3 pin scanner inverter

[klayus]

Can anyone help me? I've taken apart a konica copier machine and i salvaged among other things this lamp with its inverter.
the problem is the inverter has 3 pins on the input. by following the traces to the capacitor i've found which one is the + and the ground but i cant figure out whats the 3rd (middle) pin and the lamp dosen't start! it dosent draw any current either.
i gave it 15V on the + and middle pin, i even put the middle pin to ground, but nothing happens.
i didnt try giving it the full 24V as all of my other scanner light inverters start with less than their full voltage.
here are some pics:


please help

thanks in advance

[Paul Price]

Check F1, the fuse.

[klayus]

I bypassed it and it still dosent turn on

[Paul Price]

Did you retry grounding or pulling up the center lead again?

Was the scanner lighting up before you took it apart, showing the inverter was ok?

Try to find a specsheet for the IC.

I can see the inverter IC abd it just doesn't look like it requires a special signal on the middle connector pin, there are not enough pins on this chip or the power connector. There are usually other pins used for clock/data/enable functions.

Some scanner inverter chips do use a serial bit stream to send control  commands to set brightness/on/off. .just a hunch this is the case, the specsheet tells the full story. I cannot make out the IC Mfg. part # to check this, it is up to you.

The most common failures of these inverters is HV arc-over that destroys the inverter transformer and this due to failure of the lamp it is connected to.

I cannot see on the bottom of the PCB any connection from the connector center wire to any other part of the circuit. The pin's trace seems to end near the fuse.

[klayus]

The middle pîn goes to a leg of a transistor but I can't figure out what happens after it. The ic is a 10393 comparator so i'm guessing there should be some voltage on that pin to maybe set the intensity of the light. I'll try with a pot and see where that takes me.
I'm pretty sure it was working as I have another one with a similar inverter, 3 pins, and I can't start that one either. That one has a pc494 inverter controller on it.

Any other opinion is greatly appreciated.

L.E. i tried with a pot the wiper feeding the middle pin and nothing happened. i'll try with pwm on that pin see where that takes me.

[klayus]

I got it working! The middle pin has to be put to ground through a current limiting resistor after the circuit starts.
[Img]http://i62.tinypic.com/1448ozl.jpg[\img]
thanx for your help
best regards