Where voltage is coming from - Aspire Aspire 3

[Jane]

Aspire Aspire 3 - model is A315-41-R71G - does not start.There are not +3VALW and +5VALW . They are generated by PU401
RT6575DGQW - see enclosed picture .
Can you please let me know where 3V_EN for EN2 and 5V_EN for EN1 are comming from ? 3V_EN is only 2,6V and 5V_EN is only 3.27V
(Also FB1 and FB2 are only about 0.4V)
Thank you for advice

[mon2]

See the bottom left side of your posted schematic. Label EC_ON. This voltage is high enough to enable the local +5ALW rail. Remove all power. Meter in resistance mode. Measure the resistance to ground of this +5ALW rail. What is the resistance?

Repeat for the +3ALW rail.

[Jane]

Thank you for your reply.
I measured:
0,242 is for +3VALW and 0,494 for +5VALW
Are they OK?

[mcplslg123]

Enable for 3V/5V comes from SIO. If the readings in post #3 is in diode mode then the reading seems fine.However,its better to measure in resistance mode(200K scale)

[mon2]

Post a clear pic of the meter face for one of these checks so we can confirm the scale used for the measurements.

[Jane]

Here it is

[mon2]

So your measurements are for the diode mode. The units of the measurement are in volts and is the voltage drop across the internal diode of the part. If the voltage drop is too low then the part is considered to be shorted.

so the reading is 0.496 volts for this check. A typical good diode will be 0.6 volts. Both of these checks are ok.

Next, switch to dc voltage scale on your meter. Measure the voltage to ground of these ldo rails (not the enable pins). Post each measurement.

if the enables are ok and the output ldo rails are not yet the ldo rails are not shorted like in your case, then this usually means this regulator is defective and will need to be replaced.

what is the voltage to ground of pin #3 ?

pin #13 ?

[Jane]

LDO3 ( pin#3) is about 3.27V, LDO5 (pin#13) is about 5.1V.
I think these should be OK, yet 3VALW and +5VALW not good.
What should I try next?
Thank you for a hint,

[mcplslg123]

Replace the tantalum caps connected with both 3V/5V coils with smd cap of 330uF.

[прямо]

The regulator needs BOTH 5V_EN and 3V_EN to start switching. Because these signals are lower than they should be, the IC doesn't switch, hence no PWM output, both FB pins are low, and I bet PGOOD is also low.

You said these enable signals are generated by the IC itself? Are you sure?

Somehow I DON'T THINK SO. No direct connection from the IC LDO3 and LDO5 to its enable pins in the schematic, BUT it indicates CLEARLY that 5V_EN comes from external sources EC_ON and MAINPWON, not 5VLP.

So make sure of that. Find where 3V_EN is coming from using the search function of your PDF reader.

Next step is, you need to measure the points at EC_ON, before and after the 2K2 resistor. If before the resistor you get 5V but after the resistor you get a lot less than that, then the resistor needs to be replaced.

Do the same measurement with MAINPWON if there is a 0 ohm resistor instead of a direct connection.

Repeat for 3V_EN.

[Jane]

Thank you for replies
@прямо:

You said these enable signals are generated by the IC itself?

No,I found out that enable signals are coming from KB9022Q D (ENE), I think it is SIO chip.

EC_ON is 3.29V both before and behind the PR413 (2K2 resistor).
3V_EN is 2,6V and comes from that KB9022Q D (ENE) too.
Does it mean KB9022Q D (ENE) is faulty?

[mcplslg123]

Replace the tantalum caps connected with both 3V/5V coils with smd cap of 330uF.

Did you act on this suggestion?

[прямо]

Thank you for replies
@прямо:

No,I found out that enable signals are coming from KB9022Q D (ENE), I think it is SIO chip.

EC_ON is 3.29V both before and behind the PR413 (2K2 resistor).
3V_EN is 2,6V and comes from that KB9022Q D (ENE) too.
Does it mean KB9022Q D (ENE) is faulty?

No. RT6575D enable signals must be higher than 1.6V for it to start switching.

You can either replace RT6575D or do what mcplslg123 suggested, though I have no idea which 5V/3V coils he/she is referring to.

[Jane]

RT6575D was already replaced in the past.
But now I split Pj403, pj404 .
No voltages appeared but after connecting PJ404 together , 5VAWL voltage appeared .
But there is still no 3VAWL
@mcplslg123 Can you please explain in further details? What coils / cappacitors to replace?

[mcplslg123]

PC413/414-replace them with 330uF smd capacitor.