Testing VRMs

[momaka]

Re: Testing VRMs

i need complete startup process of desktop motherboard
please help

Check all power rails first and make sure they are what they should be. Usually it's at least the following:
CPU V_core (a.k.a. CPU Vcc)
NB Vcc (typically less than 1.5V)
RAM Vdd/Vddq (2.5V-2.6V for DDR, 1.8V-2.1V for DDR2, 1.35V-1.5V for DDR3)
RAM Vtt (half of RAM Vdd/Vddq)
SB Vcc (1V-3.3V)
and possibly a few intermediate rails.

Boards with an AGP 2.0 or 3.0 slot will also have a separate rail that is typically either 1.5V or 0.8V respectively.

[ajsurkhi]

Re: Testing VRMs

I have ASUS M2N68 PLUS Motherboard. When i connect power supply cpu fan start for second and then stop. After pressing power switch nothing happen. Power switch have 0.4v only, vrm section has not getting any power. some one says SIO chip is faulty.
any body have an idea.?

[ajsurkhi]

Re: Testing VRMs

i need complete startup process of desktop motherboard
please help

[alihomee]

Re: Testing VRMs

Procedure for testing Voltage Regulator Modules (VRMs):
(This assumes that any bad capacitor problems have already been fixed.)

1. Turn off power to the computer.

2. Remove CPU, memory, and all peripherals from motherboard. Disconnect power supply.

3. This step verifies that the board is not damaged, and the VRM is not shorted:
a. Measure resistance from power supply pin (+3.3, +5, +12, -5, -12) to input of VRM. Resistance should be zero (too low to measure).
b. Measure resistance from output of VRM to load supply pin. Resistance should be zero (too low to measure).
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).

4. Install CPU, memory, and all peripherals to motherboard. Connect power supply.

5. Turn on power to the computer.

6. This step actually tests the VRM (all voltages taken with respect to circuit ground):
a. Measure voltage at the power supply side of the power connector (+3.3, +5, +12, -5, -12).
b. Measure voltage at the motherboard side of the power connector (+3.3, +5, +12, -5, -12). Anything less than the value obtained in step 6.a indicates a high resistance in the power supply connector.
c. Measure voltage at the input to the VRM (+3.3, +5, +12, -5, -12). Anything less than the value obtained in step 6.b indicates a high resistance in the PC board traces to the VRM, and is probably not repairable, even with a schematic.
d. Measure voltage at the output of the VRM. The value obtained depends on the functions being powered by the VRM, so knowledge of the expected value is required. Anything different than expected indicates a failed VRM (note that output may be higher or lower than expected if bad).
e. Measure voltage at the device being powered. This requires knowledge of the device (which pins are power pins). Pinouts are readily available on the Internet for 30-pin, 72/144 pin, and 168 pin memory, as well as ISA, PCI, AGP, USB, etc. Pinouts for CPUs are either on the Internet or may be obtained from the manufacturer. Anything less than the value obtained in step 6.d indicates a high resistance in the PC board traces from the VRM, and is probably not repairable, even with a schematic.

so where i found the input of vram

[styxbound]

Re: Testing VRMs

And thanks for that, PCBONEZ. Certainly should help me figure it out.

[PCBONEZ]

Re: Testing VRMs

Sorry, I'm old and senile. Can anyone simplify for me how to find the inputs and outputs on vrms? There seem to be any number of fets around the cpu on a lot of boards, and I can't figure out where the in and out is on the circuit.

'In' will have +12v connected one one side of caps.
[Continuity check to power plug.]

'Out' will have Vcore on one side of caps.
[Continuity check to toroid(s) NOT connected to +12v.]

.

[styxbound]

Re: Testing VRMs

Thanks, PyrOBEAST, I'll see if I can properly apply that to some boards.

[Pyr0Beast]

Re: Testing VRMs

Ouput is past the choke on output capacitors
Input on input capacitors

[styxbound]

Re: Testing VRMs

Sorry, I'm old and senile. Can anyone simplify for me how to find the inputs and outputs on vrms? There seem to be any number of fets around the cpu on a lot of boards, and I can't figure out where the in and out is on the circuit.

[cmosbios]

Re: Testing VRMs

@Akor
you mean if I test the VRM, test each mosfet(VR) inputs and outputs? I am not sure if you are referring to VRM block (2 mosfets, ic driver, pwm) input and output circuit tests. what i know about the VRM is NOT the mosfet itself but the circuit. please enlighten me.

[cmosbios]

Re: Testing VRMs

well you can use hot air rework station for reflow.

