View Full Version : Sis 748 board low +5 volt rail.

04-05-05, 10:56 AM
I have a Giga-byte GA-7S748 motherboard that gives me a low +5 volt rail.
This is only used for gaming, this board has always reported higher than average temps as well.

current setup,

1 5600 ultra
1 dvd-rom liteon
1 gig memory
2600 Athlon XP
kworld tv card
2 harddrives
Santa cruz sound card.

Anway I was getting weird problems in some games, even if the frame rate was high, I would lower frame rates, still the same problem. So I switched graphics cards, still same weird problems.

My motherboard bios does not report +5 volt rail, and only tells me temps, and shows the 12v and 3.3v rails as fine. MBM5 shows the +5 volt rail as varied between 3.5 and 4.5, out of spec.

So I switched power supplys, back to an antec 380 xr true power, that came with desktop case. This power supply was with the same board, and was RMA'ed and was never used tell now. The old supply that I had thought was bad was an enermax what came out of a server case, it was 350 watt model eg 351p-ve has a claimed 32 amp, listing on the +5 volt rail.

Now with the new power supply in the case, shows about the same low +5 volt rail, its showing 3.5-4.8 which in my book is out of spec. This will be the third power supply this board has had, its on its second 380 xr true power.

The old case was well vented, with a 92mm side fan, and an 80 mm rear fan with a slient boost thermaltake heat sink. When I moved the board to the other case, I checked out the board very carefully, no raised or bursting caps, everything seems to be fine. every program seem to work fine, I run RC5-72 24/7 have no glitches, no sudden reboots, the only problem is when I play games.

Also before switching cases and power supplys, it was a clean install of Windows, only games and game patches, I run a reg cleaner all the time, and I do not see any spy ware installed. I think it might be heat relelated, this system has always had high temps, for instance at idle it shows about 64'C, and with RC5-72 running can get up to 70-78, this is with different heatsinks. I started off with a Zalman with a big fan blowing on the copper heatsink, showed about the same temps. I installed it a few times to make sure it was installed properly, still about the same temps, when I switched to the slient boost still the same temps. When I switched cases it was a little worse in the desktop case, right now its showing 74'C with RC5-72, at idle it will show about 64-68'C yes thats celsius. Just to make sure that MBM5 was accurate, I downloaded speedfan, and the easy tuner, both show about the same temps, as the bios.

Even if I have the side covers off the case my temps are all above 60'C, but everything seems to work fine. I even decided to revert back some graphics card drives to make sure its not a software issue. I have high frame rates in games that I play, but my +5 volt rail is low, either this board eats power supplys, this will be its third, or maybe my board is bad.

The weird problems I have in games is like this, for instance in utk4, I run with no AA, and no trilinear, watching the fps with stat fps in console shows 50-60 fps running at 800-600. Durning instant action on my local maching, it not smooth translation to different elements, kind of like low fps, but its above 50, kind of like something is not like it should be.

Should I RMA my board, and see if its the problem, or just buy a new board on Ebay. The only thing I can really point my finger at is the low +5 volt rail, but having two power supplys show the same thing, and not noticing anything in any other applications makes me confused.


04-13-05, 09:23 AM
I just wanted to give all an update, after switching motherboards my +5 volt readings are now posting a 4.99 in the bios. It looks like I need to RMA my motherboard, it killed a 512 mb stick of pc3200 ram. Right now I am running a MSI km4am-v motherboard which is a nice via km400a based micro atx board.

My 5600 Ultra is running good under Doom 3, did not see any of the slow downs that I had earlier, everything seems to be in good shape. After looking at the bottom of the board it looks like some of the traces have cooked themselves, some are a little off color, it was most likely caused by the heat. It makes me think, that maybe the first PSU took out the board, or vice versa all this caused by bad air flow through the case.

I don't think I will buy another Antec case, or PSU as they do not cool very well. I just wonder how many other people have the same problems I have due to poor case design.


04-13-05, 10:10 AM
glad its sorted - air flow is your friend - I have a Jeantech 450watt 120mm Fan PSU which was rather expensive but well worth the money - its both cool and quiet and the rails r supurb.