LCD backlight problem
 

I have a dell 1504FP (LCD monitor). The backlight doesnt work for a period
of time.

On close examination with a scope on the PSU board, BIT3105 (lamp controller
IC) is getting confused. It has several pins to do with OLP (open lamp
indicator)- basically the chip switches itself off if it thinks one of the
lamps is open circuit. The lamps are definitely all working. I can recreate
the problem by disconnecting any one lamp.

The OLP circuit waits for a cap to reach 2.5v before monitoring- if I drain
that cap, the monitor works.

Could someone look at the BIT3105 data sheet and tell me how to disable the
OLP circuitry- I dont care if it shortens my monitor life. Please help.

Thanks in advance.

Michael.

LCD backlight problem
 

"Michael" wrote in message
ng.com...
I have a dell 1504FP (LCD monitor). The backlight doesnt work for a period
of time.

On close examination with a scope on the PSU board, BIT3105 (lamp
controller
IC) is getting confused. It has several pins to do with OLP (open lamp
indicator)- basically the chip switches itself off if it thinks one of the
lamps is open circuit. The lamps are definitely all working. I can
recreate
the problem by disconnecting any one lamp.

The OLP circuit waits for a cap to reach 2.5v before monitoring- if I
drain
that cap, the monitor works.

Could someone look at the BIT3105 data sheet and tell me how to disable
the
OLP circuitry- I dont care if it shortens my monitor life. Please help.

Thanks in advance.

Michael.



Perhaps a resistor across that capacitor would make it less sensitive? How
are you draining it? Just shorting across it?

LCD backlight problem
 

The capacitor is on pin 19 of the chip. Its the soft start for the lamps.
For normal function, I think the cap has to fully charge (goes to around 9v
i think), but the OLP circuit doesnt cut in till 2.5v. I dont really want to
tinker permanently with that cap.

Anyone know where I can get a BIT3105 (in the UK), I might change it out in
case its faulty.

Michael.

"James Sweet" wrote in message
news:Y403f.31290$A52.27045@trnddc02...

"Michael" wrote in message
ng.com...
I have a dell 1504FP (LCD monitor). The backlight doesnt work for a
period
of time.

On close examination with a scope on the PSU board, BIT3105 (lamp
controller
IC) is getting confused. It has several pins to do with OLP (open lamp
indicator)- basically the chip switches itself off if it thinks one of
the
lamps is open circuit. The lamps are definitely all working. I can
recreate
the problem by disconnecting any one lamp.

The OLP circuit waits for a cap to reach 2.5v before monitoring- if I
drain
that cap, the monitor works.

Could someone look at the BIT3105 data sheet and tell me how to disable
the
OLP circuitry- I dont care if it shortens my monitor life. Please help.

Thanks in advance.

Michael.



Perhaps a resistor across that capacitor would make it less sensitive? How
are you draining it? Just shorting across it?

LCD backlight problem
 

Sorted it! I soldered a 47k surface mount resistor over the surface mount
capacitor (C25, on underside of PCD, near BIT3105- in case anyone has this
problem in the future) and it works fine. OLP circuit disabled. I think I'll
notice if any of the lamps die- dont need all that overengineered circuitry.
Thanks for your help people.

Michael.

"Michael" wrote in message
g.com...
The capacitor is on pin 19 of the chip. Its the soft start for the lamps.
For normal function, I think the cap has to fully charge (goes to around
9v i think), but the OLP circuit doesnt cut in till 2.5v. I dont really
want to tinker permanently with that cap.

Anyone know where I can get a BIT3105 (in the UK), I might change it out
in case its faulty.

Michael.

"James Sweet" wrote in message
news:Y403f.31290$A52.27045@trnddc02...

"Michael" wrote in message
ng.com...
I have a dell 1504FP (LCD monitor). The backlight doesnt work for a
period
of time.

On close examination with a scope on the PSU board, BIT3105 (lamp
controller
IC) is getting confused. It has several pins to do with OLP (open lamp
indicator)- basically the chip switches itself off if it thinks one of
the
lamps is open circuit. The lamps are definitely all working. I can
recreate
the problem by disconnecting any one lamp.

The OLP circuit waits for a cap to reach 2.5v before monitoring- if I
drain
that cap, the monitor works.

Could someone look at the BIT3105 data sheet and tell me how to disable
the
OLP circuitry- I dont care if it shortens my monitor life. Please help.

Thanks in advance.

Michael.



Perhaps a resistor across that capacitor would make it less sensitive?
How
are you draining it? Just shorting across it?