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820-3332-A A1398 weird power problems

Melvinzill

Melvinzill

Member
Hi, have this A1398 with some super weird problems I?ve never seen before. I got it having a short on PPBUS. This was cleared after removing MOSFET Q7260 which cleared the short. Replaced it with a donor and as soon as I gave it power it got very hot and PPBUS was shorted again. I checked out U7201 and found it outputting 12V to a 5V line. Replaced it and the mosfet with another donor and no more short on PPBUS. Still won?t boot though. U7201 has an Enable of 3.02V instead of normal 3.3 but it does have the supply of 12V. Is the low Enable a Problem? Anyone got any tips? Thanks!
 
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2informaticos

2informaticos

Administrator
Staff member
Welcome to the forum!

Do you really think 3.02V is too low?
If you read many posts, should know that many times we talk about 3V when reffer to 3.3V power rails, or signals.
In fact 2.1V is the min threshold for high logic level (1L); as 0.8V es the max threshold for low logic level (0L).
0.8V-2.1V is a prohibited range, where a logic level is no guaranteed to be recognized correctly.

Burnt U7201 and Q7260 could mean the board is trash now.
Overvoltages on 3V3 and 5V rails is almost letal...
After all, do you get 3V3_S5 and Magsafe light?
 
Melvinzill

Melvinzill

Member
Hi, thanks for your reply!

Yeah, 3.02 should be fine I just wanted to verify. I have a Magsafe Light and PP3V3_S5 is 40mV so basically 0. Any idea on what to do next?

Thanks!
 
Melvinzill

Melvinzill

Member
The Voltages are:

Pin 23 - 12.83V
Pin 12 - 3.312V
Pin 13 - 1.5V
Pin 22 - 1.6V
Pin 29 - 1.2V
Pin 21 - 3.1V

Hope my Multimeter didn't slip on any of these....
 
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Melvinzill

Melvinzill

Member
I did. I Always try avoiding to measure at the chip if possible... Remeasured everything, edited the post with all of the updated values
 
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2informaticos

2informaticos

Administrator
Staff member
Looks like bad U7201 for me; or incorrect solders.
Post first diode mode (red probe at ground) on pins 13, 22, 29; no power, of course.
 
Melvinzill

Melvinzill

Member
The measurements are:

Pin 13 - .47
Pin 22 - OL
Pin 29 - .45


Should I just order up a new U7201 Chip? I mean we don't fully know if the chip off of the donor board was any good...
 
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2informaticos

2informaticos

Administrator
Staff member
Also check diode mode at L7220/60.
If good, change U7201.

Really strange to got bad one from scrap.
Don't you have more donor boards in the pile?
 
Melvinzill

Melvinzill

Member
It comes up as .39 on L7220 and .002 on L7260, is that of any help?

Sadly completely out of donors
 
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2informaticos

2informaticos

Administrator
Staff member
Short on 3V3_S5, because of burnt Q7260.
Looks like scrap board now.

If have time, you can remove U7201 and Q7260; then check diode mode again.
Do NOT power up the board without U7201...
 
Melvinzill

Melvinzill

Member
Removed both. Now .46 on L7220 and still .002 on L7260. Anything I could theoretically try?


Out of pure curiosity: what would happen if I powered it up with those missing parts?
 
2informaticos

2informaticos

Administrator
Staff member
"Out of pure curiosity: what would happen if I powered it up with those missing parts?"
I could tell you try and see ;).
But I'm afraid you can come and kill me, after lockdown time finished :mad:.
Seriously, do not try any of these options...

Leaving Q7220 with Gate floating on air is a really bad idea.

Remaining short after L7260 could mean damaged SMC, PCH, or CPU.
You can try injecting voltage there and check if something gets hot.
Remove CPU heatsink for test.
Start with 1V and do not exceed 4V; leave amp limit at max on the PSU...
 
Melvinzill

Melvinzill

Member
Ah got ya, just wanted to know. Would never try that... I did find something curious though. On the PCH itself there is a tiny Capacitor. When I put my meter in continuity if beeps on both sides of that cap. On my donor it doesn't. Is that relevant? I'll get a new bench PSU (me idiot killed mine yesterday) and try injecting Volatge
 
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