[SOLVED] 820-3476 Help a beginner

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rob777

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Hey guys, just diving in to board level laptop repairs here, I purchased a dead water damaged Macbook Air and also this Retina 13in to begin my learning quest. Macbook Air was repaired after hours and hours of watching Louis's videos which I'm absolutely stoked about! Thanks Louis! But now this 820-3476 board is giving me issues. So I'm here to get some pointers hopefully..

Firstly the laptop would not power, no orange, no green lights. Dead in every aspect. Found some minor corrosion around C7050 and C7060. Replaced C7060 and cleaned the rest in the ultrasonic. Now I have orange and green lights and the fans spin so I reassembled into laptop.

Although I get the orange light and fans come on I still get no chime and nothing on the screen. After a couple mins the fan starts going extreme.

I then started measuring power rails, everything is present.

Does anyone have any suggestions on where I should start looking now? I feel like I was making progress in my learning here but have hit a pretty big wall and am stumped basically.

Going to study the way the LCD works over lunch and see if that can give me some insight otherwise any pushes in the right direction would be lovely!

Thanks
Rob
 

larossmann

Administrator
Staff member
does it work with thunderbolt to vga adapter into a monitor, give you a questionmark folder? does it light a USB mouse?
 

rob777

New member
hey mate, thanks for the reply. Confidence has gone from sky high to rock bottom here..

To answer your questions, only have thunderbolt to hdmi so can't test that. No there is no question mark folder (LCD doesn't seem to even show a backlight) and when I plug in a USB mouse it lights up for half a second.

I have started from scratch again, testing the one wire circuit and power rails. Now please correct me if I'm wrong or if my thinking is way off track. I think my learning curve is just starting to rise now..

U7090 Pin 6 vin should be 3.42v right? It gets it from D7005 which has 14.5v on pin 1, pin 2 and pin 3, the 3 resistors C7092 C7091 C7090 all make sure U7090 gets the correct 3.42v?

My VIN on PIN 6 of U7090 is still the 14.5v measured from D7005. So do I have a part that isn't pulling the voltage down to 3.42v? Is D7005 not doing its job?
 

rob777

New member
also seen one of you videos where you describe it as a possible cpu vcore issue? When there is no chime.. Need to try find that vid next I think.
 

larossmann

Administrator
Staff member
if it turns on from a charger who cares about onewire circuit, we need brain. why check the onewire circuit if it has power from a charger? look at the purpose of that circuit.

think of this like heart and brain. heart is working, it turns on. now we need brain(light on mouse, chime, etc)
 

rob777

New member
I'm lost, 5hrs down and counting here.. Determination definitely isn't the issue. Alas I have no idea why the CPU isn't working and I have no idea what to look at next. The vcore power rail exists. Being only my second ever attempt at repairing boards I obviously have a fuck load of learning left to do.

Any more subtle tips to try and help push me in the right direction? Thanks
 

rob777

New member
I'll continue this tomorrow with a fresh brain and a different approach. Been a 13hr day here, going home to refresh on all Louis's videos again.
 

rob777

New member
Ok so the cpu doesn't seem to be getting ppvcc_s0_cpu

Follow it back to U7310 and u7320. They both have very low readings from pins 2,1,8,5. Pin 6 is showing pp5v_s0.

But those pins go to a transistor so at pin 2 of L7310 and L7320 I should have 1.8v. But I don't.

Gonna leave it for now. Come back again when my brain comes up with any new knowledge.
 

dukefawks

Administrator
Where was the corrosion? There is no CPU Vcore because the regulator is not told to turn on. Probably corrosion on resistors from SPI ROM, or crap around clock chip.
 

rob777

New member
Was very minor corrosion around c7050 c7060 (above battery connector) and I replaced one of them and got the green light back.
 

rob777

New member
Giving up. Repairing this is beyond me it seems. Gonna eBay the board as is with NFI what's wrong.
 

rob777

New member
R6110 r6120 test fine.
I found that I do have:
Spi_mlb_cs_l
Spi_mlb_clk
Spi_mlb_miso
Spi_mlb_mosi
Spi_cso_l

There were a couple other spi lines I can't remember as well but no problems found.
Thanks for your time here though!
 

rob777

New member
For fuck fucking sake. It's fixed.
These things don't chime when you turn them on. Have tested on 3 others now.
My problem was the lcd cable. I changed lcd cable. Still didn't chime. Swore a few more thousand times looked at laptop and low and behold. It's fucking working. Perfectly.

Thank fuck for persistence.
 

dukefawks

Administrator
Yes they do chime, do a PRAM reset. If the volume was turned down on the last time it was booted there will be no chime.
 
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