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View Full Version : G73SW Meltdown / Smoke with pics.



BrettRGM
09-17-2014, 08:53 AM
Anyone want to take a guess at what happened here? My old battery died and my oem power supply was getting kind of ghetto, so I got a new battery (The one from Dr. Battery for the G73) and a new power supply (A PWR+ AS9).

Turned it on, and it smelt like smoke, the front leds were going nuts. I turned it off, tested the power supply (it was putting out 19v like it should have been), took the battery out (it smelled like it was coming from back there) and it ran on AC power. I put the battery back in and it showed no battery detected, but if I pulled the plug it ran (only tested for a few mins).

So, I took it apart and found this meltdown near the battery circutry.

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So, I got a new motherboard, used the same battery that I had in it when it fried with my old AC adapter (also still putting out spec 19v), and it's working absolutely fine, charging, etc.

So what do you guys think happened there? I haven't had the balls to try out the new AC adapter on the working motherboard with the same battery, but I tested it with a multimeter so it seems like an unlikely culprit...?

Anyway, that was weird, just looking for some theories.

Sci-ops
09-25-2014, 11:11 AM
That is quite a bit that you had gone through. My sympathies. I will speculate although I am no expert. I once repaired my old M51sn motherboard on my own which I shorted. I didn't know what or where the problem was so I had to go through all the schematic and became a little familiar with how laptop motherboards work.

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This is interesting. On my G73sw board the IC reads MB39A132. This is a Lithium battery charger IC.

The inductor nearby looks damaged too. I know coils can produce can produce a high voltage in the form of back emf so I thought that was interesting.

The burning on the pins on the IC looks like pin 27 to me which is "out2" . I am no expert but I think this pin goes out to trigger the charred mosfets on the other side board.


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The MB39A132, which is used for charging Li-ion battery, is a synchronous rectification DC/DC converter IC adopting pulse width modification (PWM). It can control charge voltage and charge current separately and supports the N-ch MOS driver. In addition, the MB39A132 is suitable for down-conversion. The MB39A132 has an AC adapter detection comparator, which is independent of the DC/DC converter control block, and can control the source supplying voltage to the system. The MB39A132 supports a wide input voltage range, enables low current consumption in standby mode, and can control the charge voltage and charge current with high precision, which is perfect for the built-in Li-ion battery charger used in devices such as notebook PC. It is used in built-in chargers for notebook PCs, handy terminals, etc.
Parametrics

MB39A132 absolute maximum ratings: (1)Power supply voltage, VVCC VCC pin: -0.3 + 27 V; VVIN VIN pin: -0.3 to + 27 V; (2)CB pin input voltage VCB CB pin: -0.3 to + 32 V; (3)CTL1, CTL2 pin input voltage VCTL CTL1, CTL2 pins: -0.3 to + 27 V; (4)Input voltage VINC -INC1, +INC1 pins: -0.3 to + 27 V; -INC2, +INC2, BATT pins: -0.3 + 20 V; VADJ ADJ1, ADJ2, ADJ3, CELLS pins: -0.3 to VVREF + 0.3 V; VINE -INE1, -INE3 pins: -0.3 to VVREF + 0.3 V; (5)ACIN input voltage VACIN ACIN pin: -0.3 to VVIN V; (6)ACOK pin output voltage VACOK ACOK pin: -0.3 + 27 V; (7)Output current IOUT OUT1, OUT2 pins: -60 to + 60 mA; (8)Storage temperature TSTG: -55 to + 125 ℃.
Features

MB39A132 features: (1)Supports 2/3/4-Cell battery pack; (2)Two built-in constant current control loops; (3)Built-in AC adapter detection function (ACOK pin); (4)Charge voltage setting accuracy: 0.5%; (5)Charge current control setting can be selected without using any external resistor. (RS = 20 m 2.85 A); Charge current can also be freely set by using the external resistor; (6)Switching frequency can be set by using the external resistor(MB39A132 has a built-in frequency setting capacitor.):100 kHz to 2 MHz; (7)Built-in off time control function; (8)In standby mode (Icc = 6μA Typ), only the AC adapter detection function is in operation; (9)Built-in output stage for N-ch MOS FET synchronous rectification; (10)Built-in charge stop function at low VCC pin voltage; (11)Built-in soft-start function whose setting time can be adjusted; (12)Equipped with the function enabling the independent operation of the AC adapter current detection amplifier; (13)Package: QFN-32.


On the other side of the board the 2 mosfets look like they are connected in series? This looks like the ground zero of the event. My theory would be that these mosfets took too much and shorted. Then it burned it's way to the MB39a132 on the out pin. Since those mosfets should be connected to the 19V system, which is for high voltage things like charging battery, running LCD backlight inverters...I think it must be something to do with the adapter which is supposed to provide 19.7V and 8A max . One problem though is I wonder why the fuse near the adapter port hasn't blown instead. Did you check that fuse?
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