Dimension 8400 intermittent failure

CharlieSummers

Try checking to see if the processor and chipset heatsinks are still firmly attached to the motherboard.

While the case is open, check the motherboard for any capacitors with bulging tops or are leaking, the tops should be perfectly flat.

Bev.

Apologies for the delay...a wetware virus took me out of action for a few days.

Your point to the heatsink was right on-the-money; I pulled back the airflow director, fired up the machine, and oh-so-gently put a touch of pressure (just one light finger) on the huge processor heatsink. I was rewarded with an immediate lock-up.

My plan now is to pick up another tube of thermal paste (I have a bunch around here somewhere, but the darned things always go missing), remove and re-place the processor sink (should probably remove the processor from the socket and re-place it as well), and see if the reassembled tower is more stable. Regardless, I still want to examine the motherboard's capacitors as suggested just to be through, but I'm pretty confident there's an issue with the processor connection.

Hum... After following the removal instructions at http://support.dell.com/support/edocs/systems/dim8400/SM/parts.htm#wp1057607 I used a touch of alcohol to remove the old thermal paste, a can-o-air to blow out the pins, two small dabs of fresh thermal paste, reassemble in reverse, and...

Nothing. Now I can't even get it to start by tapping the chassis. The only thing I get when I plug in the power cable is the fans reving to high within five-seconds or so.

I'm confident the processor was reinstalled correctly (pin 1 mark is where it belongs, but the board is keyed so I couldn't have put it in wrong if I tried). I've run it through my head multiple times, and I can't think of anything I might have done wrong (this is pretty straightforward, after all); I admit I didn't use a grounding strap, but I did the ol' plug-and-ground before I started, so it and I should have been at the same potential.

Any suggestions, or thoughts on anything I might have messed up?

CharlieSummers

That's a bummer. 

Let's start with the troubleshooting basics.

Is the power button LED, solid green, blinking green, solid amber, blinking amber?

Check the sequence of the diagnostic lights on the back panel of the case, see HERE.

Check all the power and data cables, memory modules, video and PCI cards are properly connected, by removing them and reinstalling.

Bev.

First off, I really appreciate the help.

Is the power button LED, solid green, blinking green, solid amber, blinking amber?

Solid (dull) amber.

Check the sequence of the diagnostic lights on the back panel of the case, see HERE.

I got...nuthin' - that is, the lights never light, suggesting to me it doesn't get far enough.

Check all the power and data cables, memory modules, video and PCI cards are properly connected, by removing them and reinstalling

Yeah, should have done that already, but was probably a little gunshy. Grounded, removed everything I could think of (SATA cables, no less), reseated everything, same symptom.

However, in plugging the power in-and-out, at one point I had my hand in the wrong place and got a diagnostic beep instead of that fan windup. When I realized part of the heel of my hand was against the processor heat sink, I decided to try something sorta ugly...I put considerable pressure on the top of the heat sink...more, frankly, than I would normally be comfortable applying to, inevitably, the motherboard.

The frelling computer booted to the Windows boot screen.

Clearly, something in the stack is seriously wrong, and my removing and reseating the sink and processor simply served to exacerbate it. Either the processor is not making contacts with the pins, or the heat sink is not making contact with the processor (which might explain the processor fan going bonzo).  But I honestly don't understand how that's possible...the processor is held down firmly by the clamp, the heat sink is held down by the bracket clips (not the green ones, I mean the black clips - those green side clips don't seem to do a whole lot, really).

Short of getting out a welding torch, how can I do anything about this? Heck, I'm ready to take a fine toothbrush to the motherboard pins if I thought it would help!

Ok, more experimentation. I tried cutting a few pieces of vellum (that plastic paper-like stuff the Mrs. and daughter use for craft things) to go along the sides of the bottom of the heat sink, to add just a snitch of pressure to the black plastic tabs that hold it in place. No joy, processor fan still pretends to be a jet engine.

Then I reached into it with my hand (the vellum pieces still in place, although I doubt it has anything to do with it) and squeezed manually on the tabs, squeezing in toward the center of the sink. In a Rose Mary Woods-like maneuver (that reference really dates me), I plug the power cord in and am rewarded with a gentle beep. I then reach around (still squeezing the tabs) to the power switch on the front, and hit it...the machine boots to the Windows boot screen. (It's been abused so in the past few days it's going straight to the boot selection screen.) While it's counting down toward normal Windows boot, I gently remove the pressure, and before it is completely released the countdown stops, indicating a lock-up.

