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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
 
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Fizzl92

Member
R7005 is 22Ohm. Resistance between Pins 27 and 28 of u7000 is 25,5Ohm and between Pin 17 and 18 is 18.7Ohms. Pins 16, 17 and 18 of u7000 were burned and i need to run jumpers there. As far as i can tell my soldering should be ok because i can not move the jumpers on both sides. So i assume they should be soldered on to the chip. Can this cause the problem?
 

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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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  • ISL6259AHRTZ jumpers.jpg
    ISL6259AHRTZ jumpers.jpg
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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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