820-3332 no backlight

MegaObi

Member
Hey guys,

very upset on this one. I checked fuse - got excited for the one time fuse was screwed so i thought oh wow - easy repair for once. changed fuse - next minute smoke coming out of lcd connector :(

what do you think caused it - should i try again with new fuse and connector?
 

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2informaticos

Administrator
Staff member
Bad contact inside LCD connector.
Change connector and check video cable terminal too.
Insert video cable and check for short/low value on corresponding pin (to ground).
If OK, change the fuse and turn it on.
 

MegaObi

Member
I changed lcd connector. pluged in screen checked for short to ground nothing changed fuse - and POF! AGAIN!
is 260ohm too low?
 

2informaticos

Administrator
Staff member
"check for short/low value"
I adviced you about low value too...

Did you check the video cable terminal?
Inspect it on both sides; better to change it.
 

MegaObi

Member
im not confident to change cable on retina display.
yes you advised correct.

when you say check video cable you mean inspection? i have pin 1 now burnt i rebuilt with another pin and some uv curing.
 

2informaticos

Administrator
Staff member
You must check resistance to ground at pin 1 of J9000 once LCD cable is inserted.
You must get practically the same value as when LCD is disconnected...
 

MegaObi

Member
55.3k with no lcd connected.
54.6k with lcd connected

i havent replaced fuse yet but i pulled off board.

scared to put back! :cool:
 

MegaObi

Member
good thing is no smoke this time! still no backlight

UPDATE:

lcdbklt_en_l 11.72v
lcdbklt_en 0v
lcdbklt_en_div 11.9v

ppbus_s0_bklt_fused 12.4v
ppbus_sw_lcdbklt_pwr 0v
ppvout_s0_lcdbklt 56v

bklt_plt_rst_l 3.3v

pp5v_s0 5.1v
pp3v3_s0 3.3v

R9708 44k ???? 1%?
R9709 43.5k ???? 1%?
 
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2informaticos

Administrator
Staff member
Why would you expect to get exact reading for onboard resistors???
Surrounding components alter the onboard test.

"still no backlight"
Do you get image at least?

"ppvout_s0_lcdbklt 56v"
How, if you don't get backlight enable?

56V output means no contact with LEDs strip from display; correct voltage 39V aprox.
Check for same voltage at pin 1/J9000.
Try known good (and compatible) LCD assembly.
 

MegaObi

Member
hey informaticos. i dont expect exact reading but expected reading should be closes to tolerance.

yes i do have image

I am not sure how i had 56v before but now when i check pin 1 its 12.05v

thanks
 

2informaticos

Administrator
Staff member
"expected reading should be closes to tolerance"
Not true; reading depends by the other resistors, or ICs, in contact with measured resistor.
Closed loops through ground will create parallel resistors.
For high values, even positive power rail close the loop.

"Try known good (and compatible) LCD assembly."
???
 

2informaticos

Administrator
Staff member
"i check pin 1 its 12.05v"
This means you have LCD_BKLT_EN present; automatically BKLT_EN too.

Post again voltages for U9701 and Q9706/07.
Please provide accurate information, or any help is useless...
 

MegaObi

Member
u9701
2 = 2.5v
3 = 0v
4= 3.1v
5 = 0v
6 = 0v
7 = 0v
8 = 3.3v
9 = 0v
10 = 3.3v
11 = 3.3v
12 = cycling
13 = .3v
14 = .3v
15 = 0v
16 = .3v
17 = cycling
18 = cycling
19 = 0v
20 = 0v
21 = 5.9v
22 = 5v
23 = cycling
24 = cycling

Q9706
1/2/4/5/6 = 12.66v
3 = 4.12v

Q9707
2 = 3.3v
3/4 = 0v
5 = 3.3v
6 = 0v
 
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2informaticos

Administrator
Staff member
U9701 gets all necessary signals and power.
Check R9708/09 and all 6 return resistors.
Verify all traces and solders.
Try again another known good (compatible) screen; allow 1 minute before measure.

Remember, all voltages/signals MUST be measured with LCD connected.
 
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MegaObi

Member
r9708/09 45/47k resistance
return resistors all have around .4v
pins 3-8 on j9000 also have .4 so i think traces good.
i will try another lcd
 
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