Mesa card 7i76e no longer has +5v

The card and cnc hardwares used to work well for almost a year. Yesterday, when I power on, I found error message that ethernet connection dose not reach. Looking at the card, the orange LEDon field power area side  lights up but but not for the red one on logic side. The card used to have one 12VDC voltage supply for both the field power supply and unregulated power supply (on TB3 for logic side) use. When I measure all the TB2 and TB3 +5V output sockets, they show only 1.7V. I detached the unregulated power supply for logic side and use individual 5v power source to P3 socket, the red LED just dimmy flashs. I measure the P3 connectors voltage, it went to zero. I detached the power source and measure P3 resistance, it is 12 ohm, it seems not reasonable. Are there something already dead?

If this is a C rev card, it may be that the 5V TVS clamp diode has been damaged
by an overvoltage. This would show up as a 5V short.

Thanks for the quick reply, attached are two photos of the board. Could you show me which one is the said TVS diode? what description or spec. of it is? Can i get one in market?

That's a REVB board with no 5V TVS, Not a lot of parts run from the 5V,
mainly the step/dir drivers you might try a lab supply or other 5V supply
limited to about 2A and see what gets hot if left on for a bit.

Last time, when i powered on machine and found that the failure in ethernet connection, I also found that, in computer side, the properties of network card all set to disable, i checked through Windows enviroment as it is dual boot system, i turn them on manually.
Afterwards, in Linux conditon, the 7i76e card still cannot be connected, then I found the cards' +5v power failed. Did it damage by high voltage surge throught internet connection? When i checked the X, Y, Z axis drivers control box, their normal green LEDs still lit, they don't have problem and would not be the issue to cause the failure in Mesa card. Afterward, i pulled the card out from the controller enclosure box and used individual +5v power supply to input the logic side for checking, the result as listed previously. It is a mobile phone wall plug 3A charger, the PWR failed indication LED on Mesa card flashed only a short preiod of time and turned off completely, zero volage was measured to input to logic side, no hot or warm components can be observed. Would the mirco-controller chip already failed?

+5v and 3.3A current draw was measured from wall plug power charger to the card, but i don't know where the power gone, as i touch on components by finger, i can't find out hot or warm area, I don't have infra-red camera to shot the hot spot area. Zero voltage was measured on JTAG jumper's 3.3V pin

Make correction in my mentioning lastly, i) actually the wall plug power charger delivered almost zero voltage when it was input to the card, althought the current draw shown was 3.3A . ii) there was a power grid in my town shutdown lately, may be there was voltage surge that caused my computer internet card shut down automatically and the mesa card failed (?)
I don't have proper lab supply, but i will try to input +12v to unreg logic PWR +IN on TB3 to investigate again. On the other hand, shall i directly input +5v to TB2 stepper drivers' +5v socket pin to investigate (ie which components get hot)?

No if you want to test with a 5V supply, apply it to P3.
Where are you located? It may be easiest to return the card for repair/replacement

Yes, the charger cannot supply more power. There must be a hot zone. You can try a little current for more time.

>Understand. Up to now, I only input +5v to P3 or +12V to unreg logic PWR +IN for testing. Neither of them have obvious power draw, the former one almost went down to 0v but having current draw 3.3A, the latter one 12v having 0.05A current draw(no 5v output from it going to logic portion is observed). Getting hot components cannot be found in the process.
>I live in Hong Kong