Trying to diagnose fault on dell LA-9104P board

[NickyD-]

this board does turn on at all, no light nothing.
I'm finding that the gates of PQ114 are not being turned on, has no voltage on the pins.
so i then went to measure voltages of PU100 and found
pin 22 dcin: 19.27 volts
pin 13 acok: 0 volts
pin 2 acin: 2.62 volts, which i see it needs to be 3.2+ to turn on pin 13 ACOK
pin 26 vcc: 4.85 volts
pin 21 vddp: 3.86 volts

little lost where to go now

[NickyD-]

Re: Trying to diagnose fault on dell LA-9104P board

here is a pic of schematic im referencing

[budm]

Re: Trying to diagnose fault on dell LA-9104P board

What Voltage do you have at P2 and ACOFF?

[NickyD-]

Re: Trying to diagnose fault on dell LA-9104P board

What Voltage do you have at P2 and ACOFF?

I measures p2 at the source side of Mosfets pq100 and pq101 both 19volts.
I measured Acoff and pin 27 of the kb9012qf chip and got no voltage. I also checked all pins labeled vcc of that chip and didn't find any voltage either

[emestee]

Re: Trying to diagnose fault on dell LA-9104P board

which i see it needs to be 3.2+ to turn on pin 13 ACOK

Check the voltage divider that feeds it.

[NickyD-]

Re: Trying to diagnose fault on dell LA-9104P board

Check the voltage divider that feeds it.

I'm sorry. But check which one

[emestee]

Re: Trying to diagnose fault on dell LA-9104P board

I'm sorry. But check which one

Look at the schematics (and the charger IC datasheet). As you yourself said, the IC won't let ACOK go up if ACIN is too low, and it is. The voltage on ACIN is formed by a voltage divider right next to it. If the voltage is really too low, then either one of the resistors in the divider drifted away from nominal, thus skewing ACIN downwards, or the input voltage to the divider is too low. In this configuration (50k/25k divider) you should be seeing about 6V on ACIN. If PR142 changed its nominal to about 150K, you'd be seeing 2.6V on ACIN.

[NickyD-]

Re: Trying to diagnose fault on dell LA-9104P board

So resistor 1 of the divider measured 160k, schematic showed 232k, and resistor 1 did show 19.55volts on vin side.

Resistor 2 measured 46k and in schematic showed 49.9k

But with those resistance values I would of expected the voltage to be be 4.36 volts instead of 2.62...

[budm]

Re: Trying to diagnose fault on dell LA-9104P board

Post # 1: I'm finding that the gates of PQ114 are not being turned on, has no voltage on the pins.
Post #4: I measured Acoff and pin 27 of the kb9012qf chip and got no voltage.
Since ACOFF (drives the Base of PQ109) is 0V, that means PQ109 (NPN) is not turned on so Collector (1) which is connected to Gate of PQ114 should be high but you are getting 0V as reported in post #1, and the Collector of PQ109 is connected to the resistor PR139 which one end is connected to ACN (ACIN) which you report to have 2.62V. So to have Gate of PQ114 to be at 0V, it is either PQ109 is shorted between Emitter and Collector, or the Collector resistor is open, or Gate is shorted to GND.
BTW, ACIN has TWO pull-up resistors (for two Voltage sources) PR 112, PR137 so if any one of those two resistors goes to ground (one end of the resistor connected to Logic output) the it will affect ACVIN Voltage level.