This has been by far the most challenging ESC to repair. So many components on this device.
It wouldn't turn on. Measuring the power side everything looks fine. Later I found this was not true, because the power board has a 3 mosfet ground switch. Why? The negative battery connector is isolated from the ground on the boards because of this switch. So it turns out one of the low side mosfets on port A was shorted. All the mostfets on the power board is tphr6503pl.
I didn't have a 1:1 replacement but has some AON6512 laying around from another broken ESC.
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| The mosfet closest was shorted between gate, source and drain |
But that was the easy part to find. The bigger problem was the logic board wouldn't turn on.
Usually there is a latch circuit that once you press the ON/OFF botton the circuit would latch the power circuitry until the CPU turns it off via a gpio/transistor.
Going over the main components to investigate:
There is a buck converter which is power by a 12V boost converter. Odd to first boost then buck and the 12V boost doesn't seems to be nearly as powerful as the buck.
A 7805 regulater which is power via a single low power SOT23 PNP transistor. Agains seems odd to have a 2A regulator powered by a 500mA transistor. The transistor may also be a P-channel mosfet. I couldn't find any datasheet for this.
When pressing the ON/OFF switch the base voltage to the PNP transistor is driven low. However the whole circuit wouldn't stay locked meansing powered on. Feeding power directly to the 7805 I was able to turn on the cpu to confirm it was working. If the CPU is bad then the it is a no-fix.
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| Power directly to 7805 turns on the CPU |
The emitter of the PNP is connected to the positive of the battery. The collector did go high but only to around 2V. After check all around I determine that it has to be the PNP that was bad. Replacing with a common PNP it is now working :-)
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| Replaced PNP and fixed solder point |
The componets
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Top side of the power board |
Black: 3 mosfet ground switch
Blue: 3 mosfet high side port A
Yellow: 2 mosfet high side port B
Orange: 2 mosfet high side port C
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Bottom side of the power board |
Small orange: 1 mosfet high side of port C
Big yellow: 3 mosfet low side of port B
Small yellow: 1 mosfet high side of port B
Blue: 3 mosfet low side of port C
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Top side of logic board |
Green: Buck converter LM5148
Blue: 12V boost converter
Red: 7805 5V voltage regulator
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Bottom side of logic board |
Yellow: CPU
Green: Buck converter mosfets and sense resistor
Red: power on latching circuitry