Backlight Dummy Load???
 

I pick up free lcd monitors at garage sales and fix 'em.
Biggest problem is getting them to run while you have 'em
disassembled.
Seems as if they TRY to make it hard to run 'em.

Would be much easier if I didn't have to hook up the backlights.
But running the inverter with out a load is surely a BIG STRESS
on the transformers and maybe the driver.

What's a good dummy load that I can put on the connections to keep
the voltage spikes from arcing/shorting the transformer secondary?
The lamp load is decidedly nonlinear. And there's several watts to
dissipate.

Cutting the power supply trace to the inverter works, as long as the
problem isn't in the inverter supply, but it's
kinda brute force.

I have a bunch of laptop backlights, but I'm afraid to use them
as load for bigger monitors. Big current difference.

Anybody successfully constructed a backlight proxy (dummy load)?
Explanation?

Thanks, mike

Backlight Dummy Load???
 

On Aug 22, 9:42*am, mike wrote:
I pick up free lcd monitors at garage sales and fix 'em.
Biggest problem is getting them to run while you have 'em
disassembled.

Would be much easier if I didn't have to hook up the backlights.
But running the inverter with out a load is surely a BIG STRESS
on the transformers and maybe the driver.

I have a bunch of laptop backlights, but I'm afraid to use them
as load for bigger monitors. *Big current difference.

I've just put a cheapo, relatively large lamp on a scavenged
connector (with lots of insulation, of course; there's kilovolts
there).
JKL made a bunch of inverters available standalone, and a few
lamps, and there were only a few HV connector types we
had to deal with, so it was possible to test lamps with known-good
inverters, and inverters with known-good lamps.

Backlight Dummy Load???
 

On Sun, 22 Aug 2010 09:42:28 -0700, mike wrote:

I pick up free lcd monitors at garage sales and fix 'em.
Biggest problem is getting them to run while you have 'em
disassembled.
Seems as if they TRY to make it hard to run 'em.

Would be much easier if I didn't have to hook up the backlights.
But running the inverter with out a load is surely a BIG STRESS
on the transformers and maybe the driver.

What's a good dummy load that I can put on the connections to keep
the voltage spikes from arcing/shorting the transformer secondary?
The lamp load is decidedly nonlinear. And there's several watts to
dissipate.

Cutting the power supply trace to the inverter works, as long as the
problem isn't in the inverter supply, but it's
kinda brute force.

Some turn off if the backlight not running, too. Backlight CCFL is run
on constant current (there's a little rectifier/smoother in the HV return
lead), so perhaps a smallish value power resistor in series with a 400V
or so TVS diode (bidirectional or two unis in inverse series) would be
a nice load? Say 470R to 2k2 HV resistor + TVS?

I have a bunch of laptop backlights, but I'm afraid to use them
as load for bigger monitors. Big current difference.

Given that the HV is current regulated, maybe they run at similar
currents? Longer tubes would have higher voltage? Tube diameter
seems the same (tiny! 3mm?) on the few I've come across. I see
two in parallel on larger screens rather than one CCFL with a
larger diameter.

Anybody successfully constructed a backlight proxy (dummy load)?
Explanation?

Not tried it (yet), but what I wrote above seems logical start point,
try it on what spares you have now?

Depends on what the fault is, for how far I'm willing to dismantle
an LCD, usually obviously stressed power supply caps, or blown CCFL
inverter needing replacement tank cap (thanks to Internet goodness
for that fix :) I've been able to connect CCFLs and all for testing
before reassembly. Haven't felt the need yet for dummy CCFL.

My repair success rate is 5 1/2 of 7.

The half working one is usable but has odd shimmering pixel effect
in one corner no one here could help with at the time. Here's the
web page in case somebody has seen the effect, but missed my first
post: http://grrr.id.au/odd-lcd/ I didn't dismantle further because
the LCD is usable as it is, hasn't got worse over last few months.
I'd have another try if I received some positive information, or get
another screen so it matters less if I bust this one on further
dismantling. I'm wary of breaking the film to glass connections by
taking the metal frame off. My working space is a little cramped.

Grant.

Backlight Dummy Load???
 

mike wrote:
I pick up free lcd monitors at garage sales and fix 'em.
Biggest problem is getting them to run while you have 'em
disassembled.
Seems as if they TRY to make it hard to run 'em.

Would be much easier if I didn't have to hook up the backlights.
But running the inverter with out a load is surely a BIG STRESS
on the transformers and maybe the driver.

What's a good dummy load that I can put on the connections to keep
the voltage spikes from arcing/shorting the transformer secondary?
The lamp load is decidedly nonlinear. And there's several watts to
dissipate.

Cutting the power supply trace to the inverter works, as long as the
problem isn't in the inverter supply, but it's
kinda brute force.

I have a bunch of laptop backlights, but I'm afraid to use them
as load for bigger monitors. Big current difference.

Anybody successfully constructed a backlight proxy (dummy load)?
Explanation?

Thanks, mike
Why not borrow two tubes from a broken screen, mount them in a box,
and use them as ballast?

Backlight Dummy Load???
 

On Mon, 23 Aug 2010 00:26:57 +0200, Sjouke Burry wrote:

mike wrote:
I pick up free lcd monitors at garage sales and fix 'em.
Biggest problem is getting them to run while you have 'em
disassembled.
Seems as if they TRY to make it hard to run 'em.

Would be much easier if I didn't have to hook up the backlights.
But running the inverter with out a load is surely a BIG STRESS
on the transformers and maybe the driver.

What's a good dummy load that I can put on the connections to keep
the voltage spikes from arcing/shorting the transformer secondary?
The lamp load is decidedly nonlinear. And there's several watts to
dissipate.

Cutting the power supply trace to the inverter works, as long as the
problem isn't in the inverter supply, but it's
kinda brute force.

I have a bunch of laptop backlights, but I'm afraid to use them
as load for bigger monitors. Big current difference.

Anybody successfully constructed a backlight proxy (dummy load)?
Explanation?

Thanks, mike
Why not borrow two tubes from a broken screen, mount them in a box,
and use them as ballast?

Make a small lightbox for checking PCB prints, useful too ;)

Grant.