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Rail fluctuations

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  • Power Supplies
  • Hard Drives
  • Components
Last response: in Components
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July 8, 2004 12:27:39 PM

I've got a P4 on an MSI motherboard (MS6585), CD-RW, DVD, 1 HDD, GeForce4 MX440, firewire card, tv tuner, an audigy2 soundcard, a hdd cooler(used as an intake fan!), a pci exhaust blower, and a 92mm fan. Suntek case with a 350W power supply.

Heres the power supply ratings.

12V-16A
-12V-0.8A
-5V-0.5A
+5VSB-2A
5V-30A
3.3V-22A

I use corecenter to monitor temps and voltages. Recently i noticed that my 3.3v rail is quite low around 3.15. I had an incident where the rail dropped to below 2.7, the corecenter alarms went off and eventually the system froze. I had no idea what caused this, so i opened the case up had a quick look around, nudged and poked things, all seemed ok. I restarted the machine and it was fine. Although not ideal the 3.3v was at 3.23 (fluctuating by 0.01V). Now after putting in my audigy2 card i see the 3.3v is stable at 3.14 (same fluctuations).

I do from time to time get much larger fluctuations. But the 3.3 doesnt go below 3v.

The other rails are very steady.

As far as i know pci cards run off the 12v rail so why would this happen? Also, after adding the card the 12v rail which used to show 11.76 now shows 11.96!?

If anyone could explain the incident where the rail just dropped dramatically i'd appreciate it.

Are rail problems always due to the PSU or could the motherboard be to blame?

More about : rail fluctuations

July 8, 2004 6:59:29 PM

Your negative voltages are irrelevant for your setup, as I'm sure you know. You failed to mention what kind of PSU your running in your rig. If you have a generic or P.O.S. (Piece Of S...) one, then you know what to do.

If you have a quality PSU, what kind is it and how long have you been using it for? Also, and this may be a long shot, check your cabling. 1st thing that everyone knows to do but usually forgets to check. As some last restors, if your using a UPS or surge protector, try another surge protector. It could also be the wall socket, your PSU socket, or a transformer problem.

A good PSU should not fluctuate if your AC voltage is low or high (read: not in the middle). The voltage should be steady. But if your AC voltage is REALLY low, then no amount of voltage regulation on the DC end is gonna help if your system requires lots of power. But it is normal for your DC voltage to decrease SLIGHTLY as you tax your PSU with more and more parts, requiring more and more power. The important thing, whether there is a slight decrease or not, is making sure the voltage rail lines do not fluctuate. Yours increased (which is Okay) but too much of an increase is not great.

Lastly, it is possible that your mobo is not functioning properly. It may be drawing too much current, eating too much power.

If I were you (after all of the above), what I would do is run the bare essentials and monitor the voltages. If all is good, add another part. Oh, check for any grounding problems in your case (e.g. loose screws). Grounding is a fundamental concern in this issue of ours. Make sure that you don't have that problem!
July 9, 2004 5:16:54 PM

How do i test for grounding issues? I did have some major problems when building my computer (it was my first attempt). The case came with small metal hook type things which hooked into the motherboard holes and I've only got one screw holding the motherboard to the case. How can I tell if grounding is an issue? The concept of grounding is kind of unclear to me.

I also took the audigy2 card out and the 3.3v rail went back up to 3.23.
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July 9, 2004 7:14:35 PM

OK, there are two things I need to tell you.

1) One screw holding the motherboard down is asking for trouble. Allow me to explain. On the back end of your mobo, closer to your pci slots, there is a screw hole that looks wider than the rest. This particular screw hole is very important to lock down, with respect to grounding. In fact, it is recommended that you provide a screw for every hole - better safe than sorry. Voltage is electric potential and thus is always referenced from point A to point B. If your point B is not grounded, voltage will leak (in most cases). In order to minimize voltage leak, you need a commond ground and filling up all those screw holes completes that task. This is probably what is causing you problems. Make sure you fill in all the screw holes and DO NOT tighten or use an automatic screwdriver.

2) If you discover that your still having problems, take out your mobo and place it on wood or cardboard. [If you use an anti-static bag, make sure it's big enough to cover the bottom of the board and that it hasn't been abused, although there are harsh critics who swear that used anti-static bags can damage your parts. For the record, I have never damaged any components. Just use your common sense - don't stick the bags in mud or drag it across carpet for hours on end.] Start up the essentials - psu, cpu, video card, ram, mobo, storage device - and monitor the system. If all is go, add more parts and repeat.
July 9, 2004 10:54:11 PM

Here's my case, http://www.suntekgroup.com/stk6551.htm

I'm using the power supply that came with it. If you checkout the features you'll see stuff about snap-on standoffs. Now the standoffs (which i was reffering to as 'hook things' in my previous post) don't allow me to easily insert the screws. In the centre there is a brass standoff for some reason which is nice and easy to attach a screw to. That is the only place I had attached a screw. The other standoffs don't have any screws as the bit that hooks round stops the screw going in very deep, and also it seems that the hook is more than sufficient to hold the board in place.

i did have sever grounding issues when i first built my pc (about 8 months ago). That's when i tried to force all the screws into the standoffs. I then removed the screws from the snap-on metal standoffs and only had the one in the brass standoff and all worked fine.

