Help! Voltage injection not working

[doncius85]

Hello!
Need help. Have two different dead laptop motherboards. One has a short on 3V rail, so I'm injecting voltage right there and it draws 8A, but nothing gets hot. Another board has a short on one of the mosfets. When injecting voltage, it draws 7A and the board is dead cold too. I'm inspecting using a thermal cam. What can be wrong? Where does those amps go? Since my power suply has a short circuit protection, for voltage injection I'm using Ni-MH battery, could this be a problem?

[reformatt]

Re: Help! Voltage injection not working

Take the heatsink off the CPU and retest. Most shorts of this nature are the CPU/PCH

[CapLeaker]

Re: Help! Voltage injection not working

if nothing is getting hot, the something is heatsinked pretty heavy...

[petehall347]

Re: Help! Voltage injection not working

about 24w then 0.375 ohms . at 3v .

[doncius85]

Re: Help! Voltage injection not working

Heat sinks removed, CPU's not getting warm on both boards. One board reads 0.1Ohm and another 0.2Ohm short. What's strange on the second board, that I'd say 30% of the mosfets reads 8Ohms Source to GND... Is that normal?

[reformatt]

Re: Help! Voltage injection not working

I'd suggest getting something like the Mechanic TS-30A short killer in combination with a thermal camera. Voltage is selectable, and it will pulse on and off when a short is detected. So when a thermal camera is used, it makes the source of the short quite obvious without damaging the board in the process.

Don't go above 1V when doing voltage injection. If you have a high side FET shorted in a buck converter for the PCH/CPU/GPU, any volts you inject will end up directly to said components.