differentiate between a cristal OR C problem and a microcontroller probl

Thread Starter

patpin

Joined Sep 15, 2012
388
Hello,
I have a motherborad that doesnt react to the powerbutton. It is managed by a KB3926 C0 . The powerbutton input goes to zero at the KB but the expected output is not present. Power at the KB is OK. Grnd too.
I checked the clock over the X0 of the cristal and every second or so there is an interruption (Picture; voltage has to be *10).on the 32K signal, which is not present on another identical functioning MOBO.
My question is. Can it be the cristal or the C's around it or is it the KB itself. Can one differentiate here?
 

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Thread Starter

patpin

Joined Sep 15, 2012
388
OK, I'll explain a bit more. Measuring the outputs and inputs of the KBC chip (keyboard and power controller etc) I found that the powerbutton signal is goiing low (should be like that) but PC is not starting. Normally this KBC chip is activating a lot of other chips of the motherboard. In my case this signal is absent, so I suspect the KBC to be the cause, but before trying to replace it I want to be shure that no other components around it are bad. One of them is the cristal 32KhZ and 2 27pF capacitors. Thats why I looked at the X0 pin of the cristal in order to see the clock signal.
On a well functioning mobo this is a simple sinus wave of 3.6V and 32 Khz. , but on the bad one I have a signal that is interrupted (goes to 0V) every second) (picture post 1). This patters repeats without manually doing anything
My question is. Is it certain that this phenomen is caused by the KBC chip or can the cristal or the caps be the cause that a microcontroller chip doesnt function.
 
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Ok, remember, I am just trying to help...My answer is "No". That is, it is NOT certain that this phenomenon is caused by the KBC chip.

But, it does not seem to me to be an either/or situation, so I don't think it follows that "or can the cristal or the caps be the cause that a microcontroller chip doesnt function."

IF (and that word is intentionally in all caps) I am understanding you correctly, what you are calling the KBC (KB3926 C0) is a super I/O controller and I would think (and I honestly don't know) that the problem could be due to many other reasons than a crystal failure. Is there a particular reason that you believe so?

On the other hand, it would seem to be to be relatively easy to replace the crystal...no?
 
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philba

Joined Aug 17, 2017
960
You said power at KB is OK. Ground too. Does the power to the motherboard come on? You have to measure it at the motherboard. The computer "power button" isn't a switch that lets the power in. It's a signal to the PSU and is powered separately.
 

Thread Starter

patpin

Joined Sep 15, 2012
388
You said power at KB is OK. Ground too. Does the power to the motherboard come on? You have to measure it at the motherboard. The computer "power button" isn't a switch that lets the power in. It's a signal to the PSU and is powered separately.
Yes all powers necessary (when PC is off) are present: 19V and 3VPCU and 5VPCU.
 
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