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820-00165 No backlight, Im stumped.

S

StraightToThePoint

Member
Im getting a short every time I plug in the screen, my first suspect was Q7707, however I have already replaced it and everything measures correctly. EDP_BKLT_EN is 3.2V, same with BKLT_PLT_RST, its at 3.2V as well.

When I plug in the screen LCDBKLT_EN_L gets 0V, and Q7706 gets shorted somehow. PPVIN_S0SW_LCDBKLTFET goes to 1V, on F7700, and on Q7706 (Pin 4) and R7788, R7789, and C7782.

By the way PPBUS_G3H is at 8.6V, but goes to 1V on PPVIN_S0SW_LCDBKLTFET

When the screen is unplugged I get 8.6V on F7700, and 8.6V on PPVIN_S0SW_LCDBKLTFET. Q7706 does not open of course but then there is 8V on LCDBKLT_EN_L.

Resistance of R7788 and R7789 are correct

I have already replaced C7782, Q7706 (Twice) and Q7707.
 
2informaticos

2informaticos

Administrator
Staff member
Did you check diode mode at K/D7701 w/ and w/o LCD connected?

"By the way PPBUS_G3H is at 8.6V, but goes to 1V on PPVIN_S0SW_LCDBKLTFET"
Bad F7700.
How can you think a good fuse has different voltage on its pins?

"When the screen is unplugged...."
What you expect to get then?
Any voltage measured is nonsense in such case.
 
S

StraightToThePoint

Member
F7700 turns to 8V (G3H and PPVIN_S0SW_LCDBKLTFET) when screen is unplugged. Its a changed fuse as well, and is not blown.

D7701 diode mode measures (red probe at ground) measures 0.520V (without screen plugged in and with screen plugged in)
 
2informaticos

2informaticos

Administrator
Staff member
Do you have same voltage on both pins of F7700, w/ and w/o LCD connected???

"D7701 diode mode..."
Which pin???
I was asking about its cathode...
 
S

StraightToThePoint

Member
It was the fuse! You were right! It was trolling me, I normally measure if fuses are good or bad with resistance, however when i checked continuity through it, no beep, so thank you!

However another thing is wrong, I get backlight however on only half of the screen, tested on 2 good screens and both have the same issue. R7720 - R7722 both measure 0V when should be 14V correct? This has to be U7701 correct?
 
2informaticos

2informaticos

Administrator
Staff member
"should be 14V"
Why do you suppose that???

Check if all return resistors are good and post diode mode to ground on them.
 
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