how to find short in low voltage power rails like CPU or GPU rails

[ktmmotocross]

Hello.
How to easy find shorted component in low voltage power rails like CPU or GPU power rails. i dont have that low voltage and high amperage source to show burning component. How to find for example burned capacitor under GPU or CPU?

[Th3_uN1Qu3]

Re: how to find short in low voltage power rails like CPU or GPU rails

If you don't have such a power supply, build it. You can make one out of a faulty MXM card and a regular bench power supply (or a normal laptop adapter) to power the thing. I can assist with the wiring if you wish.

[rookieme]

Re: how to find short in low voltage power rails like CPU or GPU rails

Interesting theme.
In addition can someone suggest me a proper bench power supply?

[dj_ricoh]

Re: how to find short in low voltage power rails like CPU or GPU rails

Sunday i wanna try a tablet battery.
I keept 2 boards that got a short near the dc entry on a diode.
I left it there because i wanna see if it can heat it up.

Even on psu i use around 3-5v until it pops up.

[ktmmotocross]

Re: how to find short in low voltage power rails like CPU or GPU rails

i have MANY F3/5 board but i must trick the current limiter becauseif it detect short it shut off. i also have many mxm boards without gpu so it will be better solution.

[ktmmotocross]

Re: how to find short in low voltage power rails like CPU or GPU rails

Sunday i wanna try a tablet battery.
I keept 2 boards that got a short near the dc entry on a diode.
I left it there because i wanna see if it can heat it up.

Even on psu i use around 3-5v until it pops up.

5v and 3.3v not a problem just break laptop battery and u have 3.7V cells.

[dj_ricoh]

Re: how to find short in low voltage power rails like CPU or GPU rails

I need to solder a few cells to get the right ampa.

The tab battery alone got almost 4amps when its new so.

I think i still have a big one close to 6?

That will be rly nice to test.

[Th3_uN1Qu3]

Re: how to find short in low voltage power rails like CPU or GPU rails

i also have many mxm boards without gpu so it will be better solution.

Yes. Do you have any nvidia geforce 8400m or 9300m boards? Those are easy to modify.

[Djosla]

Re: how to find short in low voltage power rails like CPU or GPU rails

If you don't have such a power supply, build it. You can make one out of a faulty MXM card and a regular bench power supply (or a normal laptop adapter) to power the thing. I can assist with the wiring if you wish.

This would be intresting,now you made me thinking...i assume you would take the whole power circuit and enable the pwm oscilator ic from external power sources...???

[Th3_uN1Qu3]

Re: how to find short in low voltage power rails like CPU or GPU rails

^^ That's it. You need 8 to 20v input on the main filter caps of the MXM card and a small 5v regulator such as a 78L05 to power the PWM controller originally responsible for GPU Vcore on the card. All you have to do is give it power on the main supply caps. Then you connect the output of the 5v regulator to the logic supply of the PWM and enable signal (EN pin) and it will deliver ~1.2v at 20A or so, fully protected. Thick output wires required, it will melt regular 18AWG wire like found on ATX power supplies.

It's great for finding shorted components - connect on the shorted rail and then feel the board with your hand and you will immediately notice what's getting hot. Since the voltage is low, it will not damage any parts even if the short is on the high side of a VRM and the power leaks thru to a processor or chipset.

[ktmmotocross]

Re: how to find short in low voltage power rails like CPU or GPU rails

yes i have few even with bad gpu so i make some modifications. but what about ilimit and short detection that power off?

[ktmmotocross]

Re: how to find short in low voltage power rails like CPU or GPU rails

there are little more to do than VIN and EN. have isl 6269 on card. must have vin, en, vcc, pvcc. but it giving me 1.7V which is too high. must change Rtop and Rbottom to have right voltage.

but it works

[Th3_uN1Qu3]

Re: how to find short in low voltage power rails like CPU or GPU rails

I already mentioned you will need a 5v regulator for the PWM's logic supply.

1.7v maybe was for memory. That won't have as much current capability. Can you post a photo of the card?

[ktmmotocross]

Re: how to find short in low voltage power rails like CPU or GPU rails

but it was on biggest coil on board. there is one smaller only

[ktmmotocross]

Re: how to find short in low voltage power rails like CPU or GPU rails

here are fotos

[dycc]

Re: how to find short in low voltage power rails like CPU or GPU rails

normally these N mosfet which are responsible for this big current