820-3330-B No Boot Warm GPU

[sangolossyfon]

Board has good PPBUS_G3H(14.6v) and 3V42(3.92v)

5VS5, S3, and S0, as well as 3V3 S5, S3, and S0 are all good, at 5.87 os 3.86v.

When power applied board draws about 6w but does nothing, no fans.

In SMC bypass, fans run and board draws about 8w.

GPU_VCORE fluctuates slightly around 1v.

PPVCORE_S0_CPU has 0v, so does S0_AXG.

However VCORE and AXG resistance to ground is identical to a working board. slightly over an ohm.
also 0v on PP1V05_S0 and PP1V5_S3RS0. But resistance on these circuits also matches working board. 170 and 7.5 ohms.
tried reflowing cpu and gpu.
any thoughts? if this seems like a time-consuming fix I don't want to get into it.thanks for any help.

 

[2informaticos]

Do you get ALL_SYS_PWRGD?

 

[sangolossyfon]

it stays at 0v. even in SMC bypass mode still 0v.

 

[2informaticos]

Post all voltages you get on the coils.

 

[sangolossyfon]

all L75xx & L76xx have 0v both sides

still 0v in SMC bypass

L89xx have 0.89v

L7330 1.5v

L8310 1v

L7220 5v

 

[2informaticos]

L7100/630/720/730/760/770???
Also check all voltages from page 73.

 

[sangolossyfon]

7100 0.89v
7630 0v
7720 1.8v
7730 1.15v
7760 0.04v
7770 1.5v
If you were referring to page 73 and not sheet 73-
U7300
12 5v
17 0v
16 3.3v
6 1.8v
8 1.5v
19 0v
18 0.68
15 6.58
14
13 1.5
11
20 0.06
9 1.8
3 0v
1
5 0.74

If you were referring to sheet 73-
PP3V3_S3_FET 3.3v
PP5V_S5_P5VSUSFET 5v
PP3V3_S0GPU_FET 3.3v
otherFETs were not in boardview

 

[2informaticos]

"7630 0v"
That's the problem!
First, check diode mode to ground there; compare with good board.
Post U7600 basic voltages: pins 13, 14, 3.

 

[sangolossyfon]

diode mode to ground on both sides of L7630 is 009 which is identical to working board.
13 5v
14 5v
3 3.3v

 

[2informaticos]

If all components and traces around U7600 are good, then replace the chip.

 

[sangolossyfon]

C6703 WAS LOOSE- and had ripped a pad

BOARD BOOTS after replacing it!

thank you so much for the help! this is a great save!