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Flashing Keyboard Lights

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by jimdale

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I have flashing keyboard lights when I power up the power supply on my P4 motherboard. I have also seen this on other computers (AMD K6, P3). I think a bad video card was the problem on one computer but I can't remember. I know the video is good on the P4, also the memory is good. any suggestions will be appreciated!

11 replies

by oz_media

I assume that this is the NumLock and CapsLock lights that are flashing.

This osund to me like a keyboard issue, if it is a keyboard with programmable buttons or scroll wheel etc. You will probably find updating the keyboard drivers will work.

If you are saying the computer doesn't boot and the keyboard lights flash, you may want to remove cards to see if they are dead, NIC, SOUND, GRAPHICS etc.

by jimdale

ok, let me go a little further: the numlock, caps and scroll LEDs flash repeatedly before the computer is started. It has happened on more than one board with a working keyboard. These boards are not from the same manufacturer, nor are they the same generation (i.e. pentium, PII, P4, socket 5, socket 7. etc...) The memory is not the same between boards, the video cards are different. I have tried removing all cards and disconnected everything and still no luck except in the one instance stated before. The power supplies have all been different and work. This problem occurs before anything thing else happens, no POST, the computer never starts. I have used a POST testing card and the voltage LEDs flicker but then nothing. The boards never power up. Sorry for not being more in depth earlier.

by oz_media

Sorry mate it's over my head, if you've tried removing/swaping RAM, tried RAM in different sockets and removed cards, checked power supply etc. I'm lost. Your reponse isn't on this screen, did you say you'd tried different keyboards or just mobos I assume you would havetried swapping keyboards of you've swapped everything else?

Other than the above, the only thing I can say is look for an answer from The Chas or Coluck.

by thechas

The keyboard lights flash once as a normal part of the power on sequence.
Basically, this is the POST test for the keyboard controller.

On an ATX style PC, the basic power up sequence is as follows:

Pressing the power switch initiates a signal from the motherboard to the power supply that tells the power supply to turn on.

When the power supply turns on, the individual devices begin their self tests.

When the CPU powers up, it sends a signal to the power supply that everything is good, and to continue to supply power.

What is happening on your systems is that one or more devices are having problems and cause the power good signal to not be sent from the motherboard to the power supply.

It could be the CPU, the motherboard, or ANY connected device.

Just over a year ago, there was a problem that affected a number of motherboards. They were assembled with a batch of bad capacitors.
These caps leak or even explode.
Most motherboard manufactures did not acknowledge that there was a problem.
They quietly replaced those that failed during the warranty period.

As far as what to do, remove your plug-in cards, and give the motherboard a thorough visual inspection.
If any of the capacitors (blue or black and silver cylinders) are bulged or leaking, that is the problem.

If the caps look good, start with a basic system (CPU video and RAM) and see if that will boot.
If it boots, add devices back in 1 at a time until you find the device that is the problem.

Chas

by jimdale

Thanks for your answer but if I'm not mistaken,. the power good signal comes from the power supply to the cpu. I believe it is the orange wire on AT power supplies but I'm not sure as far as the ATX ps is concerned, I'll have to check the pinouts. And I have already inspected the mobo for bad caps. The caps you are referring to are usually in power circuits versus signal circuits which could also be the problem. There are also surface mount caps that could cause problems. Without prints of the boards I could be checking caps for a very long time. Thanks for the info but I am having similar problems on several mobos from several manufacturers.

by cglrcng9

Hmmmmm, Chas has me w/ eyes wide open as I have a Dell board that was out of warranty and I found a blue capacitor to the rear of the mobo that was leaking & buldged. Any documentation you can give on that problem Chas? I would sure like to get the board replaced by either the manufacturer or Dell.

BTW, that board was causing the same exact thing to happen as described by this poster. Lights flashed no post up. I did everything then a detailed out of box inspection and found that leaking cap and knew the board was toast, but I didn't know it was a man. defect due to a bad capacitor problem that has happened en masse. See they do fool us sometimes. I want to know why it isn't a crime though?

by jimdale

This is for Chas, I checked some of the caps on the board and found several that registered low resistance. I have also found that these caps all share the same ground so I assume they are all on the same circuit but I'm still not sure which on is pulling the circuit down. I guess my next step is to remove them one at a time until I find the bad one. I want to apologize for not accepting your answer because it did help after I checked the board that I am currently working on. If there was a way to award the points to you I would. Your comment does seem to point me towards the problem. Thanks.

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