820-2915-B , chimes but no signal & no backlight

premtec

New member
I have two same 820-2915-B [with 216-0809000] that have same problem, they chime and even start OS [I can hear volume up/down with 10.9] but they give no signal at display and no backlight.
I have disconnected LVDS and tried with display port but without luck.
The first one had lines at display when brought in and I replaced gpu - after that the problem occured. So I reballed the vrams and reflowed the gmux also with no luck.
Next I placed back the old gpu but still nothing happened. The used new gpu had been installed at another one and worked ok [I have a good stock of them] so someting else is happening here.
The second 820-2915-B was received with the exact same issue and neither me or anyone else has meshed with it yet.
About some measurements,

PPVCORE_GPU 1,10 V
LCD_PWR_EN 0V
PPVCORE_S0_AXG 0,45 V

I have to mention that I had before one same case with 216-0810005 gpu but I had to return it as I thought that it wasn't common issue and didn't worth to spend time.
 

dukefawks

Administrator
The first board was probably a badly soldered GPU, but since you messed with the GMUX that will now probably need reballing/replacement.

The second one has not been messed with yet?
 

premtec

New member
I do a lot of bga rework so it would hardly be bad soldering.
Yes, for the second one I haven't spent any time by replacing the chip of anything else as I'm sure there's something else happening here.
The only thing I got some measurements that match with the first board.
Any hints where to start?
 

dukefawks

Administrator
First see if the second board works on external display. I assume you have heated up the GPU to make sure it is not just a simple bad chip.
 

premtec

New member
I had it tested with external display but I hadn't heated it.I did some heating and display came alive! Now I'm replacing the chip.
I didn't have any similar issue with no display because of gpu at this model so it wasn't my practice to heat them.
Any hope for the first board also or not?
 
Top