T42 shows it's on battery when AC adapter plugged in

[madrigal]

Hi,
Recently I obtained used T42 with notorious GPU problem. After successful reflowing it turns out that there are some other problems:
1. Battery was not charged.
2. Even though the AC adapter was plugged BatteryMaximizer program stated that laptop runs on battery.

After some research the problem No 1 was solved (thanks to the AdaSch and these topics http://forum.thinkpads.com/viewtopic.php?f=2&t=82741 http://forums.thinkpads.com/viewtopic.php?f=2&t=70832)

Now battery is charged well but BatteryMaxiMizer continues to show that laptop works on battery when AC is conected. Even when battery is charging (charging percentage constantly goes up), in BatteryMaxiMizer applet status of the battery is "Discharging", which is strange. In addition to that from time to time laptop produces the known beep suggesting that AC adapter is plugged/unplugged even though adapter is firmly plugged in.
I think that somewhere on the motherboard should have switch (transistor or etc.) which gives the signal to the software that AC adapter is plugged in. If this switch is blown, software will show that laptop is running only on battery.
If someone have ah idea what is going on, please, let me know. I have a donor motherboard and it won't be a problem to replace a defective part.

P.S. Recently I obtained some IBM's schematics - if anyone need such information, PM me and I will send you the file.

[SMA]

Sounds to me like you have done re-work on the ADP3806 and got something wrong around pin 2, 3 or 4

[madrigal]

Sounds to me like you have done re-work on the ADP3806 and got something wrong around pin 2, 3 or 4

Yes, ADP3806 was replaced and charging the battery is OK now.
I don't think that problem is connected with ADP3806 replacement because it was done by good skilled professional and aside that even before replacing ADP3806 and 8023 MOSFETs BatteryMaxiMizer showed that laptop works always on battery and the beeps signalizing for plugged/unplugged AC adapter occurred at random.
OTOH if you are sure that differential amplifier AMP2 from ADP3806 is used to monitor presence of AC power I'll investigate the chains around the pins 2,3 and 4 even though according to schematics I have it's not so obvious.

[SMA]

The output of the mentioned op-amp ends up on the TB62501F pin 2, where you can measure it.
I beleive that, 0 V on TB62501F pin 2 means that current is being drawn from the AC Adapter and 3.3 V means that no current is being drawn from the AC Adapter.

[madrigal]

Hi,
Is it possible to have additional elements between pin 4 of ADP3806 and pin 2 of TB62501F?
I have some schematics (I'm not sure they are for IBM T42) on which ADP3806 pin 4 generate EXTPWR signal via diode and MOSFET. Tomorrow I'll try to localize them and to measure some voltages.