Meter the 5V rail feeding the system, while adjusting your input voltage. A variable DC Bench supply would be preferable here.
that 5V rail should be a rock solid 5.2VDC even down to 6.3V input voltage. If it is not, then something is wrong with the Hybrid, or the MOSFET itself is bad. it is a P-Channel mosfet.
the LTC1040 forms a window comparator, that when the input voltage drops below 5.9V, it will lock out the 5V regulator so it falls to 0v. The other side of the comparator is used to tell the system whether the battery is in a charge state, or a discharge state. the window comparator senses the AC adapter voltage versus the battery voltage via a sense resistor, and will latch on the next oscillator pulse (internal to the LTC1040CN), and switch on the charging circuit. or not.
There is a small 8pin op-amp in the top left corner of the hybrid, its responsible for regulating the 5V rail. its error output feeds the MOSFET itself. if the MOSFET is bad, and the R(ds) is too high, it wont bring the voltage up high enough. Likewise if there is something bad on the hybrid, the same thing happens.
From my experience, the hybrids that exhibits the most problems are the ones that look "discolored" from tons of cap goo getting into the ceramic substrate. The most common thing is, the Goo changes the cross-conduction between traces, and creates parasitic resistors that screw things up. This cannot be fixed for the most part, However, the closest thing to the caps is the resistor/capacitor network that forms the latching oscillator for the LTC1040. When the oscillator does not run, it will cause the portable to have random no-power at all symptoms, or no-charging indicator.
Anywhere from 1Meg to 100K I have been able to get the oscillator started again. But if the damage is extensive, it may have affected other circuits as well.
The only fix is to reverse-engineer the Hybrid and create a new PCB with equivalent parts.
that 5V rail should be a rock solid 5.2VDC even down to 6.3V input voltage. If it is not, then something is wrong with the Hybrid, or the MOSFET itself is bad. it is a P-Channel mosfet.
the LTC1040 forms a window comparator, that when the input voltage drops below 5.9V, it will lock out the 5V regulator so it falls to 0v. The other side of the comparator is used to tell the system whether the battery is in a charge state, or a discharge state. the window comparator senses the AC adapter voltage versus the battery voltage via a sense resistor, and will latch on the next oscillator pulse (internal to the LTC1040CN), and switch on the charging circuit. or not.
There is a small 8pin op-amp in the top left corner of the hybrid, its responsible for regulating the 5V rail. its error output feeds the MOSFET itself. if the MOSFET is bad, and the R(ds) is too high, it wont bring the voltage up high enough. Likewise if there is something bad on the hybrid, the same thing happens.
From my experience, the hybrids that exhibits the most problems are the ones that look "discolored" from tons of cap goo getting into the ceramic substrate. The most common thing is, the Goo changes the cross-conduction between traces, and creates parasitic resistors that screw things up. This cannot be fixed for the most part, However, the closest thing to the caps is the resistor/capacitor network that forms the latching oscillator for the LTC1040. When the oscillator does not run, it will cause the portable to have random no-power at all symptoms, or no-charging indicator.
Anywhere from 1Meg to 100K I have been able to get the oscillator started again. But if the damage is extensive, it may have affected other circuits as well.
The only fix is to reverse-engineer the Hybrid and create a new PCB with equivalent parts.