[Duo2400] ON Topic: Inverter Board

[Ben Smith (QM Systems)]

> -----Original Message-----
> From: Duo/2400 List
> [mailto:DuoList at lists.themacintoshguy.com]On Behalf
> Of Robert R. Daniel
> Sent: Thursday, December 12, 2002 3:23 PM
> To: Duo/2400 List
> Subject: [Duo2400] ON Topic: Inverter Board
>
>
> Just curious:  what is the function of the inverter board in Duo
> screen?  I know that inverters convert DC to AC and/or vice versa.
> Why is there an inverter in the screen?  As I understand it, the
> Duo power supply converts AC to DC for charging the battery and
> running the motherboard.  I presume the hard drive also runs
> using DC electricity.  Is the function of the inverter board in the
> display to turn DC back into AC for the Cold Cathode Fluorescent
> backlight bulb?  If that's the case, how does one test for a bad
> inverter board as opposed to a bad CCF?

The inverter board takes a DC input (12V?) and outputs a high voltage
(90-150V AC) to power the backlight, if the bulb is failing then it
will still glow, however it may be quite dim and often pink! However
if the inverter has failed then the bulb will not light at all.
I have found that the DC fuse on the inverter board quite often fails
due to old age, however the switching transistors, the transformer,
and the output capacitor are all common failure points.
Please be careful testing the inverter board, although the current is
quite low (a few ma) it can still be enough to give you quite a bolt,
(powerbooks do not appreciate being convulsively flung across the
room!!) also without a bulb to load it the output can rise to 400V or
so.
Ben.