Casio FZ sampler - EL backlight problem

[Peacefrog]

I am repairing a power board in a Casio FZ-20M sampler - and while I've got the 5V, 12V, and 15V rails up and working the EL backlight doesn't seem to be doing what I'd expect.

The schematic is attached - the circuit is powered by the 5V rail, and I'd expect it to be putting out 90V AC - but it actually measures 140Hz 9V AC without a load. I've tested the caps, resistors, and transistors and all seems in range.

I wonder if I'm missing something, as I'm not too familiar with how the circuit works - could anyone help me diagnose? In particular, I'm wondering if this needs a load in order to work correctly. Thanks!

[RoGeorge]

In the collector of the 2SD400F should be stable DC voltage.  If yes, check all 5 components between B, E and pin 7 of the transformer, including the transistor.  Together they make an oscillator.  The worst would be to have short-circuit turns in the transformer, but let's hope not.  I would check or replace the 5 components first.

[fzabkar]

I would test the transformer out-of-circuit. Apply a sinusoidal input between pins 2 & 3 and measure the output between pins 2 & 5. (Of course, do the easy stuff first.)

[Peacefrog]

I was able to find a spare scrap board with the same inverter, and it's fired right up after transplanting in the transformer.

The one problem - *without* load (which I understand is not advisable, so I haven't been leaving it powered this way long), I measure ~240V AC and 1.4kHz - am I safe to connect the backlight, in the belief that this will drop? I'd expect it more in the ~120V AC / 160Hz(?) range.