Bypass defective lamp?

[lucky13]

OK, I've seen my share of LCD monitors where only one of the lamp is gone.

Typically , the 4 lamp ones would have 2 lamps on top and 2 lamps on the bottom.

So, if only one of the 4 is gone, the inverter still shuts off the lamps to prevent damage to the inverter board's transformers (from what I've read).

There is over voltage protection and current sensing circuitry all built around the inverter IC.

I have sub in a good lamp for the bad lamp outside of the LCD panel and found the brightness is not significantly reduced. heck, even subbed out 2 lamps still make the monitor quite usable.

So my question is this. Is there a "simple" way to defeat the drive for one lamp or one set (i.e., 2 lamps) on the inverter board so it does not think there is bad lamp and shuts off all the light?

This way, I can rig up quite a few monitors as usable instead of going to recycling.

[PlainBill]

Re: Bypass defective lamp?

OK, I've seen my share of LCD monitors where only one of the lamp is gone.

Typically , the 4 lamp ones would have 2 lamps on top and 2 lamps on the bottom.

So, if only one of the 4 is gone, the inverter still shuts off the lamps to prevent damage to the inverter board's transformers (from what I've read).

There is over voltage protection and current sensing circuitry all built around the inverter IC.

I have sub in a good lamp for the bad lamp outside of the LCD panel and found the brightness is not significantly reduced. heck, even subbed out 2 lamps still make the monitor quite usable.

So my question is this. Is there a "simple" way to defeat the drive for one lamp or one set (i.e., 2 lamps) on the inverter board so it does not think there is bad lamp and shuts off all the light?

This way, I can rig up quite a few monitors as usable instead of going to recycling.

Simple, good, or right?

The simple way is to substitute an appropriate resistor for the defective lamp. At a guess, try something around 150K ohm, 5 watt.

A good way would be to analyze the monitoring circuit and substitute the proper value resistors so it doesn't fail.

The right way is to replace the bad CCFL.

PlainBill

[Krankshaft]

Re: Bypass defective lamp?

Honestly though CCFLs aren't like UHP arc lamps in projectors that cost $250 bucks or more they are dirt cheap.

Now for testing purposes to see if it's a bad CCFL I'm all for it.

[PlainBill]

Re: Bypass defective lamp?

Honestly though CCFLs aren't like UHP arc lamps in projectors that cost $250 bucks or more they are dirt cheap.

Now for testing purposes to see if it's a bad CCFL I'm all for it.

There is one consideration - dexterity. I've known guys who could break anything they try to repair. Anyone with similar dexterity should NOT try to replace a CCFL.

PlainBill

[Krankshaft]

Re: Bypass defective lamp?

If you can't remove and install a 2 terminal SMD component without tearing up traces then this isn't for you.

I think the dexterity part is in that ballpark .

[lucky13]

Re: Bypass defective lamp?

If you can't remove and install a 2 terminal SMD component without tearing up traces then this isn't for you.

I think the dexterity part is in that ballpark .

Hmm.. the lamp?

I took one apart before to remove the lamp. The metal bracket no longer snaps tight. Needless to say, that was junked....

Replacing the lamp isn't a big deal. Just the process of extracting it out of the lcd module and installing a good lamp back in. They don't screw together. They all have these metal points that snap tight!

Hence my idea of just bypass the bad lamp.

[PlainBill]

Re: Bypass defective lamp?

Hmm.. the lamp?

I took one apart before to remove the lamp. The metal bracket no longer snaps tight. Needless to say, that was junked....

Replacing the lamp isn't a big deal. Just the process of extracting it out of the lcd module and installing a good lamp back in. They don't screw together. They all have these metal points that snap tight!

Hence my idea of just bypass the bad lamp.

Yes, I understand. But it was a bad idea. With care an LCD panel can be disassembled and reassembled.

PlainBill

[Demix]

Re: Bypass defective lamp?

Yeah, i destroyed two screens today because I was being careless and its a mistake i will have learnt from, an expensive mistake though ¬_¬ one screen i took apart to swap over a CCFL to the other and i broke the ribons that were attatched. The other screen, the front slipped and yanked off the bit where the graphics boards wire is attatched. I know its not a very good example but yeah :P it isnt too hard aslong as you have the time and skill and your not in a clumbsy mood lol.

[lucky13]

Re: Bypass defective lamp?

Yes, I understand. But it was a bad idea. With care an LCD panel can be disassembled and reassembled.

PlainBill

And proper tools too! And extra hands....

[PlainBill]

Re: Bypass defective lamp?

And proper tools too! And extra hands....

The most involved I have found is the panel found in the Viewsonic VP211b. There are a lot of screws, brackets, etc to remove just to get down to the bare panel. At that point 'special' tools are needed. You need a flat tip screwdriver with a blade at least 3/8" wide. You need a '00' or '000' Philips screwdriver. And you need about a dozen round toothpicks (to keep the frame wedged away from the catches).

PlainBill

[EGuevarae]

Re: Bypass defective lamp?

The most involved I have found is the panel found in the Viewsonic VP211b. There are a lot of screws, brackets, etc to remove just to get down to the bare panel. At that point 'special' tools are needed. You need a flat tip screwdriver with a blade at least 3/8" wide. You need a '00' or '000' Philips screwdriver. And you need about a dozen round toothpicks (to keep the frame wedged away from the catches).

PlainBill

I agree. That VP panels are a pain to disassemble/reassemble.
You need to be VERY careful to do this kind of stuff

[lucky13]

Re: Bypass defective lamp?

And you need about a dozen round toothpicks (to keep the frame wedged away from the catches).

PlainBill

Thanks for the tip!! I will try that next time.