Clearing the CMOS by jumper or removing the batter, replacing the bettery itself, or cooking the video card (reflow). Also something about the ribbon cable.
A: Clearing CMOS will often bring a "dead" PC back to life. The CMOS battery in Dell machines plays a big part in operation (I haven't figured that one out) and often the machine will not boot (or may act strangely) if that battery is bad. Ribbon cables can go bad, they are much more frail than SATA cables but I think the other solutions should be tried first.

I'm going to address reflow separately since it is an often considered "solution". In a nutshell, don't. I think the longest I've heard of a reflow working afterwards was about 6 months. Unless you are absolutely positive that the graphics card is the issue the risk to it is far greater than any possible short term fix. (I own a reflow oven). If the graphics card is faulty and a reflow can work, take it to a profession shop and have them reball it (new solder applied) - depending, a replacement may be cheaper

Those were awesome questions, hope my responses helped

 

[lonwinters]

Oh yes, your answers helped immensely.

In a nutshell, you confirmed what I suspected all along, that there's just no easy to way narrow down these problems, even if I am lucky and the fix is relatively inexpensive.

For example, your description on testing a PSU makes sense. But I don't understand why these "sources" on the internet post what they do - such as the test that I did. They also claim you can get a PSU tester for $30. I suppose that's why the repair shops can do what they do - they know the proper ways to test, have the proper equipment and if needed, have plenty of spare parts around to just put in a see if they work.

I don't like blindly buying parts just in hopes that will fix the problem. It doesn't take much of this until you're not that far from a new machine.

So it looks like I'm back at square one. I'm going to put these two computers on ice for the time being. I've checked out this Pentium D a little closer, and it turns out that it's not that old - supports 64 bit, all my RAM and my SATA drives. That gives me a somewhat decent machine. Yeah, I have a couple quad CPU's left over, along with a nice video card, and TV tuner. Maybe if I keep my eyes open, I'll find a case with a working PSU and mobo that I can rebuild in that direction.

I really appreciate you're taking the time to answer my questions - all of them and so thoroughly.

One follow up question if I may -

Being as that these two machines are displaying the same symptoms, could it be that the load I put on the USB system may have had something to do with their demise? I always had lots of devices connected - yes, most of them either self powered of via a powered hub - but I get the feeling that it still puts a strain on the system. Possible? Or, cheap power strip with so-called surge protector in leui of a real batter backup unit.

 

[C12Friedman]

If you haven't done this already, I'll suggest picking up one or two CR2032 batteries (or at least checking the CMOS batteries are showing 3V), I can't begin to say how many times that's all that's been needed on "dead" Dell PC's I've been given to work on

The reason those PSU "tests" are posted is that they do show if the PSU is totally dead or it's voltage regulation is so far off as to render it useless so that is something. This is undoubtedly the best article concerning power supply testing I've found: Why 99 Percent of Power Supply Reviews Are Wrong . It's by Gabriel Torres of HardwareSecrets and IMO, is very much worth reading even though it is about testing PSU's for "Reviews", it does cover just what is needed to go about testing a PSU properly. The little PSU testers do serve as another type of very rudimentary testing that is available (easier to use for most than a multi-meter but basically doing the same thing) Mr. Torres also shows the flaws of that type of testing in the article. For me it brought a whole new light to the reasons justifying a quality PSU.

I have had laptops in the past that warned against using powered USB hubs because the laptop did not feature any kind of protections but I don't know that I've ever seen that statement in reference to a desktop system.

You might look over the motherboard for swollen or leaky capacitors or other indication of problems. Don't neglect to check the small caps like in this example http://postimg.org/image/wk2jmokfh/ (I had to add that as I've never seen that type of capacitor blown up before). That is from a PC that would run for a while and then restart, the owner was absolutely positive the PSU was the problem! If you look near "HDMI" you see what's left of a blown up capacitor and near "3.0" there are two severely melted capacitors plus a burnt MOSFET (7030AL), point here is the motherboard's VRM (Voltage Regulation Module) can cause issues often associated with a bad PSU so it's something to check. Often, problem components are not so obvious as in that picture and may simply involve slight burn marks or discoloration. Again, some things to look for

Most surge protectors use a MOV (Metal Oxide Varistor) to protect against overcurrent events (even small ones), basically providing the same protection as a UPS, the primary advantage of a UPS is the ability to save data rather than lose it during a power outage. Some UPS's do feature "line conditioning" which isn't present on most budget strips so there is that. Tom's has been doing some comparison slideshow articles about cheaper surge suppressors http://www.tomshardware.com/picturestory/675-cheap-power-strip-tear-down.html and http://www.tomshardware.com/picturestory/676-cheap-power-surge-protector.html

 

[westom]

3. Both passed the manual multimeter power supply test - fan came on and all voltages at all active pins on the 24 pin connector are correct.

