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820-3115-B gets power, fan spin but shuts off after a moment?

H

Hardwood T/S

Member
EDIT 820-2936-B board, 13", board receives power well but when power button is pressed the fan will whir and the sleep light will come on for a moment, then abruptly cut off.

When I keep only the charger plugged in instead of the battery, eventually after many cycles of doing the above the sleep light will blink in sequence 3 times, as if it were indicating a RAM issue. I've tried different sticks tho of course.

No signs of water damage on the board, could it potentially be a bad RAM slot/cartridge? Machine never beeps or indicates anything other than the 3 sleep light blinks, but mostly it's just the brief cut on/cut off cycle.
Plan to test the main power rails tomorrow, but was wondering if you guys knew what it could be/what direction to push me in.

Thanks!
 
Last edited:
2informaticos

2informaticos

Administrator
Staff member
Board should start and get voltages without RAM.
Check if all secondary voltages try to appear at least.
Be sure 3V42 and PPBUS_G3H are stable, as other voltages too.
Check for short on all S3 and S0 rails.
ALL_SYS_PWRGD appears?
 
H

Hardwood T/S

Member
Sorry, it's an 820-2936-B board! Dealing with so many 2012s lately it slipped my mind.
G3H bounces between 12.6v and 4.0v, PWRGD starts at ~3.2v, holds for a few moments and then drops to 3mv bc of the power cycle. 3V42 is stable. Maybe U7000?
5V_S3, 5V_S0, 3V3_S3 AND 3V3_S0 are all present before the power cycle happens, same thing w/PWRGD where it holds for a few moments then drops.
 
2informaticos

2informaticos

Administrator
Staff member
Looks like SMC detects something and resets ISL6259.
Does it stay on in SMC bypass mode?
Post exact resistance between pins 17/18 and 27/28 of ISL6259.
Does it charge the battery?
 
H

Hardwood T/S

Member
It does stay on in SMC bypass mode! I should remember to troubleshoot that when I see problems like these.
So I did a bit of further troubleshooting:

Tried multiple batteries before, all of which didn't work. Got a fresh new battery with a charge today tho to test, the machine boots just fine with a battery. No beeps, nothing awry, you get a chime and everything.
Just with AC, computer does not turn on fully. Also doesn't charge the battery, never changes from green.
How would I test resistance on those pins? They're way too small for my multimeter to reach accurately.
 
2informaticos

2informaticos

Administrator
Staff member
Get special SMD probes for your DMM; few bucks on eBay.

You can measure direct on the caps connected to these pins.
But this will not discard bad solders on the ISL6259.
 
H

Hardwood T/S

Member
In resistance mode I checked C7020, since pad 1 was pin 27 and pad 2 was pin 28--I got 20ohms, but I'm guessing that's just the inherent resistance of the capacitor.
You think it's either a bad U7000 or bad SMC at this point?

I'll get those probes tho!
 
J

JohnB8812

New member
300 ohms is too high. This means one of three things:
1. R7051/2 are either both blown or one is blown
2. R7050 is blown (way less likely)
The trace(s) between the ISL and R7051/2 are blown or between R7051/2 and R7050
 
H

Hardwood T/S

Member
Yeah, it was R7052!! Thanks a bunch guys! While I was taking it off I accidentally ripped the solder pad, so I ran a jumper wire. You guys are the best :) thanks again!! Now I just have to resolder a display connector since I had relegated this guy to parts earlier... lol :)
 
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