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820-3787 No video internal or external HDMI but chimes and fans turn on usb activity

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bradinboise

Member
Hello all,

I got this one in and it is very clean inside, no signs of liquid damage.

I started testing voltages and I have 0v on the PPVCORE_GPU. Diode tested 0v. Short to ground. Is this normally a shorted bad GPU? Should I throw this in the parts bin?

Thanks again.
 
2informaticos

2informaticos

Administrator
Staff member
A real short should turn off the baord.
GPU power supply is maybe not even enabled.
A very low value is normal there.
Post exact value, ohm scale.
Compare with working board.
 
B

bradinboise

Member
Thanks for the fast reply.

I measure .5 ohms on that line. FYI I forgot to mention earlier that this is the board w/discreet graphics. I do not have a similar board lying around to compare to.

So do you think that reading is bad enough to called it a shorted-bad GPU?

Thanks
 
B

bradinboise

Member
Ok, I wanted to make sure my DVOM was accurate, so I borrowed a friends newer DVOM and went through all the rails again to verify. And there were some different readings. So the PPVCORE_GPU is still reading 0v however my diode test is .008v and ohms are 5 ohms instead of .5 ohms. Bad meter and or leads I'm guessing.

So all my rails are ok except the following below:

PPBUS_SW_BKL 0v (12.6v spec)
PP15V_TBT 0v (15v)
PP3V3_S0GPU .5v (3.3v) no short to ground
PP3V3_S0GPU_MISC .5v (3.3v) no short to ground
PP1V5R1V35_S0GPU 0v (1.5v) 1.2 ohms to ground .003v diode mode
PP1V0_S0GPU_ISNS ov (1.05v) 189 ohms to ground .106v diode mode

This unit will do a SMC reset and a PRAM reset like normal.

Using a flashlight I cannot see anything on the screen either. I'm not sure if the screen actually works. I picked it up at an auction so no history either.

Thanks
 
B

bradinboise

Member
Ok, started back into the GPU power sequence on page 66. Did not get very far since the first in the sequence:

EG_RAIL1_EN = 0V (3.3v spec) .640v diode and 17.6 K ohms to ground so no short.

It looks like to me this 1st voltage comes out of the U9600? I checked all the voltage inputs to the U9600 and all are there.

Could that U9600 be the cause? Does this chip have firmware? If yes, do you know by chance what other boards I can rob from?

One of the things I cannot figure out with the U9600 is what line(s) turn that chip on? Just wanted to make sure I was checking what I can before going that route if indeed the U9600 is at fault here.

Thanks
 
2informaticos

2informaticos

Administrator
Staff member
U9600 GMUX has firmware.

I still think on GPU issue.
Heat it for test.
You can also try to reflow GMUX.
 
B

bradinboise

Member
Thanks, as far as heating the GPU, what heat value degree and how many seconds would you recommend heating the GPU to test? Also would you use flux or just heat?

Thanks
 
2informaticos

2informaticos

Administrator
Staff member
Only heat Si die; no need to melt the balls.
A real 150 degrees on the chip, should be good enough.
You may need to set 400 on hot air station and a convenient distance...
 
B

bradinboise

Member
Well neither one of those suggestions did anything, darn it. I would have to agree with you that the GPU is at fault here.

I went ahead and purchased another board that they say works and I'll first install that when I get it Monday. To make sure the screen on this one works.

I'm going to compare readings with the 2 boards and if I find something I will come back and report it for others if needed.

Thanks
 
B

bradinboise

Member
Does anybody know if I can use a A1502 screen for testing purposes on a A1398 macbook pro? I have a 2015 and a 2014 A1502 screen I use for testing A1502 models. Just don't want to short out the board I just got for this 2013/2014 Macbook Pro 15".

By the way, the HDMI works now with this different board but the screen still doesn't light up or work using a flashlight.

Thanks
 
B

bradinboise

Member
Another note, the logic board I just received I noticed that C8350 and C8353 are missing?? Looks like they broke off next to J8300 video connector. I wonder if they ran this too long in the ultrasonic cleaner??

These capacitors are the LED1 and LED4 return to U7750. Will these missing caps cause my screen to still not light up and work?? Everything else on the board seems to work, so I'm contemplating installing those caps or just sending it back for a refund.

Thanks
 
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