Ga-p35-ds3p

[diif]

This motherboard had two graphics cards fitted. One of the graphics cards had a couple of exploded caps over the weekend and the PC was dead Monday morning. Caps repaired on the graphics card which now works but the motherboard is dead.

I measure 5v at the power switch but there is no fan spinning, nothing.

Does anyone have a service manual or an idea where to start ?

Thanks.

[diif]

Re: Ga-p35-ds3p

[ATTACH]82278[/ATTACH]

[T30M31]

Re: Ga-p35-ds3p

You can start by measuring the voltages at the main power connector. It appears to be a standard 24 pin ATX power supply connection. This link is to a page that shows the pin diagram with labels for all of the connections of a 24 pin ATX power supply.

http://pcsupport.about.com/od/inside...in-12v-psu.htm

Edit: There may be fuses on the motherboard that were blown. I would expect them to be close to the power connector. I can't tell from the photo if there are any fuses there. Is there anyway you could provide a more detailed photo of the area around that connector?

[diif]

Re: Ga-p35-ds3p

I've tested the power supply and that is fine.

[T30M31]

Re: Ga-p35-ds3p

When you tested the power supply was it connected to this mother board?

I suspect that when the capacitors exploded it shorted the power supply and blew a fuse on the mother board. I can't tell from the photos where the fuses might be if there are any. Without a schematic or service manual all I know to do is try to trace the power circuit visually and with a multimeter.

[diif]

Re: Ga-p35-ds3p

Hi T30M31,

It was a definitely known working power supply i used from my bench as i had left my power supply tester at home. I can see fuses on the motherboard for the USB ports but i can't see anything that i expect to look like fuses elsewhere on the board.

I was hoping a schematic would help me as i'm fairly new to diagnosing at component level even though i've been fixing computers and laptops for over 10 years.

I shall attempt to trace the 12v circuit and see if i can find anything blown.

Thank you for taking the time to reply.

[T30M31]

Re: Ga-p35-ds3p

Were the capacitors that exploded on the 12 volt circuit or the 5 volt circuit?

If you haven't already done so, you might check the "Power Supply On" signal from the motherboard. I think it is on pin 16 of the ATX power connector. I don't recall the level that is needed to turn on the p/s but you should see a change when you press the power button.

Edit: It looks like pin 16 is tied to ground (pin 15) to enable the power supply.

[momaka]

Re: Ga-p35-ds3p

Let's isolate the issue here, first. But first, some obvious questions...
- Does the PSU fan try to turn on at all when you try to power on the PC?
- When you replaced the caps on the graphics card, did you place them in the right way? If you don't already know, electrolytic, tantalum, and polymer caps all have a set polarity. If you put them in backwards, that might have created a short in one of them and caused the PSU to not start.

If you are absolutely sure the PSU works, try hooking it to the motherboard, but take everything out of the motherboard except for the bare essentials - that is, CPU, CPU heatsink and fan, and RAM. Leave the graphics card out or try a completely different graphics card. If the computer powers on, the issue is with the graphics card. If not, you'll need a multimeter and check all of the major rails on the motherboard (with PSU disconnected) for short circuit. I can walk you through that, but first just try to narrow down the problem as stated above.

I suspect that when the capacitors exploded it shorted the power supply and blew a fuse on the mother board. I can't tell from the photos where the fuses might be if there are any.

Motherboards almost never have fuses on their main rails. You may see some on 5V and 5VSB rail near the USB and rear ports, but nothing as far as main power goes.

[Lance Thornton]

Re: Ga-p35-ds3p

Please take a closer look at your blue pci-express slot near the hold down latch. There is an area of discoloration just near the 2 red striped caps. I cannot tell from the picture if all of the contacts are there. That may be where the original video card was that blew up, just not sure. Good luck!

[diif]

Re: Ga-p35-ds3p

Thanks for the replies guys, sorry for the delay i have been laid up with a bad back.

The graphics card was a good repair (I tested in another motherboard).

I did a bare motherboard test with just the CPU and memory attached and there is no life, the PSU fan does not spin.

I shall have another look at the board when i go to work later.

[momaka]

Re: Ga-p35-ds3p

You likely have a short circuit on the motherboard then. It's usually repairable, but requires some hunting with a multimter. Do you have a multimeter and do you know (at least vaguely) how to use it?

[diif]

Re: Ga-p35-ds3p

Hi momaka, yes i have a multimeter and know how to use it

I have brought the motherboard home with me this weekend, any help will be greatly appreciated.

thanks.

[momaka]

Re: Ga-p35-ds3p

Great!

Disconnect the motherboard from the PSU and remove all RAM. Leave CPU in the board for now. You may also want to remove the CMOS battery.

Next, start probing at the ATX connector on the motherboard for short circuit. That is, you are looking if any of the power rails (5VSB, 3.3V, 5V, 12V, and -12V) have a short circuit to ground. You may also want to get a diagram of the 24-pin connector. Here is one on Wikipedia:
http://upload.wikimedia.org/wikipedi...PS_signals.svg

Next, do the same with the 8-pin CPU connector.

If you see any readings in the 100 Ohm range or less, note them down and no which pin. Keep in mind, however, that it may take a few milliseconds for the caps on the board to charge (especially on a line with many caps), so it is normal to see a "short circuit that dissapears" after a seconds or two.

Also note that you do not need to take measurements of ALL of the power pins. Just one 3.3V pin, one 5V pin, and one 12V pin on the ATX connector is enough (i.e. you don't need to probe all four 3.3V lines).

