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820-2879 not turning on

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Fizzl92

Member
Hello,
i am working on a 820-2879 that is not turning on. I fixed the green light (isl6259. was burned) and now Q7085 won´t open. In fact it opens for 2-3 seconds (than ppbus_g3h is there and 16V can pass q7085 because the Gate is 6.6V) but than the Voltage on the gate jumps to 15.5V and Q7085 closes. I checked R7085 (0,471MOhm), R7086 (331KOhm), R7020 (5,4Ohm), R7021 (15,5Ohm) and R7022 (15,3Ohm). This should be fine i assume. Now i don´t know what to check next.
Thanks for any help
 
F

Fizzl92

Member
I replaced U7000 again and run all the jumpers new. Same as before except that i now get 14,5V on the gate of Q7085 instead of 15,5V.
 

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Fizzl92

Member
I just saw i that i forget to mention that the problem was caused by water damage originally. Sorry for that. Voltage on C7005 is 16,25V and after a few seconds it goes up to 16,53V. I guess that is ok. I thought that Q7085 should be ok as it is able to switch on and off depending on the gate voltage. But to be sure i exchanged it but still the same behaviour with 15V on the gate. I measured around and also plugged in the battery. With only battery Q7085 has 9-10V on all pins (my battery could be a bit low) Also ppbus_g3h is 11V wiht only battery. If i plug charger and Battery in Q7085 has 6,6V on gate and lets the 16V pass. Also ppbus _g3h is 12,6V if both is plugged in. Is that normal on an older board like this? But if i short pads of R5015 with both plugged in it still wont turn on.
 
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dukefawks

Administrator
If the issue is only around U7000 this board should power on from a charged battery. Connect a battery with charge and see if it can power on. Also check resistance to GND on 3V42 bus and RTC Xtal pins.
 
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Fizzl92

Member
I tryed a battery with ebought power to start other boards but no sign of life. Resistance to GND on PP3V42 is 0,021V in diode mode. On RTC XTALIN (Pin 1 of Y2810) i get 0,018V and on RTC XTALOUT 0,007V. Also i recognized, that even with battery and charger both plugged in there are no S5 rails and i just get a green, not a orange light.
 
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