LTC1040CN Macintosh Portable

[bibilit]

One of the Portable i have at home is pretty unreliable.

Even with new caps around, was unable to boot properly.

Cleaning and reflowing the hybrid has improved things a bit, most of the time i can boot the Portable, sound is present and everything seems to work properly, but from time to time the Portable will turn itself off and i am unable to make it boot again without struggling.

I can be wrong but i think maybe the LTC1040CN is bad and responsible for this kind of behaviour.

Anyone here has replaced this part for the same reasons ?

 

[techknight]

I would start taking a look at the PMU IC. it will go bad and do weird shit like this. I have had to change a few from parts boards. 

the LTC1040CN is a window comparator and its main job is to tell the system whether the battery is charging and on AC power, or the battery is discharging. As well as make sure the batteries voltage level is above the lockout. once it falls below, on the next latch pulse the LTC1040CN will shut off all regulation until the battery level comes up again.

That IC is a sample-and-hold type, and has an RC Oscillator. sometimes that oscillator will stop running and the machine will permanently lock out unless you "play" with the power by disconnecting and reconnecting all power sources. The other dead giveaway is if the system is saying it is charging when there is no AC adapter connected, or if the AC adapter is connected, battery is low, but its NOT indicating that its charging. 

Also if the system thinks its charging, but it is NOT, the PMU IC will adjust its ADC range to compensate for the voltage difference. So if the battery is at 6V and the system thinks its charging but there is NO AC adapter connect, it will trip the PMU into battery dead condition and shut off as that voltage falls out of range of the battery meter ADC as its not seeing the charging voltage... 

Look for all these. 

IF you see this, a temp fix is to put a 1 meg ohm resistor between 16 and 14 of the IC. this may fix it. 

 

[bibilit]

Thanks for all this information.

The PMU Ic is located on the Hybrid as well ?

 

[techknight]

No, the PMU IC is on the complete other side of the board. next to the VIA. 

 

[bibilit]

ok, thanks, checked yesterday evening the one named PMGR IIRC ?

This is the one i can perform the resistor mod on it ?

 

[techknight]

You will have to try it. It depends on the symptoms as I explained.