Dell laptop model PP24L won't start from ac adapter

[mikey5791]

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?

By continuity test, found the diode next to 5 pin regulator buzzes which is D10. The diode on top D10 should be D9, but it measured 63 on both side during diode test. So is D9 is open. Should i remove its one leg for further testing?

Also, i am not too sure on checking for any missing component around the 24Mhz crystal since i could not locate it on the schematic.

[mon2]

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

Yes, lift one leg and then check the diode in diode mode again to see if the diode is defective.

[mikey5791]

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

Yes, lift one leg and then check the diode in diode mode again to see if the diode is defective.

Yes, that D9 diode was lifted one leg and measured 63 (both side measured 63 after swap dmm probes) on diode mode. Confirmed this diode is defective. What spec of this diode and is it necessary to get a replacement or substitute?

I tried power on and measured voltage on reverse side of board on pin 14 of U15. No power at all.

[mcplslg123]

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

Better completely remove the diode and check it outside circuit. repeat the diode mode test on both pads of diode D9 on PCB. The diode may be defective but the reading can be from PCB pads-so lets make it sure.

[mikey5791]

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

Better completely remove the diode and check it outside circuit. repeat the diode mode test on both pads of diode D9 on PCB. The diode may be defective but the reading can be from PCB pads-so lets make it sure.

Done completely removed the diode D9 and did a diode test outside circuit. It reads 63 on both side and it is a shorted diode. When i performed diode mode test on both pads of diode D9 on pcb, i got reading of "1" on one side and about 836 on other side. I also did resistance to ground test. While black dmm probe on screw ground, red probe on diode D9 lower pad, the resistance is 154.4k on 200k ohm scale. If the red probe is put on diode D9 upper pad, the resistance is 1.01M on 2M ohm scale.

Fyi, i also did diode test on diode removed from left side of 5 pin regulator. It beeps on both side of diode test. (Reads zero)This diode is shorted.
But diode test on the pads does not read shorted since one side is "1" and other side is about 800.
While on resistance to ground, the upper pad reads "1" on 2M ohm scale and lower pad reads 1k on 20k ohm scale.

[mcplslg123]

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

Replace D9

https://www.nexperia.com/products/di.../RB751V40.html

[mikey5791]

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

Replace D9

https://www.nexperia.com/products/di.../RB751V40.html

Is there any equivalent schottky diode i can use( e.g. SS14 1N5819 1A 40v type are more easily available in our area). Seems like RB751v40 is not that easy to source.
Also another question, how do i identify which pad on pcb is for cathode side of diode? Is that the upper pad with higher resistance is for cathode side? Or the lower pad?

[mon2]

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

While the properties of the diode are not super critical to be matched, they must still be reviewed.

You must, however, 100% match the body size which is a SOD323 (SC-76) Surface-Mounted Device (SMD) plastic package.

https://my.mouser.com/ProductDetail/...9JYjO8ug%3D%3D

https://my.element14.com/search?st=R...468b3fd077744c

So Mouser (Malaysia) is one option but you can check your local stores. Other options are Digikey (Asia) / Arrow (Asia).

[mikey5791]

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

Replace D9

https://www.nexperia.com/products/di.../RB751V40.html

May i know how do i place the new diode on the pads of D9, as in which pad to place cathode side? I tried continuity test on the pad to screw ground but there is no buzzes.
Kindly advice. Thank you.

[mon2]

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

Meter in lowest resistance scale.

Remove all power.

Short your meter probes. This is what you are hunting for between R204, pin #2 and the diode pad for D9.

Once you have located the pad, the resistance should be ~0 ohms. This is the backside of anode of the diode.

The diode package will have a bar on its markings to denote the cathode side. So the bar is not the side of the diode to mate with R204.

If the diode is without a bar, configure the meter into diode mode. Red meter probe to the diode on your table. Black probe on the other side. If the meter conducts, then the red meter probe side is the anode.

Hope this makes it clear.

[mikey5791]

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

Meter in lowest resistance scale.

Remove all power.

Short your meter probes. This is what you are hunting for between R204, pin #2 and the diode pad for D9.

Once you have located the pad, the resistance should be ~0 ohms. This is the backside of anode of the diode.

The diode package will have a bar on its markings to denote the cathode side. So the bar is not the side of the diode to mate with R204.

If the diode is without a bar, configure the meter into diode mode. Red meter probe to the diode on your table. Black probe on the other side. If the meter conducts, then the red meter probe side is the anode.

Hope this makes it clear.

Yes, your explanation was clear. Through your suggestion, i found D9 at which the anode side is connected to R204 and the resistance is zero ohm. This is the initial pad which had a shorted diode reading of zero on forward and reverse diode test mode.
On another note, there is one pad for unknown diode as per my image on the lower left side of the 5 pin regulator. The upper diode pad in blue linehad continuity to first row of middle pin of that 5 pin pad while lower diode pad in yellow line had continuity to left side of that 5 pin pad and a 114.5 ohm resistor. My question is how to identify what value of this unknown diode?

[mon2]

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

Review carefully the components marked in the posted pic as D9 and D10. These appear to be resistors.

Check if they are by using your meter in resistance mode. Meter probes across the part. Note the reading. Then reverse the probes. Same measurement?

The diodes appear to be the 2 parts south in your pic with the 'T4' markings. Check them in diode mode.

[mikey5791]

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

Review carefully the components marked in the posted pic as D9 and D10. These appear to be resistors.

Check if they are by using your meter in resistance mode. Meter probes across the part. Note the reading. Then reverse the probes. Same measurement?

Measured D10 in 200k ohm resistance and got reading of 124.8k on one side and reading of 147.7k on reverse probes.
The diodes appear to be the 2 parts south in your pic with the 'T4' markings. Check them in diode mode.

Measured D10 in 200k ohm resistance scale and got reading of 133.8k ohm on one side and after reverse probes i got reading of 147.7k ohm.
Both T4 measured "1" on forward bias and "443" on reverse bias diode mode.
So, should i resoldered the original parts(resistor?) back on board?

[mikey5791]

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

Both components which i desoldered off board appears to be resistor.
Off circuit, on resistance 200 ohm scale, the resistor on the left side of that 5 pin regulator measured 0.2 ohm( and on diode continuity test it beeps and likely is shorted). The other resistor on the right side of that 5 pin regulator measured 14.8 ohm. Seems like both these resistors are off the expected rating or could be damage since as per schematic on rtc battery, the resistor rating i noticed is at 1k ohm. Should i try replace both these resistors to 1k ohm type? Kindly advise.

[mon2]

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

Check the resistor values against the schematics. If they are 1k in resistance then configure your meter scale to be higher so the meter can measure the part.

That is, do not use a 200 ohm meter scale to measure a 1k resistor.

If you still read around 0 ohms while the resistor is off board then replace it with a known good part. It is possible that a defective resistor will be lower than expected. Unless stated otherwise in the schematic, the accuracy of the resistor is often not critical.

Power supply feedback circuits will use 1% tolerant resistors to keep the power supply rail stable.

[mikey5791]

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

Had been occupied with other matters until recently i changed both the bad resistors to 1k ohm type. Wow, the laptop is powering up to windows after i installed all the board, cables, connectors, etc.
Thank you to all the forum members whom had contributed their time and effort to help diagnose this dead laptop to working condition.

[mcplslg123]

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

Glad to know you revived it.