Thank you  all for the replies

> Does the CPU start, if you reset it while keeping the power on? If so,
> most likely the problem is slow rise time.
I tried to reset CPU several times, but still does not start.But when I use=
 the correct power=20
supply, it starts when resetting.

> Could be some sort of inrush current effect. Also, if there is a
> secondary power supply downstream, it may require the input to have a
> fast risetime.=20
Yes, there are more powers but I reset CPU while keeping power on, so the r=
isetime should=20
be OK.

>Especially if power supply sequencing is important.
Not sure if  the sequencing is important or not, but when I reset CPU(keepi=
ng power on and  =20
using the working voltage supply), it started. So, I do not think, in my ca=
se, the sequence is=20
important.

> Check that your crystal is operating OK. =20
Do you mean the crystal of the mainboard? There is NO crystal that uses the=
 Asynchronous=20
Step-Down Regulator

>Dust/dirt providing a
> leakage path & preventing correct startup?
I hotair reflowed the power supply part already

> Another thing to check
> would be the reset/brownout arrangements - could be on the edge?
Can you explain a little more?
Thanks
>=20

Do you have any other idea?






>=20

> >=20
> > I have a Linux embeded board that  uses=20
> > FP6116 Asynchronous Step-Down Regulator=20
> > a datasheet  is here
> > http://www.micro-bridge.com/data/Feeling-tech/FP6116.pdf
> >=20
> > In this design , that Asynchronous Step-Down Regulator  should
> > supply 1,2V for  CPU  on this board. It worked for some time but now
> > it stopped. So, I measured voltage and that Asynchronous Step-Down
> > Regulator  still supply 1.2V, yet CPU does not start. But when I use
> > a different source of 1.2V, the CPU starts. So, I am rather
> > confused. I can measure the same voltages, and more or less the same
> > spikes( using oscilloscope), yet different results.
> >=20
> > Can anyone suggest any solution to that problem?
> > Thanks
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>=20
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