Need help explaining how this circuit works

[laban93]

So i just reverse engineered this circuit board from a failed safety lighting fixture (used when cleaning tanks on ships and rigs), and got it working again after i located and changed a faulty NPN. But i do not understand the working principle of the circuit. It's fed from a 42VAC source, and all the winding taps (1 to 10) is located on the primary side of the transformer. The secondary side has two windings connected to the 36W compact fluorescent lamp (not drawn). Also why is there a "mutual inductor"?

[PKTKS]

Your  draft (assuming you have at least 90% confidence) looks like RCC

RCCs or Ringing Choke Converters are a proper class of ( CHEAP!  very CHEAP! )
self oscillators with a long list of applications

Assuming that as we have no controller IC no SCRs not even MOSFETs

RCCs are designed to induce BJT to unstable operation (aka ringing)
using the transformer coil... several designs possible.

They are  bad, unreliable, error prone and present great deviation
over time.

but they are CHEAP.  Nothing compares.
and they work as long as the choke rings...

BTW some magic voodoos and tricks are necessary to keep
these things properly ringing over time... as components age.

Paul

[james_s]

I think what you are calling the mutual inductor is a common mode choke, it's used to prevent noise generated by the circuit from being fed back into the electrical system where it could interfere with other devices.

[laban93]

Aah, i assumed it was a mutual inductor, both poles are wound around a torodial ferrite core, and a quick google search told me mutual inductor, but i am in no way, shape or form educated in this kind of component repair, so thank you both for helping out! And no, there is no other IC's. I thought the choke usually was on the incoming supply wires? Anyway this is supplied from a small portable insulation transformer.

[jdragoset]

Likely a saturable core oscillator with the main transformer winding's 5,6,7 providing feedback to the transistor bases.
Frequency may be set by the RC network connected to terminal 5.