Dell laptop model PP24L won't start from ac adapter

[mon2]

Re: Dell laptop model PP24L won't start from ac adapter

while black probe to ground and red probe on any pin of CLR, i got reading of "1" infinity.

This is a good reading and means that the 200 ohm scale is too low to measure this resistance to ground. Specifically, you will then need to switch to the higher scale till you can get a true reading. If you see a '1', switch to a higher scale.

This also confirm that there is no shorted parts on this power rail. If there is a short on the rail, the power supply will sense this and shut down the power.

If you wish to measure the resistance of the actual current sense resistor, measure with the probes across the component while in 200 ohm scale.

[mikey5791]

Re: Dell laptop model PP24L won't start from ac adapter

This is a good reading and means that the 200 ohm scale is too low to measure this resistance to ground. Specifically, you will then need to switch to the higher scale till you can get a true reading. If you see a '1', switch to a higher scale.

This also confirm that there is no shorted parts on this power rail. If there is a short on the rail, the power supply will sense this and shut down the power.

If you wish to measure the resistance of the actual current sense resistor, measure with the probes across the component while in 200 ohm scale.

On measuring resistance to ground, i put my dmm black probe to ground screw nearby and my red probe to either end of the resistor. 200 ohm scale , 2k, 20k scale still shows '1'. The final reading is 5.8k on 200k ohm scale.

When i measured with probes across the resistor while in 200 ohm scale , i got reading of 0.5 ohm.

[mikey5791]

Re: Dell laptop model PP24L won't start from ac adapter

Hi,
Sorry to say i have no idea on how to diagnose the no power problem but i do appreciate if someone can provide the instruction and help where needed.
Hope that this laptop can be revived instead of being added to the landfill. Thank you in advance.

[mcplslg123]

Re: Dell laptop model PP24L won't start from ac adapter

We can assist you but its not an easy job.You need good understanding of schematic,lese you wont be able to grasp what we suggest. Next will be measuring on pins of small IC's. You need needle like probes to do that. Are you ready to handle all this? I'll suggest to seek a professional techie's help offline. Every problem cant be solved online specially if people on both sides are not well versed with nuiances.

Still, if you want to continue,let's know.

[mikey5791]

Re: Dell laptop model PP24L won't start from ac adapter

Hi mcplslg123,

Yes, i am willing to take the challenge and
wish to continue to diagnose the no power problem although i knew it is not an easy job.
Hope that you have the patience and clear instruction for me to follow. Thank you.

[mcplslg123]

Re: Dell laptop model PP24L won't start from ac adapter

What is the resistance to GND on PL5900/PL5901? Resistance to GND on pin19/21 of PU5900? Measure voltage also on these pins and coils. Resistance should be measured without any power source connected.

[mikey5791]

Re: Dell laptop model PP24L won't start from ac adapter

What is the resistance to GND on PL5900/PL5901? Resistance to GND on pin19/21 of PU5900? Measure voltage also on these pins and coils. Resistance should be measured without any power source connected.

The resistance to GND on PL5900 (3.3UH Coil-marked as G3R3 on reverse side of board) is 89 ohm on the 200 ohm scale.

While the resistance to GND on pin 19 of PU5900 (marked as TPS 51120 TI RBJ on my board) is 980k on the 2M scale; and on pin 21 the resistance is 398k on the 2M scale.
Resistance was measured without any power source connected.

Next test is I switched on power source and got these measurements on pins of PU5900 as below: (while black probe is on the nearest ground screw hole)

pin 1 to Pin 8=0 vdc
pin 9=0.17 vdc
pin 10=0.17 vdc
pin 11=0 vdc
pin 12=3.5 vdc
pin 13= 3.5 vdc
pin 14= 3.5 vdc
pin 15=3.5 vdc
pin 16=0.09 vdc
pin 17 & 18= 0 vdc
pin 19=3.5 vdc
pin 20 to pin 27= 0 vdc
pin 28=3.5 vdc
pin 29 to pin 31= 0 vdc
pin 32= 2 vdc
pin 33=0 vdc

Either end of the coil (PL5900) measured 3.5 vdc while power is switched on.

[mcplslg123]

Re: Dell laptop model PP24L won't start from ac adapter

Pin22 is VIN.Are you sure about your measurements? Is there 3V available on PL5900 and 5V on PL5901?

[mikey5791]

Re: Dell laptop model PP24L won't start from ac adapter

Pin22 is VIN.Are you sure about your measurements? Is there 3V available on PL5900 and 5V on PL5901?

Remeasured while power is switched on, from pin 22 i got 30.1vdc
Sorry is my bad. The pins on pu5900 are extremely tiny and so close to each other.
On PL5900 (3.3 uh coil) i got 3.48vdc
On PL5901( the other 3.3uh coil) i got 5.25vdc

[mcplslg123]

Re: Dell laptop model PP24L won't start from ac adapter

Your measurement at pin22 is still wrong,should be 19V. Since you are getting correct voltage at PL5900/5901, lets move on.

Check LIDSW# and on page52,check RUN_on/RUN_ENABLE/+5V RUN/+15VALW. Same for 3.3VRUN/1.8V RUN.

