A1990 820-01326-05 stuck 20v strange voltage fluctuations

[Sdogs]

thank you for allowing me to participate in this Forum, as a hobby I delight in the repair of macbooks, I am a beginner, I have this macbook that I bought to try to get it back in operation.
At the first attempt it turned on it seemed to have a correct absorption of amps and seemed to charge the battery, from the beginning there seemed to be activity as the trackpad seemed to respond to impulses. Obviously it never turned on, no sound, the fans never turned. It does not heat in any point, observed with a thermal imager. A newbie question, does this type of macbook start up with no battery connected?
I tried before and to perform other operations a DFU restore but it was not successful returning errors almost at the end of the process.
The logic shows no signs of the presence of oxides or liquids.
It has a strange behavior, without battery connected it remains stable at 20v but with variable absorption from 0.03A-0.07A if I connect the battery v from 20v to 5v, cyclically.
Here are the measurements I made:

PPBUS_G3H - 12,60v
PPBUS_HS_CPU - 12,60v
PPBUS_HS_OTH5V - 12,60
PP5V_G3S - 5v
PP3V3_G3H_T - 3,3

Also it has a strange behavior, a continuous variation of the voltage on r3460 and r3450, from 0.5v to 1.8v with continuous oscillation, I replaced u3200 and it is now stable on 0.8v

I repeat, I am a beginner, forgive me if I make any mistakes in the description

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[2informaticos]

First of all, welcome to the forum!

You shouldn't touch anything on USB-C area, if got 20V with charger alone.
When measure something on a CD3215 chip, be aware to connect the power on corresponding USB-C port.

Are the SSD voltages present?

BTW, which schematic are you using for diagnose?
Maybe 01041, or 01814?

 

[Sdogs]

sto usando lo schema 01041, sui pin 3 - 4 R5600 3,3v.
r5620 12v on pins 3 - 4

 

[Sdogs]

sorry I'm a beginner, did you mean these values?
are present

PP2V5_NAND_SSD0 = 2,5v

PP1V8_SSD0 = 1,8v

 

[2informaticos]

When you bought the machine, got some kind of history about the failure?

All mentioned voltages are stable in time?

 

[Sdogs]

I bought on EBay, unfortunately I don't know the history of this macbook, I just know that it should be the version with i9 cpu, 32gb ram and 1tb hard disk.
the voltages are stable

 

[Sdogs]

When you bought the machine, got some kind of history about the failure?

All mentioned voltages are stable in time?

also the voltage on r3460 is now fixed at 0.8v

 

[2informaticos]

Don't insist on USB-C area, if all ports switch to 20V.

What is PPBUS_G3H voltage with both charger and battery connected?
Check it when you nothe the glitch on the USB-C ampmeter.

 

[Sdogs]

Don't insist on USB-C area, if all ports switch to 20V.

What is PPBUS_G3H voltage with both charger and battery connected?
Check it when you nothe the glitch on the USB-C ampmeter.

here are two photos of the measures. as soon as the PPBUS_G3H charger is connected it goes to 12.70v but be careful, with the charger and battery connected it stays at 20 volts for a second, then it drops to 5v but PPBUS_G3H remains stable at 12.40v.

 

[2informaticos]

Check for short on all secondary power supplies; diode mode to ground on big coils.

Test the board alone on the desk.
Put the metal protection plate in place, for the USB connector!

BTW, any reason to quote an entire post visible few centimeters above?
Please, maintain the forum aesthetic...

 

[Sdogs]

Check for short on all secondary power supplies; diode mode to ground on big coils.

Test the board alone on the desk.
Put the metal protection plate in place, for the USB connector!

BTW, any reason to quote an entire post visible few centimeters above?
Please, maintain the forum aesthetic...

all those in the cpu and gpu area are short-circuited

 

[2informaticos]

CPU and GPU coils have very low values as normal.
Check all other power rails; on coil, or after Power MOSFETs, when needed.

PLEASE, write directly on the reply box, instead of pressing Reply button!!!

 

[Sdogs]

I'm sorry I'm making a mess, will pay more attention to the answers.
going back to the coil measurements I checked these:
L8102 0.06
L7030 0.43
L7701 0.08
L8410 0.78
LB700 0.26
L7660 0.40

 

[2informaticos]

I'm not sure about L7701 and L8802; look lower than 01041 board.
Unfortunately, cannot compare with same 01236 board; may still be in specs.

Your problem must be related with T2, or SSD.
Do you get 0V9_SSD too?

 

[Sdogs]

in the afternoon I will do further tests, looking in the forum I saw that another user "macRepairAmb" had the same problem, but the post seems to be interrupted, by chance do you know if it solved?
macRepairAmb post

 

[Sdogs]

yes 0V9_SSD present and stable

 

[Sdogs]

Ho notato una strana fluttuazione di tensione ai poli dell'L7030, passa da 4v, poi a quasi 12v, scende a 10v poi a 8v e riparte

 

[Sdogs]

also P1V2_SW is not present, I checked at pin 13 of the U7701 and it seems to be in short circuit, in diode mode it has a value of 0.07.
I don't know if this voltage is needed for booting, is that correct?

 

[2informaticos]

I already said L7701 has lower value than 01041 board.
However, not sure which should be correct value for 01236 board.

1V2_S3 powers on the RAM; it is necessary to boot.
Check U7701 voltage; pins 12, 6, 16, 17.

 

[Sdogs]

Pin 12 5,1v
Pin 6 2,8v to 3,1v oscillating and unstable
Pin 16 0v
Pin 17 0v