820-00923 - Chimes sound loop, no display just backlight - 20V 1.95A

[ronaldo]

Hello everyone.
I need help, please.
Got this Mac in to repair, and it's stuck on chime sound, sound is cycling, video link showing the issue.

It gets backlight, but no display.
BIOS flashed with another Clean ME firmware and still the same.

PPBUS_G3H = 13.3V
PP3V3_G3H = 3.41V
PP3V0_G3H = 3.0V
PP5V_S5 = 5.15V
PP3V3_S5 = 3.3V
PP3V3_SUS = 3.36V
PM_SLP_S5_L = 3.35V
PP1V0_SUS = 1V
PLT_RST_L = 3.36V
ALL_SYS_PWRGD = 3.3V
CPU_VR_EN_R = 3.24V

Diode mode on:
L7430 CPUGT_SW3 - 0
L7420 PPVCCGT_CPU_PH3 - 0
L7410 PPVCCGT_CPU_PH1 - 0
L7210 PPVCC_CPU_PH1 - 0
L7220 PPVCC_CPU_PH2- 0
L7270 CPUVR_SWSA - 0.14
All the other coils are measuring similar to a working board

 

[2informaticos]

How do you get PLT_RST_L high without CPU core voltage?
Please check again...

 

[ronaldo]

The CPU VCORE voltages I mentioned above is for DIODE mode. Not Voltages.

Voltages is.
L7430 PPVCCGT_CPU_PH2 - 0V
L7420 PPVCCGT_CPU_PH3 - 0V
L7410 PPVCCGT_CPU_PH1 - 0Vv
L7210 PPVCC_CPU_PH1 - 1.08V after about 8 secs drops to 0.64V
L7220 PPVCC_CPU_PH2- 1.08V after about 8 secs drops to 0.64V
L7270 CPUVR_SWSA - 1.05V after about 8 secs drops to 0.77 for 6 secs then stays at 0.85V

L8000 - PP1V_PCH_REG_R
L8050 -

 

[2informaticos]

0 in diode mode means pure short; is not same as 0.002 for example.
In the future, post accurate information and avoid missunderstood like above.

Disconnect touch ID and keyboard; see if gets image, or test USB activity.

 

[ronaldo]

I've checked on another working board and measurements in
Diode mode on:
L7430 CPUGT_SW3 - 0
L7420 PPVCCGT_CPU_PH3 - 0
is same as on the faulty logic board.

L7430 CPUGT_SW3 - 3.2 Ohms
L7420 PPVCCGT_CPU_PH3 - 3.2 Ohms
Is this normal?

 

[2informaticos]

CPU core and iGPU coils have very low resistance to ground as normal.

"L7430 CPUGT_SW3 - 3.2 Ohms"
This should be something like 0.002-0.004 in diode mode.
Why do you write just 0???

"L7210 PPVCC_CPU_PH1 - 1.08V after about 8 secs drops to 0.64V"
This voltage should fluctuates, if chimes in loop.
Check if is the case.

Test what happens in SMC bypass and safe mode.
You can try known good BIOS.