Author Topic: Low Voltage Failure of Power Unit (switched mode) fix  (Read 583 times)

spiyda

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Low Voltage Failure of Power Unit (switched mode) fix
« on: May 26, 2017, 12:20:32 AM »
This has been covered in an old post,   "Re: RV4S Camera Problem"  but I'm posting it here under this title as it will be easier to find in a rush if the same happens to you


 I've just had the same problem so to confirm...

Schottky Diode ( D3 )  gone short circuit on the main main circuit board of the power unit that has switched mode power supplies.

the giveaway is that all the low voltage stuff stops working ( cameras, fans, air pump etc. )  but the heatsink on the 2576 is still warm to the touch

It was the diode that is across the output of the LM2576 which drops the 36V down to 12V.

I assumed wrongly that the 2576 would be cooked by this, but it seems it has sufficient protection to withstand a short circuit almost indefinitely..

I replaced the IR80SQ045    (8A 45V diode)   with an MBR3060CT   (dual common cathode 30A 60V)  which is a completely different package
because its all I had that was big enough..

don't be tempted to use a standard silicon diode, it won't work !

Oh, and in an emergency, for speed, you might be able to cut the old diode and solder the new one to the leads without taking the board out