[mikey5791]

Re: Dell laptop model PP24L won't start from ac adapter

Your measurement at pin22 is still wrong,should be 19V. Since you are getting correct voltage at PL5900/5901, lets move on.

Check LIDSW# and on page52,check RUN_on/RUN_ENABLE/+5V RUN/+15VALW. Same for 3.3VRUN/1.8V RUN.

Sorry, i can't locate where is this LIDSW# on my board. Kindly point out the location.
On page 52 of schematic, RUN_ENABLE seems connected to pin 4 of PQ43. While power on, pin 4 of PQ43 has zero voltage.
RUN_ON is connected to pin 1 gate of PQ50(3 pin 2N7002) but i can't locate PQ50.
+5VRUN is connected to PC180(10uf/16v cap) but i can't locate PC180.
+15VALW is connected to PR180(100k ohm resistor marked 104) but i can't locate PR180.
3.3VRUN is connected to PC187(10yf/10v cap) but i can't locate PC187.
1.8VRUN is connected to R88(1k ohm) but i can't locate it.
Btw, are you requesting me to check the voltage while powering on? I am attaching 2 images of the board near PQ43 for reference.

[mcplslg123]

Re: Dell laptop model PP24L won't start from ac adapter

Since you cant locate the components, measure these pins on U15(SIO)

26/127/3/11/74/120/124/16/48/95/67/72/76/78/90/14

[mikey5791]

Re: Dell laptop model PP24L won't start from ac adapter

Since you cant locate the components, measure these pins on U15(SIO)

26/127/3/11/74/120/124/16/48/95/67/72/76/78/90/14

On my board U15 is ITE8512E, my dc voltage on the pins below are as follows:
Pin 26=3.48
Pin 127=3.48
Pin3=3.36
Pin11=0
Pin 74=3.48
Pin 120=3.43
Pin 124=0
Pin 16=3.48
Pin 48=3.48
Pin 95=0
Pin 67=3.18
Pin 72=0
Pin 76=0
Pin 78=0
Pin 90=3.42
Pin 14=2.35

[mcplslg123]

Re: Dell laptop model PP24L won't start from ac adapter

Pin14 should be 3.3V. Another problem is pin95(RSMRST)-this too should be 3.3V. However, when pin14 is pulled low, pin95 cant have any voltage. So the main problem is pin14(WRST#) at 2.35V.

[mikey5791]

Re: Dell laptop model PP24L won't start from ac adapter

Pin14 should be 3.3V. Another problem is pin95(RSMRST)-this too should be 3.3V. However, when pin14 is pulled low, pin95 cant have any voltage. So the main problem is pin14(WRST#) at 2.35V.

What can be the reason pin 14 is pulled low at 2.35v? I tried traced pin 14 to the nearby component for continuity since there is no component marking. As per schematic I traced back the WRST is connected to R6966(470k ohm resistor), D4621, and C7123 (2.2uf 6.3v cap). On my dmm, R6966 measured 448k ohm at 2M ohm scale, D4621 is not open, C7123 measured 2uf on capacitor meter.

[mon2]

Re: Dell laptop model PP24L won't start from ac adapter

EC_RST# voltage is dependent on the pull up voltage of the same cluster of parts you just reviewed.

What is the voltage to ground of +3.3V_RTC_LDO?

Review U12 for the same reason which creates +3.3V_RTC_LDO.

Remove all power and check the resistance to ground of c639.

Flux and remove D10 and confirm that this LDO regulator is able to provide a stable 3v3 without D10.

[mcplslg123]

Re: Dell laptop model PP24L won't start from ac adapter

@mon2 has already suggested. EC_RST@ is pulled up from 3.3V_RTC_LDO-so check as per his suggestions besides checking Q122/Q121

[mikey5791]

Re: Dell laptop model PP24L won't start from ac adapter

@mon2 has already suggested. EC_RST@ is pulled up from 3.3V_RTC_LDO-so check as per his suggestions besides checking Q122/Q121

Voltage to ground of +3.3v_rtc_ldo is still zero.
As per U12(schematic page 41) it is a 5 pin Max1615 regulator, whereby pin 3 is connected to D10. D10 is not open or shorted.

When power is removed, the resistance to ground of c369( your typo c639) is 9k on 200k ohm scale.
Fyi, i had not removed D10 yet since it is not open or shorted. But i found one diode to the left side of the 5 pin regulator is shorted as my dmm measured full continuity on both side. So i solder and lifted one leg of the diode.(refer image)
After power on, i got 3.48vdc on one diode nearest to the screw hole on top. But there is still no voltage on D10( diode on right side of the 5 pin regulator).
I am attaching image of area around the 5 pin regulator before the diode was lifted one leg and next image is after one leg lifted.

[mcplslg123]

Re: Dell laptop model PP24L won't start from ac adapter

First, lets findout which one is D9 and which one is D10. Try continuity test between C369,pin1 to both diode pins-The one which buzzes is D10. Confirm whether D9 or D10 is shorted.Then remove the shorted diode and measure it outside the circuit-does it buzzes or its the pads on pcb which are shorted?

[mcplslg123]

Re: Dell laptop model PP24L won't start from ac adapter

Just on the side of 24 Mhz crystal, some component seems missing. Double check it.