A1534 820-00045-A no backlight

[hgoncalves]

Hi,

I have an A1534 820-00045-A with no backlight.

Already tried a known good display, but still no backlight.

I have external image.

PPBUS_S0_LCDBKLT_FUSED = 8.59V
PPBUS_SW_LCDBKLT_PWR = 8.57V
LCDBKLT_EN_L = 8.50V

PPBUS_SW_BKL = 0.451V and 0.395 on diode reading

PPVOUT_S0_LCDBKLT = 0.628V and 0.528 on diode reading

Can you help?

 

[2informaticos]

Only missing backlight, do you get internal image for sure?
Any history available?

Be sure all R7760-3 are good.
Check voltage and diode mode to ground at BKLT_SCL/SDA_R lines.
I hope you've already checked 5V_S0SW_LCD presence.

 

[hgoncalves]

Sudently, while taking mesurements, it started to have image again.

Any ideas about what to check in order to prevent this from happend again?

 

[hgoncalves]

It seams that the display only works, whenI let the mac heat for a while. While it is hot, it works everytime.

When it is powered off for a while, and gets cold, it has no display. However, when I let it heat for a while (even with the board alone on the bench), the display works fine.

Any ideas?

 

[2informaticos]

This MLB model is a nightmare.
You can't discard any weird issue caused by CPU itself.

Just in case, check SMC_LID signal.

 

[hgoncalves]

SMC_LID = 3.252V.

Shal I reflow the CPU?