replacing backlight inverter - brightness control

First of all are you certain the inverter is bad? I just fixed a laptop last night that wouldn't light the screen, turns out the enable line to the inverter was stuck low, funny thing is I jumpered it to +5v for a few seconds and then removed the jumper and it's been working fine ever since, guess there was something small shorting it that I managed to burn clear, dunno.

In fact, the lamps light briefly, then the monitor switches off (led goes amber) then it tries again, indefinately...

If the inverter board is disconnected the monitor functions normally - minus a backlight.

The supply to the inverter seems ok, the fuses on the board are okay, nothing looks burned, and I don't have any SMD equipment, so I'm inclined to replace unless anyone can give any specific advice.

Alex

Some of the inverter boards have a ceramic capaciotr across the primary of the output transformer. (about 0.1Uf, I think). I have had a couple of these go bad. The back light would come on then quickly shut down. You might want to check these. I use a NE2 neon bulb , taped to popsicle stick, to test if the inverter is working. The gas in the bulb will glow, if there is high voltage nearby. Hold it next to the output transformers. Hope this helps... John

I don't think it has these. There's a big polyester cap in each channel, and those at the secondary.

See picture:

I disconnected the primary on the right, along with the capacitor and inductor there:

The lamps on the lefthand channel lit up more fully (before the mod) so I thought the other channel might be at fault. I figured the transformer could be at fault, though the transistors could too I can't unsolder them!

The result is the other lamps now stay on for half a second or so, and the monitor doesn't restart. Still not working though.

I think I might have made a logical error: Why would the monitor shut down and restart when the inverter protection tripped? I'm not sure there's a signal there for that purpose. Should I be looking for a power supply problem ?

Many thanks for all your help,

Alex

It's working beautifully now.

The inverter modules, BXA-12579 from JKL*, fitted quite neatly in the space for the old quad module.

They have a more substantial transformer and no surface mount components, so they'll probably outlast the rest of the monitor.

The brightness control seems fine, enough control via the lcd, possibly it didn't vary the backlight level at all. I was thinking of laptop brightness controls, which do.

...Shows the fit. I had to cut a new piece of plastic to separate the HV boards from the screen, I used LDPE from a commercial ice-cream tub.

I imagine there will be a lot more of these dying in the next year or two, could be good business...

Alex

• - actually made by elevam

Nice, there's a lot of space in that thing, I would have guessed it'd be a much tighter fit.

Yeah I'm hoping more of them start dying, greatly increases my chances of picking up a nice dead one for free.