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PC does not start


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#1 Dick73

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Posted 10 March 2014 - 01:50 PM

I have a PC  1 1/2 years old based on PH77V, motherboard, i5 2500k Intel CPU, 2 x 4 GB DDR3 1600MHz, 650w power supply, 2 SATA hdds and a DVD disk reader/writer

A couple of days ago the PC turned off and on by itself two or three times and then remained dead, I assumed it could be a short someplace.

I tested power supply without load and voltages are within range and I installed the power supply in an older PC and it worked fine

Following ASUS support, I took everything out of the case and reassembly the system, except de dvd and hdds on a “white board” to see if it starts POST

Then I installed the power supply into the PH77V and connected to line voltage the system.

The power and chassis fans run a second and stop and enter in a loop of run a second and stop some 3 seconds and so on, nothing else happens, no beeps.

I changed motherboard battery without any result. There is no sign of damage in MB capacitors

I connected the PH77V to an older 400W ATX power supply that had a 4 pin EATX 12V instead of the 8 pin EATX 12V that the mother board requires (because that possibility is considered by ASSUS support) but the same loop on/off appeared

I don’t know if it is the mother board or the CPU that fails.

Can you give me some ideas on how to follow checking?



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#2 zingo156

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Posted 10 March 2014 - 02:05 PM

Disconnect the power button and reset button from the main board, try and short the 2 power button pins with something metal (this will not damage anything as the power button actually does exactly this: it shorts those 2 pins to power the machine on) maybe you have a bad switch...

 

If you still get the loop, try pulling out all sticks of ram, put only 1 stick back into 1 slot. If you still get the loop move that stick to the next slot and re-test. If that stick fails in all slots, try your other stick in all slots.

 

If you still can not get it to work, remove every component that is not necessary for the computer to fully post. Leave in the cpu/cpu cooler, 1 stick of ram, video card (if you have onboard leave the addin card out), and the power supply. DISCONNECT all usb/audio headers from the main board (if you have front case usb/audio disconnect it). Disconnect all hard drives, disc drives, pic cards, pci-e cards etc. Visually inspect all main board usb ports for any damage or shorting pins.


Edited by zingo156, 10 March 2014 - 02:08 PM.

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#3 Dick73

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Posted 12 March 2014 - 08:43 AM

Problem solved

I appreciate your help. Following your advise I discovered al almost microscopic metallic particle shorting two pins of NTC 7677 integrated circuit and carefully removed it.



#4 zingo156

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Posted 12 March 2014 - 09:11 AM

Glad I could help, good eye spotting that.

 

I once had a laptop where there was a lose screw hiding in the bottom plastic chassis, I took it apart 2 times and bench tested the components outside of the case. Both times outside of the case everything worked fine, after putting the components back in, it powered on for a second and then powered off. It took me 2 tear downs to figure out there was a screw sitting in a corner causing a short... I also had a desktop where there was a very small bit of metal shorting some pins in a ram slot. I used an air compressor to clean it out problem solved. No idea where it came from but luckily the main board with speaker was throwing memory fault so I was able to somewhat quickly figure out there was a ram problem, bad board, or short. Shorts are usually not fun to deal with. Most of the time I see USB port shorts from people ramming things in the port incorrectly.


Edited by zingo156, 12 March 2014 - 10:17 AM.

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