I'm a computer technician, so please avoid the obvious diagnostic suggestions - info provided.
I'm working on a Compaq Presario CQ40. Originally, the battery would not charge or run off ac adapter. Tested battery - good. Tested AC adapter - good. Tested dc jack with questionable results - decided to replace with no avail.
I went back and replaced the battery/ac adapter with known good. Tested new dc jack with multimeter - continuity confirmed, voltage confirmed. I even tested the motherboard solder joints for voltage - everything checked out fine!
What the heck could possibly be causing this? I've fixed thousands of laptops and never seen anything like this.
Please help! Thanks so much!