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No Signal Issue

Last response: in Graphics & Displays
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October 1, 2011 4:42:20 AM

I'm currently having issues with my parents' PC. The PC is an HP Pavilion p6654y Magnesium Grey and the monitor is an HP 2010i. My PC suddenly started to have an issue where it cannot detect a VGA or DVI connection and it simply displays "No Signal." I remember it working fine a day ago. I shut it down for the day. When I booted back up, there was no signal. After a while, the issue disappeared, but returned the same day. I tried both onboard and a discrete GPU. Nothing worked. I'm assuming it's something other than the GPUs or the monitor (tried it with another monitor; same issue). Anyone know how to resolve such an issue?

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a b C Monitor
October 1, 2011 5:09:31 AM

The problem could also be the motherboard or PSU.

The following is one of my "standard" troubleshooting replies. With a commercial PC, you shouldn't have any kind of case problem so there should not be any need to disassemble the PC. So instead of breadboarding the system, unplug everything from the motherboard except the PSU, front panel controls, and the system speaker. Then jump down to the "==> START HERE" point.

I have tested the following beep patterns on Gigabyte, eVGA, and ECS motherboards. Other BIOS' may be different, but they all use a single short beep for a successful POST.

Breadboard - that will help isolate any kind of case problem you might have.
http://www.tomshardware.com/forum/262730-31-breadboardi...

Breadboard with just motherboard, CPU & HSF, case speaker, and PSU.

Make sure you plug the CPU power cable in. The system will not boot without it.

I always breadboard a new build. It takes only a few minutes, and you know you are putting good parts in the case once you are finished.

==> START HERE

You can turn on the PC by momentarily shorting the two pins that the case power switch goes to. You should hear a series of long, single beeps indicating memory problems. Silence indicates a problem with (in most likely order) the PSU, motherboard, or CPU. Remember, at this time, you do not have a graphics card installed so the load on your PSU will be reduced.

If no beeps:
Running fans and drives and motherboard LED's do not necessarily indicate a good PSU. In the absence of a single short beep, they also do not indicate that the system is booting.

At this point, you can sort of check the PSU. Try to borrow a known good PSU of around 550 - 600 watts. That will power just about any system with a single GPU. If you cannot do that, use a DMM to measure the voltages. Measure between the colored wires and either chassis ground or the black wires. Yellow wires should be 12 volts. Red wires: +5 volts, orange wires: +3.3 volts, blue wire : -12 volts, violet wire (standby power supply): 5 volts always on. The green wire should also have 5 volts on it. It should go to 0 volts when you press the case power button, then back to 5 volts when you release the case power switch. Tolerances are +/- 5% except for the -12 volts which is +/- 10%.

The gray wire is really important. It should go from 0 to +5 volts when you turn the PSU on with the case switch. CPU needs this signal to boot.

You can turn on the PSU by completely disconnecting the PSU and using a paperclip or jumper wire to short the green wire to one of the neighboring black wires.
http://www.youtube.com/watch?v=5FWXgQSokF4&feature=yout...

A way that might be easier is to use the main power plug. Working from the back of the plug where the wires come out, use a bare paperclip to short between the green wire and one of the neighboring black wires. That will do the same thing with an installed PSU. It is also an easy way to bypass a questionable case power switch.

This checks the PSU under no load conditions, so it is not completely reliable. But if it can not pass this, it is dead. Then repeat the checks with the PSU plugged into the computer to put a load on the PSU.

If the system beeps:
If it looks like the PSU is good, install a memory stick. Boot. Beep pattern should change to one long and several short beeps indicating a missing graphics card.

Silence, long single beeps, or series of short beeps indicate a problem with the memory. If you get short beeps verify that the memory is in the appropriate motherboard slots.

Insert the video card and connect any necessary PCIe power connectors. Boot. At this point, the system should POST successfully (a single short beep). Notice that you do not need keyboard, mouse, monitor, or drives to successfully POST.
At this point, if the system doesn't work, it's either the video card or an inadequate PSU. Or rarely - the motherboard's PCIe interface.

Now start connecting the rest of the devices starting with the monitor, then keyboard and mouse, then the rest of the devices, testing after each step. It's possible that you can pass the POST with a defective video card. The POST routines can only check the video interface. It cannot check the internal parts of the video card.
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October 1, 2011 5:39:27 AM

I did the first step with the PSU, CPU and MoBo. I heard several beeps (a pattern of short and long beeps). That should be a good sign. I'm going to move on to the memory.
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October 1, 2011 5:43:22 AM

I shut down the PC and booted with one stick of RAM. Silence. I guess the RAM might be my problem. I was wondering, was I suppose to keep the PC on during the first test, put the RAM in, and then reboot?
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October 1, 2011 6:03:41 AM

I actually connected everything back (including the RAM). The PC booted up and a signal was detected. Thank you very much! I'll see if the issue occurs again soon after a get a few things straight.

EDIT: BSOD after booting it up. It wouldn't turn on after that. I guess the RAM really is dead :/ 
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