Yes back in theday, I had a unit that had obviously been retro fitted in our
old commer, and when it went on the blink, at first I had no idea of how it
worked.
In the end I sussed that it basically had three main bits. A Unijunction
transistor as a high frequency oscillator f driving two power transistors
with the high voltage generated by a centre tapped transformer, then the
output rectified. The third part appeared to be some kind of current sensor
that operated a regulator for the heaters for a second or so until the tube
started to take current. I rmremember this one as it was one of the few
where the transformer was not to blame, it was one of the two output
transistors that had gone open circuit internally.
I suspect these days its all done in one chip and therefore nobody can fix
them.
Get a decent meter though, as cheapo ones have poor protection.
Brian

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From the Sofa of Brian Gaff Reply address is active
"Bill" wrote in message
...
In message , "Dave Plowman (News)"
writes
In article ,
David wrote:
I am trying to fault find a fluorescent light on the 12V circuit in our
motor home.

Opinion seems mixed, but there are several postings which claim that
these are actually 240v AC lights with a built in inverter so that they
can run off 12V.

There is certainly a lot of circuitry inside.

Firstly, do camper/caravan/boat 12V fluorescents usually run at 240V
with a built in inverter (or sometimes)?

Secondly if so is there usually clear marking of the 12V and 240V parts?

I don't particularly want to probe a 240V AC circuit with the 50V DC
part of my little multi-meter.

There are probably lots of ways of doing it but the most simple is
basically just an oscillator and transformer to produced approx 240v AC.
Plus a way of producing a higher voltage pulse for starting.

A thought about replacement, with a bit of mechanical ingenuity, an
emergency light unit would provide the parts to make a good replacement.
Probably a darn site cheaper than a new fitting from a motor home shop.


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Bill