820-3435 backlight fuse

Kyle93

Active member
820-3435 with no backlight. Original damage is severe burn where backlight fuse goes. Replaced backlight fuse and have fused soldered directly to pin 4 of Q7706 and wire running to R7006 for PPBUS_G3H however every time the backlight starts to activate the wire just burns and separates.

What else should I try?
 

2informaticos

Administrator
Staff member
You should check if any short persists on the board, BEFORE applying power.
Check w/ and w/o LCD connected.
 

Kyle93

Active member
without wire there is no short w/wo lcd but with new wire ran there is a 0.54 short on F7700 w/o lcd and w lcd 0.38

how do you solve something like this besides just scraping away at affected area more?
 

2informaticos

Administrator
Staff member
Do you mean 0.38-0.54 on diode mode?
That is no short at all.
I expected you will check on pins 3/4 of J8300, not only F7700.
 

Kyle93

Active member
Yes readings on pins 3/4 is .572 but jumper wire still burns each time the backlight starts to activate
 

2informaticos

Administrator
Staff member
Did you check on the jumper wire too?
No short or low value?
Pad 2 of F7700 can be damaged and shorted to second copper layer, which is ground.
If is the case, isolate pad 2 and wire pad1 to pin 4 of Q7706.
Be sure R7788 makes contact too.
Also check no short remains on the board, before apply power; especially Q7706 pins.
 

Kyle93

Active member
With a wire on F7700 going to pin 4 of Q7706 and pad 1 of F770 being isolate (no wire to PPBUS_G3H) there is no short 0.806 on diode mode but still smokes when power is applied with or without lcd.

picture attached of damaged area
 

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2informaticos

Administrator
Staff member
Scratch inside the board in that place.
Make a hole in the surface (first layers), and polish the edge.
 
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