CCFL darkened ends of lamps

[Derek23]

Hi

I have a IBM Thinkvision L170P second hand that works fine (no red tint, and good brightness and even light side to side). I've done a general revision of it (caps, dust, connections) to see if they are in good shape and they are.

However I took out the CCFL lamps of the upper side only (there are 4 lamps in total, 2 in upper side and the other 2 in bottom side).

The right side of both them is darkened while the other one is totally "new".

Does this mean that lamps are too used and they could die "soon"? Does an old lamp both dark its ends? I have another 4 lamps from another monitor (15 inch) that have the same sign and also worked fine (the video circuitry of that monitor just died)

Many thanks.

[Solder Boy]

It's normal for CCFL lamps to have some sort of darkness at the ends. It's no different than a regular flourescent lamp you have in the house. If it's a pale light grey colour I wouldn't worry about it. If it's really really black then time to replace it.

[Derek23]

Hi, many thanks for you reply:

Yes, the color is a sort of dark gray with irregularities, at least compared with the "new" end of the lamp


Here's the photo (sorry for the quality it's taken from webcam, appears more darker than it really is) The upper lamp is showing the clearer end, while the bottom one is showing the darkened one

Many thanks

[Th3_uN1Qu3]

It's alright. You will be able to use the lamps for a couple more years.

[Derek23]

Many thanks the unique I hope so

One question, Lowering the brightness shortens or lengthens the lifetime of CCFL? I have read mixed opinions on the net and I am truly confused

Also I would like to disconnect 2 lamps of the monitor because it is too bright for my eyes even with the minimum brightness (reducing the brightness in Catalyst makes the image look poor here) and my eyes are a bit tired (they are very sensitive), but when I do so the monitor does the "2 seconds to black" (the backlight shuts off) could I trick the inverter to think there are the 4 lamps connected?

Many thanks to all

[alexanna]

Originally Posted by Derek23

Many thanks the unique I hope so

could I trick the inverter to think there are the 4 lamps connected?

Many thanks to all

The 2 second to black you get with lamp[s] unplugged is a safety feature of the monitor.
Leave it alone.

[Derek23]

OK no problem then! I found that there are 3 pots, one near the upper CCFL sockets and the other 2 near the inverter main IC (here the inverter and PSU are fused in one PCB) Can anyone know if I could reduce the brightness further with those potentiometers? I don't want to touch anything for the moment without knowing.
Many thanks!


And now I don't know that the heck I have done that now the backlight is flickering intermittently (specially when I tap the monitor) I will take it apart again and check the connections.
EDIT: solved, the upper CCFLs plugs were loose.

[Krankshaft]

The blackened ends of the tube is the emmissive substance sputtering off the electrodes each time the lamp is started.

This is also a normal occurrence on ordinary hot cathode fluorescent lamps.

Nothing to worry about.

[Derek23]

Originally Posted by Krankshaft

The blackened ends of the tube is the emmissive substance sputtering off the electrodes each time the lamp is started.

This is also a normal occurrence on ordinary hot cathode fluorescent lamps.

Nothing to worry about.

Many thanks, then turning on and off the monitor frequently shortens the lifespan of the lamps? I have WIndows set to turn it after 15 minutes..


Thanks again

[Th3_uN1Qu3]

It doesn't affect their lifetime to any significant degree... Leaving the monitor on all the time isn't the best idea either, because the lamps run a bit warm, and heat is the enemy of all electronics.

[Krankshaft]

That would be true of hot cathode florescent lamps since they contain filaments and the inrush current each time you turn them on will shorten the filaments and therefore the bulbs life. Similar to an incandescent lamp.

But CCFLs have electrodes and no filament to wear. The failure mode of a CCFL is lumen degradation over time due to use rather than outright failure. They can sometimes die unexpectedly but that's usually due to manufacturing defects.

So turn the monitor off when not using it or configure Windows to put it into sleep mode after a certain period of inactivity.

