(347) 552-2258 [email protected]

Imac 21.5 late 2013 a1418 (emc 2638) display not working no 4th diagnostic led

F

Funkwarrior

New member
Hello,
I'm trying to repair an iMac A1418 (EMC 2638) which have a display fault.
Seems on cold boot display works on a black screen; the time span is a few minutes before the display fails.
I tried an external monitor and it works, correctly.
The board is a 820-3588-A.

When the display is active and alive, I think all values ??are ok:
Diagnostic LED: # 1 ON # 2 ON # 3 ON # 4 ON

J8100
LED_RETURN_1 4.5V (sometimes 11,5V)
LED_RETURN_2 4,5V (sometimes 11,5V )
LED_RETURN_3 4.5V (sometimes 11,5V)
LED_RETURN_4 4.5V (sometimes 11,5V)
LED_RETURN_5 4,5V (sometimes 11,5V)
LED_RETURN_6 4,5V (sometimes 11,5V)
BKLT_BOOST_1 61,3V
BKLT_BOOST_2 61.4V

L440
PP12V_LCD_F 12,1V
PP12V_LCD 12,1V

When the
LED goes black, I have: Diagnostic LED: # 1 ON # 2 ON # 3 ON # 4 OFF

J8100
All 0V

L440
PP12V_LCD_F 12,1V
PP12V_LCD 12,1V

VSYNC Cable with no sign of shorts.

Any hint?
Thanks
 
2informaticos

2informaticos

Administrator
Staff member
I'm not sure if I correctly understood you.
Always has image, only disappers the backlight?

Did you try known good LCD and video cable?
Reseat video cable on the MLB and the backside of LCD too.

Any history available?
 
F

Funkwarrior

New member
On cold boot always have an image. After random period, i have no image e no backlight.
I have also removed D4450 and replaced C4451 with a jumper (temporarily). Same behavior.
It's the lcd panel?
 
2informaticos

2informaticos

Administrator
Staff member
If image disappears too, try first other display.
Backlight issue should not block the image output.
Looks more like LCD issue...
 
F

Funkwarrior

New member
When the image and backlight both disappears, the 4th check LED goes off. Only chance is to replace the LCD? any chance to repair the lcd?
 
2informaticos

2informaticos

Administrator
Staff member
Try other display first; an LCD issue needs to be confirmed.
Be sure to have good contacts on both sides of video cable.
Also try other video cable.
 
You must log in or register to reply here.
Top