820-3330 no CPU VCORE

Dozer

Member
hello friends,

i am just working on a 820-3330 board. got it from client, he had it in a apple service for repair and after that it was in boot loop.
i tryed to start asd but after some tryes it was dead only green light and one tick fan spin.

I replaced bios, then smc then U1800. After that I had fan-spin. after that i replaced the original bios back.

all power rails are present only PPVCORE_S0_CPU and PPVCORE_S0_AXG_REG missing.

macbook starts with fan spin and led is all time on.

PPCPUVCCIO_S0_REG is present, CPUIMVP_VR_ON has 3.3V

PPVIN_S0_CPUIMVP = 12.53V

PP5V_S0_CPUIMVP_VCC present

CPU_VIDSCLK is there

TON resistors both are ok (180K) voltage on one side 12.53, other 0,53V, compared with a working 3330, same values.

to be shure swaped with a working 3330 the u7400 but no change, the working one works with u7400 from the problem board.

need some help please.
 
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dukefawks

Administrator
Could be anything really. Any history to this board, water?
ME region has nothing to do with Vcore at this moment.
 

Dozer

Member
no watermarks.
after power on no display, as well extern, nothing, but working.
after a lot of new starts possible to get a picture but only for a while

then the macbook was in apple service to repair.

after that there was a boot loop until the long dong

then it came to me, I tempered the board for 48 houres

after some tryes to start up it dosnt started at all

I replaced SMC, found under SMC 2 popcorn effects. but not shure if it was from me from lift off.

I tryed with another bios chip from a known working 3330. I tryed the bios chip from tha bad board on the working board, got fan spin on the working machine.

I put back the bios chip on the not working board and replaced the U1800. after that i got fan spin with all power rails present only missing PPVCORE_S0_CPU and PPVCORE_S0_AXG_REG

I found out that pin 7 (CPU_AXG_SENSE_R´) from R7400 hat in Diode mode 0.670 and on the working board is 0.015. I lifted U7400, No change.
I reflowed the CPU. After that Pin 7 was 0.015 like it should be.

I soldered back u7400 but still nothing.

thats the history until now.
 

Dozer

Member
here still the values measured in diode mode red on gdn on u7400 and compared with a known working one
820-3330
U7400
Pinbadboardgodboarddiff.
16486513
214151
36476525
480800
5440
66516543
714151
81011010
95351-2
1010100
1151510
12566562-4
135415432
145865860
15561
166616610
17440
18455450-5
19387385-2
20440
217776-1
228786-1
236766-1
24546541-5
25585582-3
2665-1
27663661-2
28463450-13
29387385-2
30341
31458453-5
32662661-1
33561
34586583-3
35587578-9
36567558-9
37549543-6
38666664-2
39569561-8
40658656-2
41101100-1
4250511
43880
4444451
4544451
46393390-3
47460445-15
48647645-2
 
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Dozer

Member
pin 47 has a big diff. I still found another working board and there has pin 47 463. So that could be ok.

just again doublechecked, 3.3V is present on that pin 47, the eneable pin.
 
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Dozer

Member
any idea where to start diagnostic?

what happens after CPUIMVP_VR_ON has 3.3V, which signals or clocks have to be there that the u7400 starts work?


I get on pin 6 U5400 only 0.07V, the good board shows 0.22V, on U5410 pin 6 I get on the bad board 0,19V that should be ok
but U5400 ? only 0.07V on Pin6 ?

Pin4,5 have 12.55V, pin 3 has 3.3V, I replaced U5400 but same values...
 
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Dozer

Member
I just touched the U1800 and damn so hot, burned my finger :).

Is it a good idea to replace it again? If its hot because of a short of any rail so why i have a fan spin?
 
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