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# vdd main short but no heat

so i have an iphone 7 in this morning and as title says i have a vdd main short, wire soldered on and drawing 2 amps but no sign of heat. can i raise the amps and if so what is the max

## 1个回答

Hey Daniel. Looking for a heat signature can be tricky, especially when using a DCPS as the power source. Most bench power supplies offer current limiting protection. That means that when the current reaches the maximum set output, the PS will drop the voltage output in order to maintain the max current.

So when looking for heat, you are essentially hoping some component will give off this heat as a result of power dissipation. However, P=V*I (POWER equals VOLTAGE times CURRENT) through the component. So if your current is 2A but the voltage is essentially Zero (due to current limiting), then the power will be 0W...so no heat!

So the thing to do is either increase the current setting on the DCPS so that there is some voltage drop across the shorted component or use a battery which will not be current limited. The advantage of the DCPS is that you can bring it up slowly to avoid any catastrophic damage by a sudden surge of power.

The other thing to try is to start with a lower voltage, say 2V with a max current setting and then slowly build up the voltage. This can weed out the bad component before fully activating the logic board.

cheers @refectio , think i have burnt the short as when i connect the power lead to dc i wasnt gettin draw now its going upto 0.76 amps. when plugging dc in before pressing the button im getting around 0.16 amps before pressing power. need a new lcd to see if i have image now

@refectio any idea why im getting 0.16amp draw before pressing power

It could be just battery charging...

Battery does nothing. Short drives battery to zero immediately . No current - no heat, so this is not solution.

Also, in my case when you try with DCPS voltage drops to 0.8v / 1A, and 1.6v / 2A again ZERO heat. Same at 3A or 4A.. Just the cables heating up.

@ninos22 check vdd_main or vdd_boost

daniel 将永远感激不已