Dell Latitude 7420 - Status LED blinks white once

[ongobongo]

Hi Guys
I have a Dell Latitude 7420 here which doesn't want to boot.
If i plug in a charger, the status LED blinks white once only, nothing more, no amber blinks.
I'm trying to start it without battery as the old one inflated and had to come out.
I've tried all kinds of startmethod, holding D, holding CRTL+ESC, holding M+power, nothing works. I've even checked voltage/current consumption: charger changes to 20V and 0,07A but despite the one white blink, nothing else happens.
Does someone have an idea what i should look at / check?
Thanks
ongobongo

[mon2]

Check the DCin mosfet linked to the charger IC. Carefully measure the voltage to ground on each pin of mosfet # PQ41. Post each measurement.

Interested in the source (1-2-3) voltage to ground. Gate (4) voltage to ground. Drain (5-6-7-8) voltage to ground.

[Bill F]

Does the keyboard, power button or caps lock light up? Signs of life. The one white blink is normal when AC is applied. It is a system check to see if the bios is set for wake on AC.

This model has no bios battery. Relies on main battery reserves. It uses an ISL9538 charging IC with dual mosfets. Often the board won't start without a battery. If it does, the bios is reset each time it boots with no battery. It's a very long time before you see a splash and restart. ~2 mins.

You can find rail voltage on PC715, just above the audio ribbon connector. The dual mosfets there are PQ700 and PQ701 driving coil PL701. With no battery the voltage at PC715 will be about 8.5v.

[ongobongo]

Thanks for thee swift feedback guys.
bill I checked PC715 and I indeed have 8,6v there with the charger attached. And i don't have any additional light, neither power button nor caps lock light up.
I also tried to start it with keeping the charger on for longer, as you suggested. Unfortunately, no success. As I#m not sure if the laptop even starts without a battery, I'll take small steps and get a working battery first. Maybe that will already fix the issue.
I'll come back once i have a battery and know some more details.
Thanks so far
ongo

[ongobongo]

A quick status update:
The fix was easier than expected, a new battery did the trick, laptop is booting and working fine.
Thanks for the support on this one.
see ya
ongo