FX505DT No power

[tommy97]

Hi, I have problem with ASUS FX505DT, it was brought to me for no power, instant short on U8100 (TPS51225C), I've got replacement chip, nothing been changed (Chip warm up instantly after connecting the charger for up to 80C).I believe that +VDDCR_CPU_SOC or just low resistance 4ohm, (L8002 6.5Ohm to the ground, L8001 4.5Ohm to the ground, L8000 4.5Ohm to the ground), any advice what i should look for?

[mon2]

This low resistance is ok for a cpu / gpu. Start with checking the usual dcin mosfets. Do review the sticky above on charger circuits by piernov.

measure the voltage to ground of each mosfet pin.

source (1-2-3)
gate (4)
drain (5-6-7-8)

post each measurement. Also share the topside markings of these dcin mosfets and the charger ic. post pics of the area if not known.

[piernov]

No resistance to ground measurements on 3V/5V regulator?

[mcplslg123]

If U8100 is heating up,then very likely one of the LDO rail is shorted.Measure resistance to GND on 3V LDO and 5V LDO. No power attached.

[tommy97]

Q8801&Q8802 - Gate 24V, Source & drain 19V (SM4511 Both) mon2
5V_LX 0.24v 3V_LX Missing, 5VA Missing, 3VA &+RTC POWER Missing
Q8100 - Drain and source 19V - Gate missing

U8100 Resistance to the GND: piernov , mcplslg123
1:180K
2.9K
3.5Ohm
4..1oh
5.0.7ohm
6.10k
7.100k
8.5k
9.2Mohm
10.128k
11..135k
12.1.2ohm
13.414k
14. 15k
15.137k
16.145k
17. ol
18.15k
19.3.3Ohm
20.10k
.

[mcplslg123]

Pin3 is for VREG3 aka 3V LDO and is clearly shorted to GND. You need to inject voltage(1V/5A) and see if anything is getting hot. Very very likely your SIO is shorted.

[tommy97]

mcplslg123 you were right, short lead to KBC (IT8987e), i've replaced it (spare from the old board), laptop power up/charge battery, however it does not display, keyboard backlight is on, react for pwr button, sometimes HDD light flash once, sometimes restarting. mon2?

It draw 0.55amp without battery and 2.4amp with the battery attached.

[mon2]

What are the voltage to ground readings for the charger IC @ U8800A for:

ACOK
ACDRV
ACDET

[tommy97]

ACDRV - 24.5v
ACDET 2.65v
ACOK - 3.1V (5th leg)
mon2

[mon2]

These are good measurements to enable the DCin mosfets (Q8801 / Q8802).

Confirm the voltage to ground of the DCin mosfets @ Q8801 and Q8802. Is the voltage stable @ drain pins 5-6-7-8 of Q8802?

[tommy97]

Everything look in order 19.5v on Source and Drain, Gate 24.5v, i've just checked how it does power without the LCD connected and it seem to work, it goes to 1.2amp with no battery cpu & gpu gets hot, does not restart, fan spin. Where when connected LCD laptop goes to 0.50amp and restarting 3-6 times and then standby on 0.50amp no fan spin, checked on known tested lcd, same problem.
mon2

[mcplslg123]

IT8987E is programmable SIO.Since you got the SIO from another board,the EC firmware wont match. You need to program this SIO first with a SIO programmer like SVOD etc.
However, if you dont own a SIO programmer,then order a new blank SIO and solder it.It'll flash itself on first boot.

[tommy97]

mcplslg123 thanks for your answer, I was thinking that it might be the case... I'll keep the post updated when I get the part.

[G. Sling]

Hello,
Which boardview file did you use for FX505DT. Looked around cant seem to find one.