One last note: the 12V rail on the 8-pin CPU connector is physically separated from the 12V rail on the ATX connector, so do separate measurements for these 12V rails.

Let me know what measurements you come up with and definitely post the units on each (i.e. Ohms, KOhms, and so on).

[diif]

Re: Ga-p35-ds3p

Cheers momaka,

I probed every pin because when i tested one of each they were all high KOhms.

1) 1.3 KOhms 13) 0 Ohms
2) 1.7 kOhms 14) 1.1 KOhms
3)
4) 263 Ohms
5)
6) 0 Ohms
7)
8)
9) 1.1 KOhms 21) 8.4 KOhms
10) 0 Ohms 22) 0 Ohms
11) 1.3 KOhms 23) 6.9 KOhms
12) 1.3 KOhms

ATX 3) 7.4KOhms 4) goes upto 25KOhms then drops to 6 KOhms.

thanks.

[momaka]

Re: Ga-p35-ds3p

I probed every pin because when i tested one of each they were all high KOhms.

It's not necessary that the short is on one of the main power rails. Could be on a derived power rail. But the above test is a starting point. That said, you may have to redo the measurements because the second set of measurements you did (where you probed every pin) don't look right (as in, user error).

For example, For pins 1, 2, and 13, you have 1.3 KOhms, 1.7 KOhms, and 0 Ohms respectively - but that can't be. On all motherboards I have worked on over the years, I have never seen a motherboard that has pins on the same rail not connected together (P4/P8 12V CPU connector aside). I bet that if you measure resistance between pins 1 and 2, or 1 and 13 or 2 and 13, you will get 0 Ohms (if you don't, really DO double-check that you are measuring the right pins and the operation of your multimeter).

Same thing with pins 4, 21, 22, and 23 - should all read the same resistance to ground and zero ohms to each other.

So double-check your measurements and let me know what you get.

Another test you could do is try to power ON the motherboard with the 8-pin 12V CPU connector disconnected. If it does power ON, you probably have short circuit on the CPU VRM (likely a MOSFET or ceramic cap). If not, the short is somewhere else. For this test, you only need the RAM and CPU installed in the motherboard and, of course, the PSU connected.

[diif]

Re: Ga-p35-ds3p

Hi momaka, what you are saying made sense but my meter was saying different. However i have just realised that the diagram was of the power supply connector not the motherboard, i had everything upside down !!

5VSB 264 Ohms
3.3V 1.3 KOhms
5V 1.1 KOhms
12V 1.8 KOhms
-12V 7.5 MOhms

As for the other test, still no life, neither the cpu or mobo fan twitch or move.

Thank you for your continued patience and assistance.

[momaka]

Re: Ga-p35-ds3p

That 264 Ohm reading on the 5VSB seems suspicious. Usually it's in the KOhms range too.

Before we dig in deep, try this test:
connect PSU to motherboard and plug PSU in the wall. Next, set your multimeter to measure DC voltage and check the voltage on the 5VSB pin. It should be 5V. If it's not, then the 5VSB is more than likely shorted. If it IS 5V, check if any of the regulators on the board get hot. That is all those black 3 and 4 -terminal rectangular components (google image SOT223 and SOT252). I see there are quite a few around the Southbridge. There is also one above the ATX connector, two under the blue PCI-E connector, and a few more where the Realtek and ITE chips are. Just touch them with your finger and see if they are getting hot (or even note if they are getting warm).
U104 (8-pin SOIC - google image SOIC-8 to see what I mean) is also of interest, so check if it gets warm too.

That's all for now. If we don't get any conclusive results from this, then the next step would be to check whick of these is connected to the 5VSB line. But all I wait to see what results you get.

[diif]

Re: Ga-p35-ds3p

Thanks momaka,

I get no 5V, so i guess there is a short somewhere, shall i stick some voltage into the 5VSB line and watch for smoke/ a warming up regulator or is there a more reasoned and rational way to locate the issue ?

[Agent24]

Re: Ga-p35-ds3p

That is one method of doing it... if you do, make sure you use current limiting, you want to heat a shorted part, not blow it sky high - which runs the risk of blowing out traces on the board as well. Hard to repair on outer layers, impossible on inner layers!

[momaka]

Re: Ga-p35-ds3p

I get no 5V, so i guess there is a short somewhere, shall i stick some voltage into the 5VSB line and watch for smoke/ a warming up regulator

Yes, you can do that, but as Agent24 mentioned, it is best to limit the current in some way. If you get several car light bulbs or MR16 / GU5.3 12V light bulbs and hook them all in parallel then hook that entire circuit in series with the 5VSB line, you can then feed the board with 5V (either directly from the PSU's 5V line by turning it on manually or from some other variable PSU that can give you several amps at 5V). This will provide the current limiting. A 20W MR16 / GU5.3 bulb will draw about 1A of current at 5V, so with 2 to 3 in parallel, you will have maybe about 2-3A. If it's a "dead" short circuit, you may need to add more. If it's not, the bad component/regulator will heat up.

The other way is to use your multimeter and see which of these regulators is connected to the 5VSB line. That is, take the red (+) probe of your multimeter and stick it in the ATX connector's 5VSB pin. Then use the other probe to check which regulators give you zero Ohms reading on at least one of their pins. The ones that do give you zero Ohms are the ones connected to 5VSB line.

Once you find which regulators are connected to the 5VSB line, plug in the PSU and see if any of them get hot.

Also, the next question for you is, do you have the proper tools/equipment to remove regulators from motherboards? If you don't have hot air, then you will need two high-power irons. Preferably 45W or more. Heat gun might be a bit "too much" for the board and you may damage other components (particularly capacitors).