Testing VRMs

[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 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

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

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...

[bianchi77]

Re: Testing VRMs

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

[budm]

Re: Testing VRMs

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

[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.

[bianchi77]

Re: Testing VRMs

yes 35 ohm without CPU.....now 35 ohm only from those small capacitors below the CPU...
do you reckon one or some of them are faulty ? because from my experience...ceramic capacitor never give me a very low resistance....

Have you got one before with SMD MLCC faulty ? overvoltage and overheat from the CPU I reckon ....

[budm]

Re: Testing VRMs

BTW, you never tell us what dcv you were getting at the output of that power supply.

[budm]

Re: Testing VRMs

cearamic capacitor never give me a very low resistance: when they fail they will short out or have very low resistance. MLCC cracked easily.

[budm]

Re: Testing VRMs

BTW, do you other mother board that you can check the resistance of the Vcore and GND?

[bianchi77]

Re: Testing VRMs

From 7 caps I have taken off....value = 5uF and resistance is on level M ohm until OL...
which normal....character of charging of capacitor...I have another 16 to 18 caps to analyze now...hmm...abit fiddly...small on the bottom of the CPU....

[bianchi77]

Re: Testing VRMs

34.5 ohm photo....without cpu 34.5 ~ 35 ohm....don't worry it's nearly the same...

[bianchi77]

Re: Testing VRMs

I measured from other working motherboard...even lower from Vcore to ground = 2.1 ohm with CPU....

I have a doubt if it's ceramic caps problem....I suspect I have problem with my buck controller....it's generating voltage more than the CPU needs and shut down...

[bianchi77]

Re: Testing VRMs

I'm thinking for unsoldering NCP5322 and see what's the response without that chip...
another test...

[bianchi77]

Re: Testing VRMs

NCP5322 unsoldered...

[bianchi77]

Re: Testing VRMs

I've tested just now without NCP5322 and CPU on it....it's running stable not suddenly off...all FETs,Caps and inductors on it....
I'm waiting for my NCP5322 coming now....hopefully it will answer my question

[momaka]

Re: Testing VRMs

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

In my experience, CPUs and GPUs always measure low resistance, typically under 10 Ohms. So the reading bianchi77 got on the CPU output isn't indicative of anything wrong at all. Now, if he removes the CPU he *may* get a high resistance reading of a few hundred Ohms to a few KOhms, *IF* the Northbridge doesn't use CPU V_core for its power (which is the case only with only *a few* motherboards).

[bianchi77]

Re: Testing VRMs

I removed CPU resistance to ground = 34.5 ohm...do you mean northbridge sharing the same Vcore ?

[momaka]

Re: Testing VRMs

Is it possible that one of the ceramic caps near the CPU is short ? ( on the bottom of the CPU, inside the socket )

Possibly, although I have seen only a few short out with such a high resistance (34.6 Ohms without CPU in socket). Most go short-circuit like a piece of "wire" (i.e. sub-1 Ohm)

without CPU in socket, 34.6 ohm...

Any thick traces going from CPU V_core to Northbridge? If yes, that means the NB is powered by CPU V_core as well, and that's what would be giving you the still-fairly-low resistance of 34.6 Ohms.

I have removed all the output capacitors now....I got only 8 ohms between Vcore and GND...CPU in socket...

If you are trying to find a short-circuit on CPU VRM, *ALWAYS* remove the CPU from the socket. Otherwise the CPU will give you a low resistance reading and you will never know where the short-circuit is coming from.

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?

Could be his multimeter, if he is using a cheap one. I know my Harbor Freight meters will sometimes show 1 Ohm with shorted leads and other times up to 3 Ohms, depending if I don't play with the rotary dial.

That's why I never take it for granted that anyone here is using perfect test equipment. Always watching out for "weird" and "off" measurements.