LENOVO DG425/DG525/DG725 NM-B321 NO POWER

[madjid911]

hello, I have a Lenovo that does not turn on at all, I flashed the bios but no result, the battery charges well I have 3v and 5v, the sio chip is well powered, taking all the voltages I noticed that the bios was not powered even after pressing the keyboard power button.

I'm missing +1.8VS, but I have +3VALW_APU and +1.8VALW.

Can you explain to me how to analyze the attached diagram to get +1.8VS please, thanks

SCHEMA AND BRD : https://www.badcaps.net/forum/troubl...st#post1770089

[mon2]

For me, it is easier to start the review with the mosfet in question which for your case, it is Q39. Start with measuring the voltage to ground of each pin cluster.

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

You have noted, that the voltage does not reach the pins 1-2-3. By reviewing the datasheet for this mosfet, we know it is a N-channel mosfet. For this mosfet to enable, the gate voltage (pin # 4) must be higher than the voltage being passed between source / drain pins. Measure the voltage to ground of pin # 4.

Review the schematic to confirm the power path from V20B+ (right side of the partial schematic) -> to the gate pin # 4 of this Q39 mosfet. If the voltage is not higher than 1v8 at the gate pin, then someone is pulling this trigger voltage down or there is a break in the PCB traces and/or components in this same power path.

[madjid911]

For me, it is easier to start the review with the mosfet in question which for your case, it is Q39. Start with measuring the voltage to ground of each pin cluster.

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

You have noted, that the voltage does not reach the pins 1-2-3. By reviewing the datasheet for this mosfet, we know it is a N-channel mosfet. For this mosfet to enable, the gate voltage (pin # 4) must be higher than the voltage being passed between source / drain pins. Measure the voltage to ground of pin # 4.

Review the schematic to confirm the power path from V20B+ (right side of the partial schematic) -> to the gate pin # 4 of this Q39 mosfet. If the voltage is not higher than 1v8 at the gate pin, then someone is pulling this trigger voltage down or there is a break in the PCB traces and/or components in this same power path.

Thanks for your help

source (1-2-3) : 0V and 3,3 KOHMS
gate (4) : 0V and 110KOHMS
drain (5-6-7-8) : 1V8 and 9,6 KOHMS
Mode diode : 377/1163

Q45 and Q46 : Pin1 : 0V, pin 2 : 4V7 , pin 3 : 0V

I don't have V20B+, so I looked at the R214 resistor : pin 1 : 0V (no short), pin 2 : 20V. I have a lot of macbook air a1466 donor motherboard, I found a resistor of 300K, in the diagram r214 is at 270K, can I replace it with a 300K? I didn't find 270K

[mon2]

Can you confirm that V20B+ is missing since +3VALW_APU is also based on the same power rail source. You have +3VALW_APU? Best to measure for the presence of V20B+ at the DCin mosfets -> check pins 5-6-7-8 (any of these are ok) on mosfet PQ202.

[madjid911]

Can you confirm that V20B+ is missing since +3VALW_APU is also based on the same power rail source. You have +3VALW_APU? Best to measure for the presence of V20B+ at the DCin mosfets -> check pins 5-6-7-8 (any of these are ok) on mosfet PQ202.

Yes +3VALW_APU 3V4, V20B+ is present 20V5 but not on the mosfets, only on R214 pin 2, but pin 1 0v. so I thought it was the resistor that was dead, but when unsoldering it I lost it, I replaced it with a 300 Kohms but the result is the same I have 20V5 on pin 2 but 0v on pin 1

[mcplslg123]

Check Resistance to GND on R214,pin1.

[madjid911]

Check Resistance to GND on R214,pin1.

Sorry, I meant Pin 1 : 20V5 and 161 OHMS. Pin 2 : 0V and 197OMH. (on the diagram they reversed R214 PIN 1 AND 2).

I changed the resistance, I don't understand why I can't get 1V8VSGATE, I don't have any shorts on it

[mcplslg123]

I doubt your measurements. Just confirm what is the voltage on pin 4 of Q39 ? If R214,pin1 has indeed 20V,then Q39 ,pin4 must be 20V also.However, without any voltage on pin2 of R214,i cant imagine voltage on pin1 of R214.

So double check your readings again.

[madjid911]

I doubt your measurements. Just confirm what is the voltage on pin 4 of Q39 ? If R214,pin1 has indeed 20V,then Q39 ,pin4 must be 20V also.However, without any voltage on pin2 of R214,i cant imagine voltage on pin1 of R214.

So double check your readings again.

Q39 Pin 4 : 0V. Pin 5 : 1V8
R214 Pin 1 : 20V5V. Pin 2 : 0VV

pay attention on the schematic the r214 is reversed

[mcplslg123]

Ok, the issue here is with SUSP and SUSP# signal. Q45/Q46 both are N channel,so the gate(pin2) must be low so that R214 allows to pass 20V to Q39 pin4. Trace the SUSP signal and it'll lead you to SUSP#. So trouble shoot within this area.

[madjid911]

Ok, the issue here is with SUSP and SUSP# signal. Q45/Q46 both are N channel,so the gate(pin2) must be low so that R214 allows to pass 20V to Q39 pin4. Trace the SUSP signal and it'll lead you to SUSP#. So trouble shoot within this area.

RE18 pin 1 (+3VL_EC) 3V5; pin 2 (SUSP#) 0V.
SUSP : 4V7
SUSP# : 0V

Is it the sio chip IT8586E that generates the SUSP# ? In this case it would be defective ?

[mcplslg123]

Yes, SUSP# is generated by SIO but it goes to APU. More often then not,SUSP# is not generated 'coz of bad APU/SOC. You need to probe each and every area of SUSP/SUSP# before concluding bad APU.

Right now,you're getting just the opposite values on SUSP/SUSP# lines.Working scenario is SUSP-0V and SUSP#-high.

[madjid911]

Yes, SUSP# is generated by SIO but it goes to APU. More often then not,SUSP# is not generated 'coz of bad APU/SOC. You need to probe each and every area of SUSP/SUSP# before concluding bad APU.

Right now,you're getting just the opposite values on SUSP/SUSP# lines.Working scenario is SUSP-0V and SUSP#-high.

strange I have 0V everywhere on SUSP# and 4V5 everywhere on SUSP, is it necessary to try a new sio? Or should I give up

[mcplslg123]

You need to check all the points where SUSP/SUSP# goes. SIO is very unlikely the culprit. Its either any of the mosfets on SUSp/SUSP# lines or the SOC is dry/bad.What i suggested is based on experience and not measurements since you've not done any troubleshooting.