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Monitor has no signal from PC


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#1 zeta2reticuli

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Posted 11 November 2012 - 06:01 PM

Hi there,

I have a Dell XPS720 running Windows XP and an nVidia GeForce 8800 video card. Some time ago, on booting up the computer, the display reverted to the lowest resolution and I received a message that the video card driver was not working. However, this seemed to be a spasmodic problem as I managed to get the driver working again sometimes. Occasionally however, booting up the computer resulted in a scrambled 'frozen' image that required a restart. Now however, the monitor does not even appear to communicate with the computer, and does not register any signal when the computer is turned on. The monitor is powered appropriately and seems to function as normal - just not registering the Pc. I have tried again by connecting a different monitor and had the same issue - no signal from the computer and the monitor just goes into Power Save mode.

can anyone advise me what the problem is likely to be?

Many thanks for your help!

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#2 caperdog

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Posted 11 November 2012 - 10:14 PM

if you do not see the POST (power on self test)screen or POST info at start up then it is not a windows or driver issue, it is hardware.
possibilities: the monitor , you seem to have ruled that out
the video cable , did you use the same one when you tested the other monitor ?

the video card , you could try to remove it and reseat it. is the fan working ? if not the card may have overheated.

#3 Nanobyte

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Posted 12 November 2012 - 12:23 AM

if you do not see the POST (power on self test)screen or POST info at start up then it is not a windows or driver issue, it is hardware.....

The above is not necessarily true. I have an old ATi video card and if I connect to a monitor via DVI, I see nothing until the Windows screen appears. My old CRT and VGA output would show the POST briefly. I suppose one could say that is a hardware issue but not a problem. I've never looked into why. If I had zeta2reticuli's issue, I would revert to VGA just to see what happens (if that is a possibility).

#4 zeta2reticuli

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Posted 12 November 2012 - 03:08 AM

Thanks for your replies. I get no POST screen at all on startup. Instead, the monitor behaves as it does when the PC is off (i.e. it shows text and then goes to power save mode). The computer fan is working and I hear no beep codes. Am pretty sure that I tested a different video cable but will try again and let you know the outcome...

#5 zeta2reticuli

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Posted 19 January 2013 - 10:52 AM

Just getting back on top of this problem. Have confirmed that the monitor works fine, the VGI cable and DVI adapter work fine (on another machine), so I think that the problem is nnecessarily narrowed down to the video card. Over the weekend I will try to open up the computer and reseat the video card, and will let you know what happens.

#6 rotor123

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Posted 19 January 2013 - 01:57 PM

It could be the Video card or it could be a Motherboard or Memory or Power supply problem. For example if one of the voltages the power supply puts out is bad then no post. Same with bad memory or a bad motherboard.

I'm just trying to say do not rush out to buy a Video card and expect that it will fix the issue. Just as an example, last year I worked on a Dell with no video. That turned out to be a bad modem. When I pulled out the bad modem it worked. However it also has a capacitor going bad so I changed that as preventative measure to head off future problems. I had a used modem of the same make and model laying around so I popped that in in case they used it to fax anything.

A computer is a complex thing where many things interact.

Do you get a error code set of beeps with no video card?

Good Luck
Roger

Edited by rotor123, 19 January 2013 - 01:57 PM.

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#7 zeta2reticuli

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Posted 19 January 2013 - 06:09 PM

Hi Roger,

Thanks for your input. I have just tried reseating the video card (and removed a lot of dust from the fans) but this doesn't solve the problem. Still no signal from computer to the monitor. With no video card, I don't get any error beeps. Does that help the diagnosis? The computer is over 5 years old so not exactly new, so if getting a new video card doesn't guarantee a fix, perhaps I need a new machine?

cheers,

Nick

#8 rotor123

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Posted 19 January 2013 - 06:25 PM

Hi, Let me put it this way, if You have the Internal speaker hooked up and you were getting the Single beep everytime you started the computer then removing the Video card should have caused several beeps.

This will only work if the internal speaker is hooked up to the 4 pin connector on the motherboard.