[Zero Hour]

Re: Testing VRMs

I suggest sir as a last ditch effort before retiring it completely if it's not too late, baking the board. I have the problem as a common issue with geforce 6100/6150 chipsets. It's the closest I can get easily to a 'bga reflow' since I don't have a heat gun or a torch or patience. I know it's not a 'convenitonal' method, but for a board you've attempted everything else on and are set on pitching it, it can't hurt.

My method, strip the board of any heatsinks and battery and cmos chips if possible, remove all thermal paste and thermal pads, preheat oven to 384F, elevate the motherboard off of a pan (i ball up aluminum foil and leave a little pointy end for 4 mounting holes to support the board) and bake for 5 minutes. I don't suggest pushing past 6 minutes, it's never been beneficial in my cases and stinks like hell >.< But so long as you can vent the house afterward hey it's fun :P

Or if nothing else, I'd pay shipping on the board if you don't wanna go through the trouble of baking it

[Pyr0Beast]

Re: Testing VRMs

Replace the board. Simplest and effective.

[ivanlee05]

Re: Testing VRMs

I think this is a chipset problem that I could not repair anymore... I went to test all the electrolytic capacitor, and all does have more or less same voltage as input voltage...

I have no time to check all the surfaced mount resistors, diode and capacitors... I'll just force him to buy another Motherboard...

His motherboard served him well for almost 3years...

R.I.P. Biostar "RedFox" GF7050V-M7 SE

Bought: 09/10/07
Died: 01/29/10

^_ _^

[ivanlee05]

Re: Testing VRMs

I am having problem with my neighbor's PC... His motherboard (Biostar GF7050V-M7 SE) could not boot... It has a power but theres no display or even beeps... I already check all of the VRM mounted in the Motherboard, all does have output voltage that range more or less what the input voltage is...

My first tought was a Failed BIOS updates... But He doesn't even know how identify a computer parts... I still had to recover the BIOS thru AMIBOOT.rom BootBlock Recovery... No, the problem is not the BIOS...



Other components like ram, psu, hdd, odd and the processor has been verified in my PC except for the video card... He doesn't have any, He uses the Onboard Video...

Thanks for those who will reply...

[Pyr0Beast]

Re: Testing VRMs

Check the output voltage then.
(With the component in place of course)

[ivanlee05]

Re: Testing VRMs

?
Source = Output
Drain = Input
Gate = Gate

Current flows from the Drain to the Source afaik. (When the gate is (ON))
Can also flow backwards once the gate is on, however, the body diode will conduct when the gate goes off, leading to rapid heating.

thanks sir for the explanation sir... i have a motherboard with no power here, i already check every parts like processor, memory and psu, they are good.. i'm suspecting dead vrm...

[Pyr0Beast]

Re: Testing VRMs

?
Source = Output
Drain = Input
Gate = Gate

Current flows from the Drain to the Source afaik. (When the gate is (ON))
Can also flow backwards once the gate is on, however, the body diode will conduct when the gate goes off, leading to rapid heating.

[ivanlee05]

Re: Testing VRMs

Source = Input
Drain = Ground
Gate = Output

[Pyr0Beast]

Re: Testing VRMs

Laptop motherboards ... hmm.... if I have the time ...

//c. Measure voltage at the input to the VRM (+3.3, +5, +12, -5, -12). Anything less than the value obtained in step 6.b indicates a high resistance in the PC board traces to the VRM, and is probably not repairable, even with a schematic.//
Is repairable, by making a bridge with a wire. Usually from one capacitor to the next one. Never occurred to me unless it is a manufacturer design.

Basically, it is pretty simple. If mainboard does not POST, check voltages.
If PSU voltages are within range, check voltages on motherboard. Cpu has pretty much standard voltage. About 1.4V is fine for newer CPUs, 1.8V for athlons and P3's, 2V or greater for first celerons and P2 (Some early P3)
If there is no power (voltage) to the CPU, check if you placed capacitors the right way, observing the polarity. Same goes for other circuits, RAM, AGP etc. ..
If VRM IC is busted, it would be hard to find a new one. Sometimes (rarely) only one of the mosfets break, usually the upper one. When it does that, the lower one migh go 'poof' as well (protecting the CPU).
If one breaks, replace both. Check IC for damage, might be good to replace that one as well, sometimes it is the cause of this mess.

//VRMs (voltage regulator modules) are a specific class of MOSFETs; //
Far from being true. A VRM module consists of the controlling IC and MosFet's (if we focus only on semiconductors).
However, it is true that there are many type of FET's. Mosfet being the most common one. JFET is one of the other type.