I seem to be waffling a bit here. What I'm trying to say is if grounding is an issue here shouldn't my pc just not boot at all like before?

You say having only one screw is asking for trouble, but when I had all six in it wouldn't even boot!

I also did some reading on the web and the holes in the motherboard have insulating rings around them, so how can the screws play apart in grounding if theres insulating material between them and the board?

Also i couldn't find that wider hole you were talking about. I just have 6 similar holes.

Check this picture, http://www.msi.com.tw/program/products/mainboard/mbd/pr...

(Click on the picture for a better view)

I appreciate your help. This pc I built never went smoothly. There was always problems with it (mostly due to my lack of experience). Even now it isn't 100% (the rail problems). But I got some time on my hands and wanna sort all these little problems out. I never thought that screwing the damn thing in would be the hardest part!
July 10, 2004 6:54:43 AM

It is late and I will explain as much as I can, for as long as I can. Some of the comments you made I will perhaps respond to for another time.

First of all, I don't have the time to research who manufactures Suntek PSUs. And according to the link, your psu is 330W rated, but I have no idea about anything else about it. Is that it's peak wattage or continous wattage? Is it rated at 40 centigrade or 30 centigrade? Does it have active, passive, or no PFC? These are questions that you should ask the manufacture or look at the manual or look at the psu itself. There should be some indication for those things. And I doubt it draws 330W. It probably draws between 250-300W, but that's just a blind shot in the ball park. See if crashman is around. He may have the time to figure this out. I don't, sorry. In fact, I just did a very brief check on the specs of a 300W PSU and they rated it at 25 degrees it seems. I don't know, but if I want a quality PSU, I don't want the manufacture telling me the wattage at 25 centigrade when an average consumer PSU operates at rougly 40 centigrade (or 50 centigrade for industrial PC's).

Grounding is not an on or off thing. For example, your PC can turn on and then restart itself or shut down completely. If you physically shake it around, you can upset it that way, too. Grounding is a nuisance and can seem random in its execution.

About the screw holes, my apologies. I failed to mention I was using my board as a reference. OK, all 6 holes should be screwed in and if you overtighten them, then your pc won't boot! You don't want the screw to touch the bottom of the case - that's how you kill or damage your board. That is an example of what improper grounding can cause. But with your case, you should ask your manufacture what is the correct installation procedure for a mobo. Oh, the insulation in itself is useless if you don't make use of it. That is why you use screws. It insulates the mobo from EMI (electromagnetic interference).

So, my recommendations at this point: Call your manufacture and ask them how to install the board (I just am scrapped for time to investigate this part of your issue). If someone else will volunteer their knowledge and knows more about this particular thing I do, then perhaps they will step up and speak. Also, find out who makes that PSU (Suntek probably won't tell you or tell you the truth). For example, Zalman PSUs use some Fortron parts like the heatsinks in their PSUs. And Fortron PSUs are quality (and Zalman, of course). If my hunch is right, that this PSU from Suntek sux, then you must get something good and at least 400W. You can get a real nice 400W PSU from Fortron or Zalman, both of which make quiet PSUs, especially the latter. You can never have enough power! Once you have all those issues sorted out, try again and see what happens. With problems, you start small (check for grounding) and work your way to the top (bad transformer).
July 10, 2004 1:51:50 PM

Thanks for your help.

However, I'm worried about tinkering with the motherboard. Its working fairly stabily now and i don't want to accidentally upset it. I don't get any random reboots or hangs.

The rail problem I was talking about, I may have made it sound more serious than it is.

My rails show as follows on CoreCenter,

vCore - 1.47 (1.46 - 1.49)
3.3v - 3.23 (3.22 - 3.25)
5v - 5.08 (5.11)
12v - 11.96(11.90)

The rails fluctuate to numbers shown in the brackets. Is this normal? Is the rail supposed to be very steady (no fluctuation at all)? Could this be a fault in CoreCenter?

I appreciate the time and effort you are putting into my queries.
July 10, 2004 4:49:43 PM

I made a mistakea bout one thing. When I said that the screws shouldn't touch the bottom of the case, I meant the mobo shouldn't touch. The screws should touch the bottom of the case. In this way, you elminiate grounding or it becomes negligible. Your voltages look OK. But you did mention that the 3.3 rail dropped to 2.7. I told you what I would do if I were you. If everything is OK now, you haven't seen anything where your computer froze because of voltage fluctuations, then make sure you keep an eye on this. Everything comes from from the 12V rail, unless the PSU is designed with sepearate voltage lines.
July 12, 2004 5:37:24 AM

Core Center is faily accurate on voltages. I just dumped a power supply that dipped to 3.18v on the 3.3v rail when I added a stick of memory. You are on the low side too with only 16a on the 12v rail with an MSI NEO 865PE board.
Keep an eye on it.

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