While You have it open take a look at the Motherboard and see if You have any bulging capacitors. They should be flat and no leaks.

This page has some examples of bad ones.
http://en.wikipedia.org/wiki/Capacitor_plague

If so let me know

Thanks
Roger

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#9 zeta2reticuli

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Posted 20 January 2013 - 02:44 AM

Thanks for your help Roger. Well, I can't see it on the motherboard (not sure what I'm looking for) but I'm pretty certain that the internal speaker is connected because (i) I have heard it working recently (after another problem, subsequently fixed, that sounded beep codes), and (ii) nobody has removed it. Nevertheless, I don't get any beep codes, whether the video card is in or out. Tried another reseating of the video card, but still no signal to monitor...

The motherboard looks fine to me, no bulging capacitors or obvious damage anywhere. Would be grateful for any ideas...

Edited by zeta2reticuli, 20 January 2013 - 02:46 AM.


#10 rotor123

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Posted 20 January 2013 - 12:24 PM

Hi, No beep codes means something affecting the motherboard or the motherboard itself.
I presume the Fans run when you turn it on? Or the power light on the computer lights up?

Try taking out any add on cards. Unplug any USB devices.

Do you have a voltmeter and know how to use it? If so We check the Power supply next.
From DC3

Reading PSU Rail Voltages

Caution: Please read this before continuing.


• Since it will be necessary for your computer to be on during this procedure, you need to be aware that you will be working with live 12Volt DC potentials, which if handled improperly may lead to electrical shock.

• There are electronics inside the case that are very susceptible to electrostatic discharges. To protect your computer, touch the metal of the case to discharge yourself of any electrostatic charges before touching any of the components inside.

• If you are not comfortable doing this procedure, then I would suggest that you not use this tutorial. The risks involved are minimal, but are there nevertheless. Anyone who uses this tutorial will be doing so at their own risk.


There are two devices commonly used to read the rail voltages: a PSU tester, and a multimeter.

The PSU tester is the easiest to use since all that is necessary is to plug the different connectors into the tester and read the results on the LCD display. The problem with most of these is that they only perform a pass/fail test. They will not provide you with actual voltage readings.

There are a variety of multiple meters, but this tutorial will address Analog and Digital multimeters. The advantage of these meters is that you will be able to obtain accurate real time voltage readings.

For those of you who wish to know more about multimeters there is an excellent article in Wikipedia.


Analog Multimeter

Posted Image


An Analog multimeter is a little more complicated to use. Both Analog and Digital multimeters need to be set to the appropriate voltage, but with an Analog multimeter, you will need to choose the voltage range and must read the proper scale.

The Analog multimeter uses a needle display which moves from 0 across the scale until it reaches the voltage being tested. This multimeter has five major linear divisions with multiple scales to read a variety of ranges. An example would be three different ranges. The first is graduated in increments of 0 through 5, the second, 0 through 10, and the third, 0 through 25. Each of these ranges are subdivided into divisions that are graduated into tenths. In order to read 12 volts the 0 through 25 range would be the appropriate one.

Because DC voltage has positive and negative potentials this device is polar sensitive, this means that if you reverse the two probes when reading a positive DC voltage it will read as a negative voltage. This is actually necessary to read negative DC voltages. The two probes are differentiated by their color, Black (negative), and Red (positive). To read a positive DC voltage, the correct probes must be used with their corresponding potentials (positive to positive and negative to negative).

With the probes being used normally to read a negative DC voltage, the needle moves from the 0 to the left, "pegging" the needle. By reversing the probes you can properly read the negative voltages.

Digital Multimeter

Posted Image


The Digital multimeter (DMM) is much simpler to use. As was mentioned previously, you will need to set the appropriate voltage. One of the advantages is that the DMM has an LCD display with a numeric readout, so there are not any multiple scales to read. Another advantage is that most DMMs are autoranging when reading voltages, which means that you will not need to set the range with these DMMs. A DMM will read both positive and negative DC voltages and display them correctly. When reading a negative voltage, a minus sign will appear on the display before the numeric value. This still is a polar sensitive device, so you will still need to use the positive and negative probes with their corresponding potentials.