[Derek23]

Originally Posted by Th3_uN1Qu3

It doesn't affect their lifetime to any significant degree... Leaving the monitor on all the time isn't the best idea either, because the lamps run a bit warm, and heat is the enemy of all electronics.

Many thanks, I'll leave it 15 mins before shutting down then though I don't like to leave it on even if I leave for 5 minutes

Originally Posted by Krankshaft

That would be true of hot cathode florescent lamps since they contain filaments and the inrush current each time you turn them on will shorten the filaments and therefore the bulbs life. Similar to an incandescent lamp.

But CCFLs have electrodes and no filament to wear. The failure mode of a CCFL is lumen degradation over time due to use rather than outright failure. They can sometimes die unexpectedly but that's usually due to manufacturing defects.

So turn the monitor off when not using it or configure Windows to put it into sleep mode after a certain period of inactivity.

Many thanks for your elaborated explanation, that is what is called sputtering when I read about the failure modes of CCFL, right?, I configured to shut it down in 15 Minutes (or I turn it off manually)

---------------------------------------------

Meanwhile I've managed to dim it more thanks to the potentiometers on the inverter, there are one that seems to set the voltage/current to the lamps and other two that seems to configure the PWM (speed?), and therefore dim them, though if I dim too much:

• The screen becomes pinkish/reddish
• The screen flickers
• or the inverter shuts down after a while

So I dimmed a bit until the screen doesn't hurt my eyes in the night while maintaining a good working condition of the monitor.

Could this cause damage to inverter or lamps? The monitor seems to be colder than before anyway.

Many thanks

[Th3_uN1Qu3]

Originally Posted by Derek23

Meanwhile I've managed to dim it more thanks to the potentiometers on the inverter, there are one that seems to set the voltage/current to the lamps and other two that seems to configure the PWM (speed?), and therefore dim them, though if I dim too much:

• The screen becomes pinkish/reddish
• The screen flickers
• or the inverter shuts down after a while

So I dimmed a bit until the screen doesn't hurt my eyes in the night while maintaining a good working condition of the monitor.

You found pots? That's a very, very rare monitor you have there... It is normal for the CCFLs to flicker or go pink if the drive current isn't enough. As a matter of fact, that's why i sold one of the monitors i fixed - a 19" NEC which looked superb from all points of view (especially with all the work i did to clean it on the inside and seal it - it was full of dust specks at the bottom when i got it), but at zero brightness the lamps would flicker slightly. I didn't want to take any chances even though it would have probably lasted at least 2 more years... so i sold it.

[Derek23]

Originally Posted by Th3_uN1Qu3

You found pots? That's a very, very rare monitor you have there... It is normal for the CCFLs to flicker or go pink if the drive current isn't enough. As a matter of fact, that's why i sold one of the monitors i fixed - a 19" NEC which looked superb from all points of view (especially with all the work i did to clean it on the inside and seal it - it was full of dust specks at the bottom when i got it), but at zero brightness the lamps would flicker slightly. I didn't want to take any chances even though it would have probably lasted at least 2 more years... so i sold it.

Hi!
The monitor is a IBM Thinkvision L170P
Yeah there are 4 pots that were a bit glued but were easy to move, inside of the PSU-inverter board. I adjust them while the monitor is ON (a bit risky lol)
There is 1 near the PSU output connector (I haven't touched this one, maybe adjust the PSU voltage output (?) )

Another one near the upper CCFL connectors that seems to adjust the CCFL voltage and/or current applied to these because it dims/brightens the screen further the normal brighness control can, and dimming too much makes the symptoms above described.

and another 2 near the main inverter IC, which one seems to adjust the PWM duty cycle and therefore the brightness (because the sound coming from transformers changes its pitch) and the other one doesn't seem to make any difference (maybe the CCFL strike voltage?)

I will try to make a photo but I don't have a proper digital camera, I'll try with the laptop webcam LOL.


BTW it also flickers a bit randomly when the brightness is set to 0 and disappears if set to 2 or higher, even before I touched the pots! the inverter seems to change pitch when happens.

Thanks