820-3330 no CPU VCORE

[Dozer]

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.

 

[aprendiz]

If you replace PCH now you need a bios with clean ME region.....

 

[Dozer]

could you help me to clean the me region in the bios?
here is the original reading

https://www.dropbox.com/s/rqd28gica3e4gw4/S06735_3330_original - Kopie.bin?dl=0

 

[dukefawks]

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

 

[Dozer]

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]

here still the values measured in diode mode red on gdn on u7400 and compared with a known working one

820-3330
U7400
Pin	badboard	godboard	diff.
1	648	651	3
2	14	15	1
3	647	652	5
4	80	80	0
5	4	4	0
6	651	654	3
7	14	15	1
8	101	101	0
9	53	51	-2
10	10	10	0
11	51	51	0
12	566	562	-4
13	541	543	2
14	586	586	0
15	5	6	1
16	661	661	0
17	4	4	0
18	455	450	-5
19	387	385	-2
20	4	4	0
21	77	76	-1
22	87	86	-1
23	67	66	-1
24	546	541	-5
25	585	582	-3
26	6	5	-1
27	663	661	-2
28	463	450	-13
29	387	385	-2
30	3	4	1
31	458	453	-5
32	662	661	-1
33	5	6	1
34	586	583	-3
35	587	578	-9
36	567	558	-9
37	549	543	-6
38	666	664	-2
39	569	561	-8
40	658	656	-2
41	101	100	-1
42	50	51	1
43	8	8	0
44	44	45	1
45	44	45	1
46	393	390	-3
47	460	445	-15
48	647	645	-2

 

[Dozer]

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.

 

[Dozer]

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...

 

[Dozer]

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?