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820-2879: PPBUS_G3H drops slowly from 12.4 volts

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pauly341

New member
Greetings. I'm having this similar issue with multiple boards and I always end up chasing my tail - so wanted to start fresh before I started replacing stuff.

When the board is connected to AC only, PPBUS_G3H measures 12.4v but then starts decreasing by about 1 volt per second. No issue once battery is connected. On other boards, I've replaced u7000, u6990, multiple resistors and caps around these ICs but no luck. Should I be thinking about some other type of component failure such as a coil?

thanks,
Paul
 
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dukefawks

Administrator
Resistance between pin 17/18 and 27/28 of U7000? All power removed of course and make sure to give it some time to discharge.

The machine does power on from a charged battery?
 
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pauly341

New member
17/18 = 2.9 ohms
27/28 = 20.2 ohms

It does power on from a charged battery

discharged for about 4 hours
 
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pauly341

New member
I replaced all three, issue remains.

A bit of clarification, The voltage starts at 12.44v and slowly decreases to 5V (it takes 45 seconds) and then immediately jumps back to 12.44 volts. The cycle then restarts.
Also, SMC_BC_ACOK flips between 3.3v and 3v constantly. I checked SMC pullup resistor and it is good.
 
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