There are five different DC rail voltages which are color coded. The Black wires are always negative.

Yellow +12VDC

Blue -12VDC

Red +5VDC

White -5VDC

Orange +3.3VDC


There are only three voltages that can be measured easily without disconnecting the 20/24 pin connector from the motherboard: +12V, +5V, and +3.3V.

The +12V and +5V voltages can be read from a four pin Molex power connector.

Four pin Molex power connector

Posted Image


The same voltages can be taken from a four pin SATA power connector, but in order to read the +3.3V you will need to read this from a five pin SATA power connector as seen below.

Five pin SATA power connector.

Posted Image

To read these voltages you will need to insert the Black (-) probe into any of the black sockets, and insert the Red (+) probe in the different colored voltage sockets. To read the voltages from a SATA power connector it is easiest to insert the probes into the back of the connector where the wires enter. Unfortunately the sockets of the modular SATA power connectors are not accessible from the back, so the readings will need to be made from the socket side. Some probes are going to be too large to fit in these sockets, so you may need to insert a piece of wire into the socket of which you want to read the voltage of and place the probe on this for your reading. To reduce the potential of creating a short I would suggest taking the ground potential from another connector so that the two wires will remain physically separated.

Caution: It is very important to make sure that you don't allow the two probes to touch each other when taking the voltage readings. This will cause a short which could damage the PSU or other components.

To get accurate readings of the rail voltages it is important that there be a load on the PSU. In order to do this I would suggest downloading Prime95 for this purpose. This program was designed to be used by overclockers to put a full load on the RAM and CPU to determine the stability of their overclocking. Because of this it will put stress on the CPU and RAM which will create higher than normal temperatures. For this reason I would suggest not running this program any longer than is necessary. I would also suggest that an inspection be made of the interior of the case to make sure that there isn’t an accumulation of dust which would impede adequate cooling. Pay special attention to the heat sink and fan assembly on the CPU. If there is a dedicated graphics card with a fan installed on it, look at this fan as well.


Readings should not have variances larger than +/- five percent.

Maximum.........Minimum
12.6V.................11.4V
5.25V.................4.75V
3.47V.................3.14V


One change is that I would read the voltages at the 20/24 pin plug with it plugged in and turned on for the orange lead as the SATA plug is hard to use for a reading and could cause damage to other components if done wrong. The four pin Molex is safe to read from.

Any missing Voltage could be Your problem. Except that the 20/24 pin plug may be missing the white wire, if so no problem.
Yellow +12VDC

Blue -12VDC

Red +5VDC

White -5VDC

Orange +3.3VDC
The easier test is using a known good power supply if you have one handy.

Good Luck
Roger

Edited by rotor123, 20 January 2013 - 12:26 PM.

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#11 zeta2reticuli

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Posted 20 January 2013 - 04:11 PM

Thanks Roger. Unfortunately I don't have access to a voltmeter. There is no obvious sign that there is anything wrong with power, in absence of doing the tests that you recommend. On turning on the computer, the fans and lights all come on. There is also a yellow LED on the motherboard which is on when the power cable is connected to the computer. I have removed all USB devices and there are no add-on cards. cheers for your help,

Nick

#12 rotor123

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Posted 20 January 2013 - 09:08 PM

It seems as if it must be Motherboard or Power Supply, 99% chance.
Without measuring all voltages or substituting a known good Power supply I don't know how to pin it down any better.

Good Luck
Roger

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#13 zeta2reticuli

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Posted 21 January 2013 - 03:03 AM

Thanks Roger, you've been really helpful. Sounds like I might have to make a new investment. Will get it checked out locally.
Nick

#14 zeta2reticuli

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Posted 22 January 2013 - 09:12 AM

I took the machine to a local computer repair store and they told me that the video card had failed, so that seems to have been the issue.
Thanks to all for the help!

#15 rotor123

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Posted 22 January 2013 - 11:11 AM

Is it working now? It makes me wonder why pulling the video card didn't make the no video card beep, Unless the motherboard had built-in video too.

Thanks for the feedback
Roger

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