Testing VRMs

[budm]

Re: Testing VRMs

L2 and L3 are filter output of Vcore for CPU...

Lifting the inductors Lx is to isolate the output section of the power supply from the load to find out if the low resistance is from the power supply or from the loads.

[budm]

Re: Testing VRMs

So you are getting 9 Ohms when CPU is installed and 35 Ohms when CPU is removed?

[bianchi77]

Re: Testing VRMs

L2 and L3 are filter output of Vcore for CPU...

[bianchi77]

Re: Testing VRMs

because there's no short to the ground from that section....with the value 35 ohms without CPU...

yes the low resistance is still there when I remove L2 and L3....
the output is going to the CPU....that section is taken from datasheet so it's not exactly the same with the board....but that's the chip on the board...

I can't measure the resistance of those capacitors with CPU since it's on the bottom of the CPU...

[budm]

Re: Testing VRMs

https://www.badcaps.net/forum/attach...5&d=1473809915
Why don't you concentrate on that section first in the diagram instead of moving to another section?
Where does the output of that section go to?
The low resistance still there ON THE OUTPUT CAPS if you lift L2, L3?

[bianchi77]

Re: Testing VRMs

I do not know what you are referring too, resistors or capacitors. We were dealing with the caps, now you are talking about the resistor values?
09A, 05A are for the resistors.

Yes we are talking about capacitors, but I'm testing the resistors as well near the capacitors while I'm there, curiousity....

I'll let you know the resistance value of the capacitors I've taken from the bottom of the CPU...

[budm]

Re: Testing VRMs

I've found two missmatch value with the code written on it..05A = 110 ohm...measured in circuit 66 ohm...
09A = 121 ohm....measured in circuit 67 ohm....and they are not in parallel...

Could it be the problem ?
Or this one :

I do not know what you are referring too, resistors or capacitors. We were dealing with the caps, now you are talking about the resistor values?
09A, 05A are for the resistors.

[bianchi77]

Re: Testing VRMs

I haven't measured the resistance of that 10uF...I'll let you know...some of them are 5uF
One test that I can do...is, unsolder all the capacitors about 16 small smd capacitors and test the resistance again....

[budm]

Re: Testing VRMs

one of these ? Multilayer Chip Ceramic Capacitor
http://www.ecvv.com/product/2803276.html

It's 10uF...but I got >20000uF on my meter.......another bad capacitors ?

What resistance do you get on that 10uF cap?

[budm]

Re: Testing VRMs

I have removed all the output capacitors now....I got only 8 ohms between Vcore and GND...CPU in socket...I also have removed all the FETs and the resistance is 7.5 ohm....what could it be the faulty now ?????
I have removed the inductors as well so the CPU now isolated by itself....
CPU on socket....resistance = 8 ohm....so it will be some somewhere on the ceramic CPU caps ?
Is it possible that those caps are faulty ??????

Something does not make sense here, you had 9 Ohms before the output caps and MOSEFTs are removed, and now you have 7.7 Ohms, and 8 ohms?
Is Vcore connected to that power supply as shown in the diagram that you are getting the 9 Ohms reading?
Very confusing.

[bianchi77]

Re: Testing VRMs

I've found two missmatch value with the code written on it..05A = 110 ohm...measured in circuit 66 ohm...
09A = 121 ohm....measured in circuit 67 ohm....and they are not in parallel...

Could it be the problem ?
Or this one :

[bianchi77]

Re: Testing VRMs

Photos :

[bianchi77]

Re: Testing VRMs

one of these ? Multilayer Chip Ceramic Capacitor
http://www.ecvv.com/product/2803276.html

It's 10uF...but I got >20000uF on my meter.......another bad capacitors ?

[bianchi77]

Re: Testing VRMs

When I tried to measure one of the chip capacitor with my LCR45....I got value >20000uF
which is not right, mostly those capacitor is about 100nF to 500nF....
Is there any possibilities that they are the faulty ones ??

[bianchi77]

Re: Testing VRMs

I have removed all the output capacitors now....I got only 8 ohms between Vcore and GND...CPU in socket...I also have removed all the FETs and the resistance is 7.5 ohm....what could it be the faulty now ?????
I have removed the inductors as well so the CPU now isolated by itself....
CPU on socket....resistance = 8 ohm....so it will be some somewhere on the ceramic CPU caps ?
Is it possible that those caps are faulty ??????

[bianchi77]

Re: Testing VRMs

that's good news at least something wrong on the output....which one do you reckon ?
Could it be one of the output filter caps short ? but they look ok ( no bulge )...I tried replacing with new one last time...still the same...
Is it possible that one of the ceramic caps near the CPU is short ? ( on the bottom of the CPU, inside the socket )
without CPU in socket, 34.6 ohm...
I'll retry now and see what happen and post it....

[budm]

Re: Testing VRMs

It should be very high in the K Ohms range because the devices (Loads) are not active.

[bianchi77]

Re: Testing VRMs

9 ohms at the output....how much resistance do I expect normally in average?
CPU in socket....

[budm]

Re: Testing VRMs

9 Ohms at the input or at the output?
The Output you will have lots of circuit connected in parallel: loads to GND, filter caps to GND, the Power MOSFETs to GND, so it is the matter isolating the circuit to narrow down where the low Ohms reading is coming from.

[bianchi77]

Re: Testing VRMs

c. Measure resistance from input of VRM to ground (should be greater than 1 megohm, usually much greater).
d. Measure resistance from output of VRM to ground (should be greater than 1 megohm, usually much greater).

I measured it very low at 9 ohm....is it because of filter capacitor in parallel ?
buck controller = NCP5322
Please have a look at the schematic, typical 5322...at the input and output ...there are filter capacitors..
What happen if NCP5322 is bad ? the output voltage is not right ?