MPC 3000 backlight going on and off

First of all, thanks so much Misterwhite for the great hints on checking the inverter.
viewtopic.php?f=4&t=172841

My display light is going on and off randomly. The backlight foil I have is the non-solderable one from ebay and is still quite new, so I then suspected the inverter.
I checked the voltage with the meter and is giving me a stable reading of 142V, so I guess that means that the inverter is good! The display contrast switch is also working fine... I also checked the conectors
What else could it be? Any other components (capacitors...) on the filter pcb that should be replaced?
Again, sometimes the screen flashes rapidly and sometimes the light goes to sleep and it comes back on after a while. It's driving me crazy!
Any help would be much appreciated

Carlos

moral97 wrote:First of all, thanks so much Misterwhite for the great hints on checking the inverter.
viewtopic.php?f=4&t=172841

My display light is going on and off randomly. The backlight foil I have is the non-solderable one from ebay and is still quite new, so I then suspected the inverter.
I checked the voltage with the meter and is giving me a stable reading of 142V, so I guess that means that the inverter is good! The display contrast switch is also working fine... I also checked the conectors
What else could it be? Any other components (capacitors...) on the filter pcb that should be replaced?
Again, sometimes the screen flashes rapidly and sometimes the light goes to sleep and it comes back on after a while. It's driving me crazy!
Any help would be much appreciated

Carlos

It sounds like a bad connection somewhere. Make sure that none of the EL foil is exposed touching a part of the LCD circuit causing it to short out.

Since you have already checked the connections for loose/dry solder joints, you may want to measure the output of the inverter as the backlight flickers. The inverter may behave differently when it is under a load.

If the inverter output stays constant, that would indicate an issue with the backlight. If the inverter output is erratic, it could be a an issue with the inverter circuit (bad inverter, leaky capacitors, issue with power supply etc).

Thanks MpcHunter,
During the last days it doesn't flicker anymore, it just stays off all the time.
I will open the screen to see if I find something wrong there as you mention , and take another reading of the inverter output.
Cheers

Carlos

Hi Carlos,

I wonder if you could try these 2 things as well - you don't need to open up the display for this, just open the MPC so that you can see the inverter.

Test for a bad connection in the area of the connector:
- power on your MPC
- make sure the backlight on/off switch (contrast knob) is on (you should hear a high pitched noise coming from the inverter when ithe switch is on, that noise will disappear when the switch is off)
- locate the backlight power cable where it plugs into the inverter/filter PCB
- gently move the power cable from side to side. See if moving the cable causes the backlight to light, even if it only lights for a short time

If moving the cable makes no difference, very rarely there is a situation where the inverter cannot 'start'. This will force the inverter to start working.
- power off your MPC
- unplug the backlight power cable from the inverter/filter PCB (P855)
- power on your MPC
- make sure the backlight on/off switch (contrast knob) is on (you should hear a high pitched noise coming from the inverter when ithe switch is on, that noise will disappear when the switch is off)
- you need to re-connect the backlight power cable, while the backlight power switch is on

Let me know what happens. Of course if there is a problem with the backlight, I will send a replacement. And if it is a problem with the power header at P855, this is not too difficult to fix. It sounds like your inverter is working properly.

Thanks!

MisterWhite, I followed your instructions but the display never went on or flickered.
While I was doing it, the wierd thing is that I couldn't tell when the backlight was on or off because I couldn't detect any noise coming from the inverter when turning the switch on and off.
After that I took out the multimeter and checked the voltage again on the pins of the connector. This time I got NO VOLTAGE! Wierd, because the last time I got a stable reading of 142v.
Does this mean that the inverter was just taking its last breaths (all the flickering and strange behavior) and finally expired? Or, as you mentioned, could be a problem with the power header at P855?
What do you think?
Just in case I had ordered one of the 5 volt inverter for EL-panels from Backlight4you which supposedly work as a replacement ...
Thanks for your support

Carlos