Powering up but no screen picture

Hello all you experts. :)

I would post this in reply to http://www.tomshardware.co.uk/forum/252166-12-dead-motherboard-beep-bios-screen, but since it's closed I make a new posting.

Allow me to quote:

westom said:

Go back. Let's establish what is good - step by step. In this case in about 30 seconds.

Measure (and report to three significant digits) voltage on the purple wire where that wire connect to motherboard (push probe inside the nylon connector).

Also measure voltage on the green and gray wires both before and when power switch is pressed. Report those numbers and behavior as switch is pressed.

I expect these numbers to remain constant at zero. However these numbers are also important. Measure voltages on any one of orange, red, and yellow wires as the switch is pressed.

Hello Westom!

May I also take advantage of your expertice and helpfullness. I have the same symptoms: Powering on results in fans and disks powering up, but no screen picture lights up, just stays in sleep mode. I have disconnected all external units except screen.

At one point the system booted with only screen connected, but when I tried again with keyboard, it didn't. And since then not at all.

I'm running on a Gigabyte GA-73PVM-S2H, don't actually remember which Intel processor.

I have measured the following according to your instructions:

purple: 4,96
green 4,25 before, 0,029 after
gray 0,01 before, 5,14 after
orange 3,37
red 5,14
yellow 12,02
battery: 3,16

I'm really uncertain about what to do. I could try another power supply first, maybe. And if it don't help, I guess I must buy a new motherboard, CPU and memory and reinstall the whole thing.

I'd be really thankful for any help on locating the error before buying components blindly.

Kind regards,

1 answer Last reply
More about powering screen picture
  1. Voltages look OK. The green line - does it go back to 4 volts once you release the power switch? If yes, it lloks as if the PSU is working. If not, that may be your problem.

    Complete system specifications?

    The following is an expansion of my troubleshooting tips in the breadboarding link in the "Cannot boot" thread.

    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.

    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.

    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 (this is also a good way to test the power switch and the associated wiring), 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.

    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.
Ask a new question

Read More

Gigabyte Motherboards