White screen repairs

[harp]

To ask here... I have few devices with white screen problem, actualy nokia 2220 and some fuji? camera, and try to understand what is common problem to cause that issue.
Yes, both devices work everything else probably ok, I mean, I hear intro melody and keypress click sound, DTMF tone, power on off... all ok.
On desk is nokia 2220 slide, and I check all screen connectors and components arround it, measure voltage drop, but all looks ok. I suspect on slide flex cable, but it look ok and white screen is not interupt while flexing board, pushing conectors, and sliding up down. In attachment pin 10. is typo must be 0.028 to ground.

On camera (I dont have it at the moment) I remember there is also white screen input from CCD, but on screen is present system icons for setting and can walk through it. If I make picture or video, it maike it, but white...

I like to learn how to troubleshoot causes of obiously missing some signals on screen connector, because background power is working ok.
Second, if I connect all conector in place, it cover all area arround it and cant picking anymore on pins. How to aproach to this problem without bunch narrow cable extendors?

[harp]

I have measure VDD pin #19 is 6.64v stable and corespond to backlight behaveour.
Pin #11 is stable 1.78v (VOUT)

On RESX pin #14 I noticed to periodicaly grounded activity.
Pin #15 (CSX), #16 (SCL), #17 (SDA) have short activity (say 0.3 sec) over regular interval of every 3 seconds about... I dont know if it is normal or not?

Some guide, hint, tips will help a lot The board become war field... I jumpered everithing with wires to do listed measurement.

[mon2]

Be sure you are not measuring in diode mode or in resistance mode with power to the board.

Test the lines again but in diode mode. Red meter probe (yes red) to ground and black meter probe to the point to test. Post each diode mode measurement. No power to the board in diode mode testing.

[harp]

Yes, that measurement (diode mode, red on ground, no power) are listed in first post attachment, it is motherboard connector to screen. Pin #10 is typo, must be 0.028v
For me, all looks good?

[mon2]

Pin # 10 is very low for a DIODE mode reading. This looks like it is defective. Review the condition of the component @ N2400 in the schematic. What are the topside markings? This looks like a switching regulator.

[harp]

I checked again, pin #10 (with voltcraft 91 dmm) is 0.028v in both direction, it is FB pin that is grounded to ground through 27R (R2402), but, when powering up, VOUT on pin #11 is steady 1.78v, so look like ic and FB is working ok?
I check also resistance to ground pin #10 is 27.4 ohm, so if the paralel resistance of faulty ic is significient, there be some lower reading.

The whole board is taped and wraped with lots of jumper wires and kapton tape, like franckenstein type, so it is not handy right now to look under shield. You think that is some power issue cause white screen?
I look before, and nothing have burnmark or liquid damage, look fine, but not look for ic label.

[mon2]

I think your conclusion is correct. The 27R2 resistor is causing this false reading in diode mode. Good thing you confirm with the resistance mode. This must be a 1v8 buck regulator which is working ok.

Just now, fixed a Yamaha keyboard that had a 'white LCD display issue'. Fixed with low heat + flux applied onto the LCD fpc cables that are soldered. Not sure if your case will be the same but the replacement B&W LCD is only available from China for this keyboard @ ~ $ 100 USD + shipping. Found a YT video on this topic. Have you searched out YT for your fault? Perhaps the same? Old LCDs with dry solder connections. Need to keep the heat low so that the LCD does not burn out. I can post pix of this Yamaha keyboard repair after a late lunch. The local music store is sending us instruments to repair as there is no one else in the city who handles board level service.

[harp]

I was managed to resolder all 3 of 4 FPC-24 connectors with soldering iron... I designed a special soldering tip just for that, hence whole connector is 4.5mm in size.

One male connector I skip to touch because it is way to risky to mess arround, it is all exposed so tin easely can soak in it. It is simmilar like attached pic. But look ok.

So, when all was assembled, I got exactly the same white screen again
Any help will welcome.

I dont know, is signals must pulsate every 3 sec, like I mentioned before, normal?