LED driver boost converter blown

[MarkC1970]

I have an LED boost circuit that is faulty.  The FET (AOD458) and the rectifier diode (SR320) were both short.  I replaced them both as well as the input and output caps.

Applying power to TV gets me the standby light and 55v but the instant I power the TV up the FET smokes and is dead again.  I think the coil is short as well because it reads just 0.09 ohms. 

My understanding, limited, is that the FET in a boost converter grounds and releases the coil momentarily and the EMF this generates in the coil results in a voltage spike on release that is passed through the rectifier diode and stored in the output capacitor. 

The rectifier diode is dead again as well and so I am a little confused.  If the coil is short the current through the FET would be massive when the Gate is triggered and I can see why it would die again but why would the rectifier diode die again, it isn't seeing massive current or voltage?

When I started repairing TV's we literally had valves and so an old dog is trying to learn new tricks here.  Any pointers would be much appreciated.

The boost controller is an OB3350CP and the board is a TP.MS6486.PB711.  I can't find a schematic but I would be grateful for a link.

Thanks all...

[TheMG]

If it indeed is just a simple boost converter, perhaps the output is being overloaded. Boost converters can't output a voltage any less than the input voltage to the boost converter, and thus can not offer overload or short circuit protection.

Have you checked the LED array to make sure it's good? A large number of shorted LEDs could create such a situation. Although normally most TVs would have a more advanced LED driver which would have the ability to disable output to the backlight completely if out of spec.

[thinkfat]

Have a look at the datasheet of the OB3350CP. You can assume that the circuit in the data sheet is identical to the one in your TV. If the rectifier is blown, too, it's a given that the LED strip has a short circuit.