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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!
Joe
Posted 2013-02-22T18:42:34.610
Reputation: 340
The circuit itself could have been damaged. In most charging circuits there is a diode that will allow the excess voltage to go to ground or shunt when the charge is complete. This diode could be damaged. – Pow-Ian – 2013-02-22T20:35:04.800
Interesting. If that was the case couldn't I test for voltage passed the suspected diode, which would yield no current.. right? – Joe – 2013-02-22T21:06:13.597
I would assume yes you could however who knows where the diode is, or if it is even a diode. They could have used another switching mechanism all together. Are you able to get it to power on without the battery installed? – Pow-Ian – 2013-02-22T21:17:07.820
No. Battery only, unfortunately. – Joe – 2013-02-22T21:23:48.730
So the power is getting to the board from the battery and not from the adapter. This defiantly sounds like the charging circuit got yacked. Obviously there is a switching circuit that allows voltage from the battery or from the plug to run the machine. It would seem this circuit is damaged because it is not letting voltage from the adapter into the board. You may need a new mother board unless the charging board is not integrated, sometimes they are separate. – Pow-Ian – 2013-02-22T21:26:11.213
Unfortunately they are not separate and your prognosis was exactly what I thought and feared :/
What confirms this further... the dc jack itself has a little indicator light which is on when there is power from the ac adapter, regardless if the laptop is on - which also does not function normally. My assumption is that this light is powered by the same switch mechanism we fear is yacked. Sound about right? – Joe – 2013-02-22T21:29:58.257
Yeah the indicator would be inline with the voltage and that LED would defiantly be powered by the same circuit. – Pow-Ian – 2013-02-22T21:32:21.193
In other words - if this 'switch' was set to 'on' it would return power to the dc jack to illuminate the light. – Joe – 2013-02-22T21:32:55.680
Cool. Just wanted to check with a second brain. :) Thanks for your time, Pow-lan. – Joe – 2013-02-22T21:33:50.513
I know how that can go. Good luck. – Pow-Ian – 2013-02-22T21:38:59.223