It is pretty clear the problem is in the amount of pressure exerted downward on the base of the heat sink. But I honestly don't know what I can do about that. I've never seen anything like this before...has this kind of problem ever been reported before? Is there any reasonable solution?

CharlieSummers

What you are saying, is the heatsink does not stay firmly attached to the motherboard.

Are the two green plastic retention module clips loose? 

Maybe replace the six pipe heatsink and clips would help.

This has been an ongoing problem with the 8400 systems, plus some of the early 8400's were also shipped with defective six-pipe heatsinks. [Google 'Dimension 8400 noise']

I have an 8400, that had the same problem, but instead of using a replacement Dell heatsink, I carried out the following:

Installed a Zalman 'CNPS7700-Cu' 918gram [2+lbs] copper heatsink, with a 120mm fan, while the installation was not quite as easy, as described HERE, it is still doable and is still working well.

Bev.

What you are saying, is the heatsink does not stay firmly attached to the motherboard.

Yes...there doesn't seem to be enough downward pressure on the heat sink to keep it solid to the processor.

Are the two green plastic retention module clips loose?

For the experiment I mentioned, they were off completely. But I frankly don't see what possible good they would be anyway in this particular situation; they are such lightweight little things they don't exert any downward force when in place (I have then reinstalled now, and can easily wiggle them around, showing there's no pressure on the heat sink mount). Truthfully, I'm not sure I see the purpose of them at all, while I do dutifully replace them as instructed by the instructions. But they don't seem to be "retaining" much of anything. (The ones on this unit do not look like the much heavier ones depicted at http://support.dell.com/support/edocs/systems/dim8400/SM/parts.htm#wp1057607 - those look like they might accomplish something. The ones here are lightweight plastic broken at the top for stressing into the mount slits.)

Maybe replace the six pipe heatsink and clips would help.

Actually, I'm wondering if the problem isn't the heatsink mount; if that black-plastic squarish mount fastened to the motherboard by four bolts has stressed out-of-square (outward in the direction of the power supply and the reverse), it would explain the two mount tabs not exerting the proper downward pressure onto the lips of the sink, and why when I manually squeeze them together it does. I'm really wishing right now this thing were steel instead of plastic...and I'm betting there's no way to order a replacement from Dell to even verify this is indeed the problem. (Edit: a little searching found a pull at a discount outfit for $5.)

Installed a Zalman 'CNPS7700-Cu' 918gram [2+lbs] copper heatsink, with a 120mm fan, while the installation was not quite as easy, as described HERE, it is still doable and is still working well.

Wow. Extreme, but it does deal with the possibility that the heat sink mount is the problem, since it's replaced completely.  I wonder if there is a less...awesome...replacement sink I could install. This is a "family" computer, one used for the owner's kids to write schoolwork and such on, so fan noise is somewhat  less of an issue. A two-pound, five-inch-wide, $50 sink seems a little...er...overkill for a non-gaming machine.

And again, I appreciate your help and advice. I've been mucking around with computers since 8-bit processors and CP/M, and have never seen anything quite like this before.

CharlieSummers

A replacement heatsink bracket and clips for the 8400 can be purchased from HERE

Bev.

A replacement heatsink bracket and clips for the 8400 can be purchased from HERE

Yep, that's where I found it...was reluctant to post the pointer, since some boards frown on third-party sales links.

I'm going to give a replacement bracket a try first, and if that fails, take a deep breath and follow the lecodesign.co.uk instructions for the Zalman heat sink. My gut tells me that even if the bracket fixes it for now, it will eventually fail again, but maybe by then the family will buy a netbook. ;)

(Before I forget, my eleven-year-old daughter loves your avitar. She's a cat fancier, too.)

CharlieSummers

Good luck with replacement heatsink retention bracket, hope it will take care of the problem, when it's complete, please give us a feedback.

It's not a violation of the T of S, to post a third party sales link, but you cannot use the forum for advertising merchandise to sell.

The Forum rules are HERE.

Tell your daughter, my cat's name is Bubbles, because she has a bubbly personality.  LOL

Bev.