Searching equivalent part of this old ST component

[msergencatal]

Hi everyone,

I am searching old ST component that placed on PCB of my old Braun trimmer. The part name is "D6 16A F 122" I also shared the picture of PCB. I can not find the datasheet so I don't know the specifications of this component. I want to change this broken part with equivalent component. I think this is a MOSFET with 16A but I am not sure. The gate voltage level is also is important. Can anyone help me to find this specifications? Or suggest a component which is available? 

[Peter BENSCH]

Typically, these flyback or buck are quite easy to redraw from the circuit board. Presumably this can be used to estimate the power of this device. Under no circumstances does "16A" stand for the current, it should be the marker instead, but I have no entry for this in my list. It’s probably a custom device and can also be an npn bipolar transistor.

How do you know that this device is defective? In the event of an overload, the fuse resistor that you can see in the picture at the back left should have burnt out?

Regards
/Peter

[msergencatal]

Hi Peter, thank you for your reply firstly. I tried to draw circuit and share below. This is a flyback converter as you said. I tested all diodes and there is no short circuit. Fuse is also OK, there is connection. I also measured the DC link voltage. There is DC link voltage on the capacitor. When I tested the npn transistor with multimeter buzzer mode. I obtain the short circuit between gate and source pins. I made all the measurements while the components were on the PCB. This is why I am think the transistor is defective. Am I right or did I something wrong while measurement? 

[Peter BENSCH]

Pretty sure its an npn bipolar transistor, not a MOSFET. You could verify it using a diode measurement between base and collector or emitter.

[JJOOWUUW]

STD616A

[msergencatal]

I removed the transistor and tested the pins with diode measurment as you said. There is short circuit between base-emitter. I am going to change with proper one. Thank you for your help. I ll give info about the result soon.