Pin identification of transistor and transformer from photo of module

Question

From the photos of this driver board (no hands on testing, the photos are all I have to work with), how can one reason-out the E, B, and C functions of the pins (1,2,3) of the transistor, and the coil pairing of pins (4,5,6,7) on the transformer?

Assuming the trace from left side of D5 passes underneath D4, I am thinking 4 and 6 are the output coil since they lead fairly directly to LED terminals.

What is the significance if any of peculiar shape of the hole in the transistor? does it have a function and or indicate type?

(Disregard the red arrow)

The board is discussed in this other question.

Answer 1

? how can one reason-out the E, B, and C... and the coil pairing of transformer?

123 = BCE

1st locate rectifed DC(-) on (7). let's call this gnd. (i.e. 0V)
2nd Pin (1) is connected to 30k (304) and diode to gnd
for BASE reverse clamp. (which also comes from C then 33//33 then (5)
3rd (3) goes to 10R0//10R0 which is emitter needed to raise input Z and limit current.

( thus (2) is Collector to (6) with (4)to storage cap (-).

thus

^{simulate this circuit – Schematic created using CircuitLab}

only specific parts shown

Since oscillators require positive feedback the Base to Collector is opposing dots with B to C inverting to complete the loop.

Answer 2

Resistance measurements, for the transformer. Primary and secondary will be isolated from each other; there may be a centre tap on the primary, etc.

Part number and datasheet, for the transistor. Failing that, diode tester at least tells you the base, and whether it's NPN or PNP. Then the context ... if NPN and one terminal is grounded, pretty good chance it's a low side switch.

The odd shaped hole allows an insulating sleeve around the bolt holding it to a heatsink; the sleeve keys into the slots so it won't rotate when you tighten the bolt.