Motherboard Power issue - Gigabyte EX58-UD5

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Motherboard Power issue - Gigabyte EX58-UD5

Postby jinu_j » Mon Jun 27, 2016 5:54 pm

Hi Folks
I have weird problem with my motherboard. It randomly does not power on. Earlier this used to happen very rarely, but now it is the default behavior. Out of the 100 times i press the power button it comes on just once. So let me tell you how the motherboard behaves:

1. On switching on the power supply on/off switch at the back of the power supply, the power switch on the motherboard lights up (i believe this is based on the 5 volts its gets from the green signal wire). The Gigabyte Ex-58-Ud5 has a backlighted physical poweron switch on the motherboard.
2. But pressing this switch on the motherboard has no effect. The motherboard does not power on.

So these are the following things i tried:

1. I replaced the power supply with a known working power supply. Same issue
2. I shorted the green wire of the power supply with the black with everything plugged in. This causes the other peripherals on the motherboard like fans, the error code LED display to power up and work, but the mother board main components do not power on. The minute i remove the short, the power goes away completely. If i do this some 10 or 20 times, the motherboard powers up and works fine.

Once the mother board powers up there is no issue in performance and from windows if i restart, the PC restarts fine. The problem comes if i shutdown and wait for 10-15 minutes or i switch off the power supply, then i am back to square one, with no power. Now in the working condition, pressing the Case power button or motherboard power on switch has the same effect of powering on the motherboard.

My guess is this points to a failure of a capacitor or inductor on the board. This motherboard has only Aluminium Polymer Capacitors which are supposed to be very resilient and not prone to failure. Since it works fine once the Motherboard powers on, i dont think there is any major component failure.

Any ideas on how to proceed and repair this
jinu_j
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Re: Motherboard Power issue - Gigabyte EX58-UD5

Postby Karlsweldt » Tue Jun 28, 2016 8:48 am

One of the first paths to try is a new BIOS battery. Typical life is about 3 to 4 years, depending on use.
While only a redundant backup for the BIOS and CMOS needs, it also powers the real-time clock when no AC mains power enters the PSU. If the real-time clock is not working, timing circuits may not energize.
The +5 volt stand-by source powers the BIOS and CMOS circuits even when the PSU not active, as long as AC power is 'on' for it.
I would look over all the capacitors for domed tops, excess lean or signs of leakage. Even the best capacitors can fail due to excess heat.
Any system fans that connect to motherboard headers may be monitored by the BIOS. Ensure each is on its respective header, and if a fan has no RPM monitor, set the BIOS control to 'ignore'.
There is a gray wire at the back of the main ATX power plug. This is the PG or 'power good' signal from the PSU to the system timers. Should be at +5 volts, if all is good, after the PSU load stabilizes. If at +4.8 volts or lower, the system may not show any life signs. Measure only with a digital meter, so as to not load the signal voltage.
Also reseat all device cards, power leads and memory.
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Re: Motherboard Power issue - Gigabyte EX58-UD5

Postby jinu_j » Thu Jun 30, 2016 6:31 pm

Thanks for the response.

I replaced the battery as the motherboard is 7 years old. But that did not resolve the issue
The capacitors are all Aluminium Polymer capacitors so there is no visible damage to any of them
I have disconnected all devices except for CPU fan and graphics card but still no hope.

Any ideas on how to proceed. Any places on the board that i can check for voltage or path.

Now the board does not power up at all, the earlier random starts have also stopped.
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Re: Motherboard Power issue - Gigabyte EX58-UD5

Postby Karlsweldt » Fri Jul 01, 2016 5:17 am

At this point, a 'bare bones' setup for testing would be good. Remove the motherboard from the case to check if there is any stray hardware somewhere. It happens! Look over the bottom of the motherboard for any possible smoke or discolored spots. Hope none are found. Take the CPU off its mount, clean off and reapply the compound but very sparingly. Ensure the heat sink is properly secured. Alcohol or Naptha is the best to remove old heat sink paste.
Reassemble, but with minimal memory content, just the CPU and video. No extra device cards or drives. If still no go, then a proper tool to have would be a POST diagnostics card. It displays a two-character code for each of the POST steps, and if any code hangs, that is a clue as to where to start sleuthing. Some start at around $20.00 USD, can range to more than $200.00 USD for 'pro' models.
The only area where voltages can be checked is at the main ATX power plug. Any black wire is common to all voltages.
The reading should be within +/- 2% of true, 1% is ideal. The -12 volt source could be off by 10% and still be good.
There are several voltage regulators near the CPU, but contact leads are very close. Too risky to bridge the wrong ones, and destroy the CPU or motherboard.
Check each memory module separately in the first-detected slot. One may be bad.

As previously noted, that "PG" signal wire should be at +5 volts after the PSU load stabilizes. If low, the timing circuits will not become active. Not recommended except for testing purposes, a 47 ohm 1/2 watt resistor could bridge from a +5 volt power lead to that "PG" lead to see if the system becomes active. But do so for no more than a minute, or permanent damage may be done.

In replacing the BIOS battery, the CMOS has to be reset to default or there may be conflicts. Pull the power cord from the PSU, try a few starts to drain reserves. Remove the battery, move the "clear CMOS " jumper to 'clear' for about 15 seconds, then reverse the order and try a power up.
There is an 8-pin socket near the CPU. That must be connected to a lead set from the PSU for power needs. Check the board's manual to see if only a 4-pin plug can be used, or an 8-pin plug is mandated.
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Re: Motherboard Power issue - Gigabyte EX58-UD5

Postby evasive » Sat Jul 02, 2016 11:12 pm

Your known good power supply may have fallen to the same issue as the earlier power supply, bad capacitors. Known good power supplies are from a reputable brand and have a decent waatage, enough to power up your system. Please list brand/model of the power supplies you tried so far and give a general list of parts that your are trying to make run with this board, then we can do an educated guess on if it will work or not.
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