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A1286 820-3330 Intermittent Green Light No Power

computercaverva

computercaverva

Member
Working on a stack of 820-3330's tonight and I have stumbled across a weird one. I had to replace the ISL as it had blown Q7030 and Q7035 MOSFETs. It came in with no power but occasionally gets a green light. When the light is on or off the PP3V42 is high (3.415 V), SMC_ACOK is 3.25V, I am investigating around U6990 and noticed that P3V42G3H_BOOST seems high to me as on one side of C6994 I have 6.8V and the other side close to the coil as 3.3V. What else should I check for?
P.S. PPBUS_G3H is 1.2V
 
smiba

smiba

New member
SMC_PM_G2_EN high?
Voltage of PP5V1_CHGR_VDD and PP5V1_CHGR_VDDP?
Resistance to ground on PPBUS_G3H in Ohms?
F7040/41 fuses not blown?

P3V42G3H_BOOST being 'too high' is probably just your multimeter getting confused by the switching, if PP3V42 itself is alright then no worries about it.
 
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2informaticos

2informaticos

Administrator
Staff member
P3V42G3H_BOOST MUST be higher.
It is usually aprox 5V higher than the output; check how a buck controller works...
However, it is not a DC voltage only there; as it uses the coil pulses.

=PP3V42_G3H_REG is completely independent of PPBUS_G3H, on AC mode.

Check for corrosion around U6990.
Don't forget R6991/92/95/96.

Assure =PP18V5_DCIN_CONN is stable; if not, means charger detects some leakage on the input of the board..
 
computercaverva

computercaverva

Member
SMC_PM_G2_EN is high, 3.38v.
PP5V1_CHGR_VDD is 5.469
PP5V1_CHGR_VDDP is 5.474
Resistance to ground on PPBUS_G3H is -1.025 fluctuating Mega Ohms. May not be doing this right. Not sure why it would show negative unless I had the probes backwards.
The fuses F7040/41 appear fine.
 
D

dukefawks

Administrator
You are seeing a negative value because either you have power applied or there is residual charge on the rail. Is PPBUS even present and is it 12.56V? Check resistance between pin 17/18 and 27/28 of U7000? DCIN present on U7000?
 
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dukefawks

Administrator
If there is no short on PPBUS then I would say you killed the 6259 or bad soldering. Also I asked DCIN on U7000, not the DCIN charger rail.
 
computercaverva

computercaverva

Member
I'm very sorry, I don't mean to be stupid but from the schematic it sounds like the PPCHGR_DCIN is the DCIN for U7000, but if not I'd definitely like to be corrected. I've replaced the U7000 twice, I'm concerned I may have a bad batch, Thanks a bunch for the help.
 
computercaverva

computercaverva

Member
No trouble, can't thank you guys enough. I'm out of the office at the moment but will be in around 5:00 PM EST. I'll give that a look and let you know.
 
computercaverva

computercaverva

Member
Sorry for the delay, under the weather. The board doesn't power on with the battery plugged in, but with just the power from the battery, I do get 11.8v on pin 24 of U7000. On just the DC jack, I get 2v.
 
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dukefawks

Administrator
Then the issue is not with U7000 as the system would power on without it. Still want to know resistance to GND on PPBUS.
 
computercaverva

computercaverva

Member
Found a bad diode, very hard to see that it was cracked--D6990. Replaced the diode and now getting a green intermittent light on the charger. Checked PPBUS_G3H, I now have a steady 12.28v. With the battery and charger plugged in, I get a steady green light, not orange. Jumped the power on pads to be sure the system won't turn on, no fan spin.
 
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dukefawks

Administrator
PPBUS voltage without battery? If 12.23 and the battery indicator also not working I will still say bad SMC.
 
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