820-00840 20V 0 Amps

brunomotter

Member
Hello. Got this machine here with no power. Costumer says he tried to upgrade the SSD at home and after that the machine stopped working. He says he disconnected power from battery before putting on the new SSD. I tested the SSD on another machine and it works fine, so no shorted SSD. Removed the board and testing it alone on the bench only with charger plugged in. Board takes 20V but 0 amps. PP3V3_S5 is jumping up and down like crazy but has no short on it. Though, I could find some shorts. SSD_PWR_EN_CONN_L is shorted, also PP1V8_S5G and PP1V_S5G_REG. Tried lifting L8060 and even without it I cannot get steady PP3V3_S5. Anything else I can measure here?
 
Last edited:

2informaticos

Administrator
Staff member
The client forced the SSD connector, or other thing on the board, to generate shorts.

Remove U8640 and check again 1V8_S5G power rail.
For 1V_S5G the suspects are U8230/60/80; if the short remains on pin2 of L8060.
 

brunomotter

Member
Diode mode:

SSD_PWR_EN_CONN_L - 0.001
PP1V8_S5G - 0.001
PP1V_S5G_REG - 0.000

FULL short on all. Tried injecting voltage on this rails... Nome of them pull more than 1 amp @1V
 

2informaticos

Administrator
Staff member
Did you set amp limit to max on lab PSU?
Also, use powerful cables; you don't want to heat the cables, but damaged component.
 

brunomotter

Member
Yes, PSU current set to maximum, same cables I always use for repairs, which work 100%. My PSU can supply up to 5 amps.
 

2informaticos

Administrator
Staff member
Pure short may need more than 5A.
In such case, your PSU gets blocked and doesn't inject any voltage.
You have some time working with Apple stuff; get 20A PSU for this purpose...
 

brunomotter

Member
Actually, when my bench PSU cannot supply sufficient current its display show 5.5amps being pulled with a voltage drop. For example, if I set it to 5V 5A and there's a short on the board, the amp meter from the PSU says 5.5A which is the maximum it can supply but the voltage indicator drops to less than 1V. This is not happening here on this specific board. If I set it to 1V to inject on those lines some of them pull 0.5A and on L8060 PIN2 it pulls around 1A but with no voltage drop. That's what's strange. It's behaving like I had no shorts on the board. I'll see the possibility of acquiring a more powerful PSU but I really think it would not help much here because as I told, the PSU is not "cutting" it's steady 1V and 1A
 

brunomotter

Member
Yes, I thought it might be some charged capacitor or something like that. The board is sitting on the bench since yesterday unplugged and is still shorted.
 

2informaticos

Administrator
Staff member
Lower than 1 ohm short, must take more than 1A; when inject 1V.
You can go until 1.3V without risk.
Use cables with less resistance possible; is VERY important for low voltage.
 

brunomotter

Member
I raised voltage to 1.3V, it's pulling around 1,40 to 1,60 amps at this voltage. Still, nothing gets hot to touch although it seems PCH gets a little warm, but I think it's normal as it's getting power. Cables are not the problem, because if I put the GND cable on GND and the V+ cable also on GND at another point of the board at the same voltage the PSU delivers 5.5 amps and drops the voltage as expected.
 

brunomotter

Member
I decided to measure resistance to GND on those lines instead of using diode mode. Black probe on GND, red probe on line. These are results:

PP1V_S5G_REG - 2.8 ohms
SSD_PWR_EN_CONN_L - 1.8 ohms
PP1V8_S5G - 0.2 ohms
 

brunomotter

Member
Misteriously PP1V8_S5G line started pulling current(around 3,5A) from PSU, PCH got hot(not REALLY hot, but got hot to touch), after some time the current dropped to 0.5A and PCH stopped heating. Injected 1.2V again on PP1V_S5G_REG and it's pulling now 3.5A from PSU and PCH gets hot on that line. Decided to plug in charger again. Now it's behaving differently. Before it was pulling 0 amps from charger, now it's pulling some current(around 80mA) and PP3V3_S5 got stabilized somehow, still no power though. This board is acting like a nightmare.
 
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