(347) 552-2258 help@rossmanngroup.com

[SOLVED]820-4924 no backlight

Status
Not open for further replies.
A

Allstartek

Member
Yes I'm pretty new at this. No I haven't found an article for this specific issue:)

I tried this first with the board out and no LCD connected.. I assume this is the wrong way to test circuits so I connected the LCD panel.

Here is what I found and can you please assist me in sorting this out? one odd thing I found is that as I tested some pins on some Resistors etc. The voltage was slowly decreasing.

Thank you in advance,
Chris

U7700 pin 17 en 3.3v
F7700 12.58v

PPVIN_S0w_LCDBKLT_R pin 1 c7700 12.58V pin 2 12.78V
R7701 pin 1 12.59v Pin 2 12.48V

Q7700
Pin 1 10.2v and decreasing
Pin2 8.36 and decreasing
Pin3 12.49v
Pin4 12.59v
Pin5 7.62 decreasing
Pin67.02 decreasing

L7710 PIN 1 8.2V and decreasing PIN 2 8.1V Decreasing

PPVOUT_S0_LCDBKLT
J8300 Pin 1 12.5V
 
A

aprendiz

Moderator
Voltage on Pin 30??? If you use a flashlight , can you see any image???? have you tried whit a known good display assembly??
 
A

Allstartek

Member
Cant believe I missed this reply.. been waiting.. Damn.

Yes the LCD is good. Can see the Apple Logo etc. HDMI port works also.
 
A

Allstartek

Member
I had the original LCD and had a an image but no backlight. Now, With the board out of the case but plugged into the LCD I cant even see an image..
Pin 30 has 5.1V
 
A

Allstartek

Member
I put the board back into the case and I have a no backlight scenario. There is video, just no backlight. with 5.1V at pin 30
 
D

dukefawks

Administrator
With 5V on pin 30 there should be something on the LCD. What voltage is on pin 1? Only 2015 LCD assemblies will work on these boards, make sure you have the correct one.
 
A

Allstartek

Member
no obvious corrosion. I see a very little bit at these 3 resistors
R7731 12.5v on pin 1 nothing on pin 2.. no voltage on either side of R7732..
R7731 Nothing..
R7732 150k Ohms

Looks like R7731 is bad
 
S

SMMRepair

Member
That's only a 3% difference; if it's the same package, and will fit without issues, it should be fine as long as the original spec tolerance is 5%.
 
A

Allstartek

Member
Damn... yea well without ordering 100 of them it's a challenge.. I wish Lewis sold a kit with the top 20 components..
ill just keep searching. Thank you for your help.
 
larossmann

larossmann

Administrator
Staff member
Allstartek said:
Damn... yea well without ordering 100 of them it's a challenge.. I wish Lewis sold a kit with the top 20 components..
ill just keep searching. Thank you for your help.
Click to expand...

I created one for the air and it got one sale. and six hours of assembly time. never again.

Try the 13.7k and see what happens.
 
Status
Not open for further replies.
Top