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[SOLVED]820-4924 power cycling

ytesfay80

ytesfay80

Member
I have another 820-4924 that is having a similar issue as one I had previously posted about except this one had liquid damage. The customer said it came in contact with rain and they had the corrosion cleaned at a local shop(looked like they just ipa and brushed it and not ultrasonic). I ultrasonic'd the board and still no change.
Previous board with similar issue: https://www.rossmanngroup.com/boards...not-turning-on

Customer's Note: "It was water damaged in moderate rain, left vertical in a backpack. An anti-corrosion treatment at Retech saw it working again for a month before the working laptop stopped charging and the battery drained."

I get a green light that turns orange so I assume 3v42 is fine.
PPBUS_G3H starts at 13.69v(not sure why its so high) then quickly goes down to around 3v then back up to 13.69v and repeats
PP5V_S5/S3/S0, PPVCC_S0_CPU all keep cycling from there original voltages.
U1950 looks good and Pin 2 also cycles. U6100 looks like there was liquid near there but no corrosion visible and the traces look great.
I replaced some components most of which were connected to PPBUS_S5_HS_COMPUTING due to some bad looking caps.
Replaced C7317/18, C7310/11,R7311,U7310, C7620/22
U7200 Pins 7-10 didn't look good so I replaced the entire chip but that still didn't solve this.
 
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Alan.L

Alan.L

Member
power cycling or pulsing voltages are sucks, they can be anything when there are no visible damage on the board. i hate fixing these boards. i hope you can fix it. :)
 
ytesfay80

ytesfay80

Member
This board does have some visible damage since it came in contact with liquid. What are the most common areas to look for with this issue?
 
ytesfay80

ytesfay80

Member
The U6100 termination resistors all measured fine and the traces as well, I replaced the clock chip and u1950 even though they looked fine. I put another bios on the board and it still does the cycling.
I replaced Q7630,C7630,C7624, and R7631 since they didn't look to great and the board is still doing the same thing.

What else do you think could be causing this?
 
G.Beard

G.Beard

New member
ytesfay80 said:
The U6100 termination resistors all measured fine and the traces as well, I replaced the clock chip and u1950 even though they looked fine. I put another bios on the board and it still does the cycling.
I replaced Q7630,C7630,C7624, and R7631 since they didn't look to great and the board is still doing the same thing.

What else do you think could be causing this?
Click to expand...

What do PPBUS and S5 rails do when the board is not trying to power on, i.e. With only the battery connected?
This will not lead me to be able to answer questions but it may eliminate possible causes in your hunt for the fault.
 
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Gurmon

Gurmon

Member
Its time to start providing diode mode readings to all power rails. This may help in identifying shorts.
 
ytesfay80

ytesfay80

Member
When I plugged the battery in PPBUS_G3H on R7005 was around 2.2v and quickly went towards 1.55v and stayed around there. PP5V_S5 showed 0v.
 
ytesfay80

ytesfay80

Member
I checked the sense resistors and it was way too high then I noticed that the caps/resistors looked a little dark so I replaced the entire area as well as the ISL6259. Now PPBUS is steady 12.6v and cpu vcore/5v_s0 was steady as well.
I can feel the cpu getting warm so I know its turning on but for some reason the screen is not showing anything. I plugged in a known working late 2013 screen and that didn't turn on either. I'm not too familiar with the screen circuit for these Retinas but here are some measurements I got from the lcd connector.

J8300- Pins 3/4 - 5.15v
Pins 1 and 28/29/30 all gave me 0v
 
ytesfay80

ytesfay80

Member
Okay I plugged in my spare keyboard and did the pram reset but nothing happened. I'm pretty sure the keyboard is working because I measured the kbd connector pins as I clicked the option key and the control key and they both went up to 3.42v as I pressed them.
I also tried to do the smc bypass and hook thunderbolt to my tv but that didn't work either.
 
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D

dukefawks

Administrator
You use a USB keyboard to do this....Who know if the trackpad is even working which is needed for the keyboard to work.
 
ytesfay80

ytesfay80

Member
okay I didnt know the trackpad has to be working for the kbd to work. I plugged in my usb mouse again and I got no lights so I went and checked voltages again and found out there is no vcore or s3/s0 rails. 5v_S5 is present so now I have to figure why the rest of them aren't.

As far as the usb keyboard does it have to be an apple one? The only one I have is a very old Dell usb keyboard.

Update:
Here are some measurements I got from u7501 which lead me to finding out there is no voltage on PM_SLP_S4_L
Pins 12,22,23 and 29 all have the correct voltages present
Pins 20/21 had 3.4v
Pins 2,4,5 show 0v as well as 0v on R8179
 
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D

dukefawks

Administrator
I have no idea what you are doing. Now there is even no S3 power? I'm sorry but I have no idea what is going on here....
 
ytesfay80

ytesfay80

Member
Alright with no external components plugged in I measured PM_SLP_S4_L as soon as I plug the charger in and I saw it show 3.4v for a quick second. Do you know what would usually cause it to pulse like that?

I did replace u1900 and u1950 when I was first diagnosing the board so I'm not sure if this could have caused any of these problems.
 
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D

dukefawks

Administrator
Yes anything can cause power cycling, the usual are the clock chip, U1950 and U6100 termination resistors and traces. Check all traces between U6100 and the resistors too!!
 
ytesfay80

ytesfay80

Member
Okay so Q7310 didn't look too well on the Pin 5 side so I replaced it along with Q7311 for good measure and now it turns on and runs perfectly fine. Thanks
Do you have an idea how that could have caused these issues?
 
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