Thousands of dollars in test equipment are required to design a power system. But a meter, if properly used, can report the state of all parts of a power system (PSU is only one part) - without doubt or speculation. Your measurements are useful only when numbers are provided and when each voltage was measured. Furthermore, numbers that most assume are good are actually reporting defects. IOW you have shorted your best assistance of facts. Without those numbers and how measurements were made, then nobody can say anything useful.

Best answer for the battery is also by using a three digit meter. Measure its voltage to know if a battery is bad, good, and what its state will become in future months. Again, saying a battery is good means no useful assistance. Numbers from that measurement are necessary.

Bogus is a power supply tester. Since the entire 'system' (not just a PSU) must be tested. And three digit numbers must be provided. All three digits provide relevant information. Why spend $30 for that tester when a $12 meter reports so much more? Voltage numbers include information not apparent to most.

Blindly buying parts to fix something (called shotgunning) is a most expensive repair method that sometimes only cures symptoms and does not even say why the failure occurred.

A power system is the foundation of a computer. A power supply that boots and runs a computer can still be defective. And make other parts of the system appear defective. Until numbers from the power supply are provided using specific and requested instructions, then other parts can act defective; confusion abounds.

What do other wires on power connectors do? That also is learned once requested instructions result in the necessary voltage numbers.

Light on the motherboard reports something critical. If that light is on, then disconnecting anything (even when the computer is off) can potentially cause hardware damage. Nothing must be installed or disconnected when that light is on. Light says nothing about hardware being good or bad.

USB does not adversely affect a power system. USB only creates a few watts of power demand. With numerous other standard design features that make USB ports robust. But again, even good USB devices can act defective when a defective supply boots and powers a computer.

 

[lonwinters]

I'm still having trouble getting past the fact that both these computers ended up the same, power button does nothing. The only difference was that the first computer did show signs of PSU failure, occasional spontaneous reboots. I'm not sure if traditional troubleshooting would provide any useful information - seeing if the standby voltage is present at the switch and if the switch can be jumped.

Normally, I would have just scrapped both machines for parts by now and bought a new computer. But maybe it's time to build a computer so I can make use of the components, the ones I got in the first place for what I wanted the machine for, video. I have the two quad processors, a real nice PCI Express video card, TV tuner and a video accellerator that speeds up rendering ten times.

So what should I do next as a last ditch effort to figure out what's wrong and how far should I go before throwing in the towel and start building a new machine? Basically, if I can get either computer to get up and running for under $100 I would do that. Otherwise, I would start building. Ideally, the new one would be i& based and support Win 8 64 bit

Thanks again everyone!

Edit: If it's unlikely that having too many USB devices connected caused an overload failure, what about a single faulty device? I've seen stranger things - once I worked on a machine where Outlook either crashed or didn't load. After progressive re-installs with no luck, it turned out to be a bad NIC card. No idea of the how or why, but no more problems after replacing the card!

 

[lonwinters]

I'm still having trouble getting past the fact that both these computers ended up the same, power button does nothing. The only difference was that the first computer did show signs of PSU failure, occasional spontaneous reboots. I'm not sure if traditional troubleshooting would provide any useful information - seeing if the standby voltage is present at the switch and if the switch can be jumped.

Normally, I would have just scrapped both machines for parts by now and bought a new computer. But maybe it's time to build a computer so I can make use of the components, the ones I got in the first place for what I wanted the machine for, video. I have the two quad processors, a real nice PCI Express video card, TV tuner and a video accellerator that speeds up rendering ten times.

So what should I do next as a last ditch effort to figure out what's wrong and how far should I go before throwing in the towel and start building a new machine? Basically, if I can get either computer to get up and running for under $100 I would do that. Otherwise, I would start building. Ideally, the new one would be i& based and support Win 8 64 bit

Thanks again everyone!

 

[C12Friedman]

A faulty USB device can cause havoc to a machine, mimicking problems not associated with the device itself (I have a lengthy horror story involving a USB mouse that failed - I won't go into that here).
Try swapping out USB devices, see if any changes

 

[westom]

Recommended was a meter used with some requested instructions. A minutes of labor and resulting numbers mean the fewer who know this stuff can say what is wrong; recommend a solution. By not posting necessary facts (numbers), then your help cannot provide assistance.