I have a Dell 1905FP which powers up(Power LED on) but the backlight just blinks very shortly, about 0.5sec.
If I disconnect 2 of the wires for the backlight(1 side of the inverter), there is no difference, but if I disconnect the other 2 I don't get that "startup blink"
Is the LCD panel defective or should I start looking at the inverter?
Any input is welcome.
Thanks

/Morten Dalsgaard

The inverter is the most common problem but lamps do fail, the lamps are usually along the top and bottom edges but some are behid the panel.

Rich

Is it possible to change the lamps or do I need a new panel?

Regards
Morten Dalsgaard

It depends on the construction of the panel as to how easy it is to replace the lamps. Some slide out from the sides others need a little dismantling of the panel.

Its best if you can get some known good lamps similar size and diameter and just connect externally to prove the problem before you go to the trouble of changing them.

http://www.lcdpart.com/doc/ccfl.html

Rich

It seems like the lamps are ok, i've just tested the inverter with another lcd panel, and it acts just the same way.
But I have some difficulties finding the fault. I'm guessing the inverter shuts down because it encounters some sort of error(short circuit, disconnected lamp or other) But I can't find the datasheet for the inverter IC. I haven't got a schematic or a service manual for the monitor either.
The inverter IC is a OZ9RRAG, it's a SO-8.
From what I can measure on the PCB it has some sort of feedback on pin 7, can anybody please supply me info on this signal. Also Pin 8 which seems to be for adjusting the backlight, is this active high or low?

Hope someone can help.

regards
Morten Dalsgaard

The IC is manufactured by O2 Micro, you will need to check the oscillation frequency and 1 common problem is that the transformers break down.

The IC is most likely and OZ96**.

http://www.o2micro.com/

Rich

Hi

It seems the same problems come around all the time..

I have four dell 1704FPV monitors which all have similar problems, either a flickering backlight or backlights that turn off after a few minutes/seconds, lowering the brightness increases the time the backlight will stay on but you still get the flickering. My customer told me they had several of these monitors replaced when they first got them due to a design fault with similar symptoms. Three of the monitors also do not work on the D-SUB connector but will on the DVI connector, There are BKLT_EN and BKLT_ADJ signals from the graphics processor (gm5321) board to the inverter so I am not ruling out a related problem.

I have tried to get the schematic from Dell but had no replies to my queries, I know I can get the PSU/inverter board for US$45 each on ebay or lcdrepair in the US but with postage to NZ and the other problem with the VGA socket it is not really going to be cost effective. I have told my daughter I will donate them to her school if I get them working so I am now going to attempt a component level repair.

I have a good electronics background but to date have never dealt with switched mode systems (I had a shock off a switch mode board that had been on a shelf for 2 days so I am very wary of them!)

If anyone has a schematic or has fixed a similar problems I would be grateful for their help. I will post my results here for future readers...

Boz

Hi

Update. I never did get a response from Dell, so you are a bit on your own with these! Things of interest were.

1. The flickering backlight was one of the CCFD tubes not the inverter (spent some time testing caps and coils for breakdown!). the Dell has a dual inverter on the same PCB and each powers two CCFD's (four in total). I was lucky enough to have a spare monitor with a smashed screenand a good working CCFD to replace one of these and get it working.

A replacement of the AUO M170EG01 back lamp is possible with a **lot of care**, if you remove the three screws holding the TFT PCB and cover then carefully prise apart the case, once the layers separate, safely put aside the TFT electronics and the top and bottom back lamp tubes will just pop off the perspex block. I stress again a lot of care needs to be taken as the glass substrate the TFT panel electronics is not protected at the edges and any cracks are terminal!

2. If any one of the back lights fails to ignite then the display switches itself off after a few seconds, again not the inverter and you need to replace the CCFD.

3. I had one remaining monitor and no source of spare CCFD tubes and a dodgy PSU, rather than throw it I decided to make a digital picture frame, basically once the panel was dismantled I squeezed 20 x white LED's in place of the top CCFD each pair of LED's had a 39 ohm reisitor in series to allow 5V operation, the whole PSU board was then thrown away along with the case and a 5V 3A external supply used to power the (gm5321) graphics board, TFT and LED back light. It was much slimmer and lighter and fitted nicely in a wooden picture frame. I wouldn't want to sit in front of it all day as it is not that bright but it works great on the wall and uses far less power and should be uber reliable. (Any new monitor I purchase will definately use LED's, so much easier)

I could not find any info on the gm5321 graphics chip but I assume it is a derivitive of the gm5221, also no information anywhere on the OZ9RRAG either but using any of the OZ9** family as suggested gives a good idea of it's use.

Note for testing without the graphics board I just tied the BKLT_EN to 5V (ON) and the BKLT_ADJ to 0v (0v = bright, 5V = dim).

I also noted a PAL/NTSC composite input is available on the gm5221, it probably needs to be enabled in the firmware (or one of the 200+ pins on the chip!!) as I could not get it to work on the gm5321. if anyone finds how to do this please get in touch!!

Good luck

Boz

www.boznz.com
simple solutions to complex problems

There should be either 4 transistors or 4 mosfets that actually do the push pull operation more than likely 2 are shorted still causing one half of the lamps to light and the PWM chip detects the fault on the other half causing the inverter shut down.