[SOLVED]820-2850 weird charging problem - Shorts DC_IN when batt is connected.

[george-a]

Hi guys,


This one works normally without the battery and also works normally when the battery is connected. BUT when the battery is connected and you plugin the magsafe the green light trembles and switches off. You must remove the magsafe from the AC outlet to start it again because it has detected a short.

I tried all the usual suspects to no avail.


a) U7000 was replaced.

b) All surrounding resistors were measured OK => IMPORTANT NOTE: R7015 was measuring 55K in-circuit (instead of 220K) but was the SAME ALSO OFF-CIRCUIT. So I placed a new 220K in its place and now it is measuring 220K IN-CIRCUIT (this was a question of another user in another topic and Louis said its because the resistor is in-circuit but probably this one is measuring right)! nothing changed.

c) Q7055 was found to be "always open" or shorted between S & D and was replaced. nothing changed.

d) Q7080 & Q7085 were also replaced incase there were not driven properly by their Gates.

e) new battery and original 85W magsafe used.


At this point I could use some insight from the gurus.

br,
george

 

[dukefawks]

PPBUS voltage?

 

[george-a]

with magsafe only: 16.4 to 16.5V
with battery only: 11.9 to 12.0V measured at F7040

 

[jadao]

Are you sure ppbus is 16.5v with magsafe only?
If so PPBUS seems shorted to ppdcin.
Problem with ISL/ transistor buck converter not stepping down or anything between ppdcin and ppbus.
Try replacing ISL and mosfets all at once just in case.

 

[george-a]

PPDCIN at F6905 is 16.8V, then PPBUS_G3H is 16.4-16.6V at F7040. What do you mean?

 

[jadao]

I mean with magsafe only PPBUS_G3H is too high, it should be 12,6V not 16.4-16.6V. The only rail around 16V-17V is PPDCIN.
Whats is resistance between F6905 and F7040? Between Pins 1 and 5 at Q7030?

 

[george-a]

of course you are right PPBUS_G3H is ridiculous at 16.6V!.. Q7030 seems shorted between 1-5. will replace that and report.

 

[george-a]

thats what happens when you miss the basics.. thank you dude. problem solved. note that I missed two things. one the ppbus_g3h correct value and also the short at Q7030 which I measured. need a holiday.

 

[jadao]

Glad you fixed it. What was tricky I think in your case, is that the board worked with ppdcin on ppbus_g3h. Usually when the fan spins we don't give a shit about PPBUS_G3H
So I learned that a board at least 820-2850 could work with PPDCIN shorted to PPBUS without battery.
Hope your battery and sense resistors are still ok.

 

[george-a]

yes and I think that is the reason I oversaw the PPBUS_G3H value - my brain played a dirty game on me. Everything is great so far. thank you again buddy.