dell latitude 7490 la-f322p no power

[kjchatman]

this board does not seem to have a short to ground. 19 volts gets to the current sensing resistor. 12 volts is on the battery terminal. there is 0v on the battery smbus but i don't have a battery for it and that might be the issue. will someone tell me whether this board needs a battery installed to power up?

[mcplslg123]

Re: dell latitude 7490 la-f322p no power

Nope. All laptop mb will work in ac adapter mode(without battery).So to powerup, battery is not needed.Btw, if you have 0 volts on smbus that indicates perhaps absence of 3v LDO. So do check your 3V PWM regulator's requirements and measure the resistance on 3V LDO.

[kjchatman]

Re: dell latitude 7490 la-f322p no power

gettin 0v on 3v5v_en with comes from alwon. what is alwon

[mcplslg123]

Re: dell latitude 7490 la-f322p no power

ALWON=Always On. This signal comes from SIO and is needed to get output on 3/5V coils. But first you need to get 3V LDO. The PWM regulator will generate it without ENABLE signal.

What is the voltage and resistance on 3V LDO??

[kjchatman]

Re: dell latitude 7490 la-f322p no power

the sio which is a bga package appears to the issue. rtc_cell has a short to ground and i ran 1v through its path and the EC lit up like a christmas tree on the thermal camera. i would reball it but i'll assume that it's dead since i reflowed it real good and nothing changed. the chip is mec5105

[kjchatman]

Re: dell latitude 7490 la-f322p no power

is reprogramming easy enough? i know how to reprogram a bios

[mcplslg123]

Re: dell latitude 7490 la-f322p no power

A shorted ec needs to be replaaced , not reballed. Its bit difficult to program these bga ec.

[kjchatman]

Re: dell latitude 7490 la-f322p no power

well i replaced the sio with a new one and the short on +rtc_cell is back. is measures 1.1 ohm resistance to ground

[tom081081]

Re: dell latitude 7490 la-f322p no power

well i replaced the sio with a new one and the short on +rtc_cell is back. is measures 1.1 ohm resistance to ground

Hi kjatchman,
I have exactly the same issue - +RTC_CELL shorted to the ground (~1 Ohm) and no ALWON signal. I haven't done a short-circuit test yet because I don't have a thermal camera, I need to borrow.
Have you solved this problem on your laptop?
I would appreciate any advice

[mcplslg123]

Re: dell latitude 7490 la-f322p no power

Short on RTC is usually related to shortedRTC section of PCH . Trace this signal to PCH and check resistance there. If you are lucky,it can be a shorted cap on the backside of SOC but very unlikely.