Possible solutions for burnt-out circuitry on Dell Latitude D505 mobo?

[jvadillo]

Hello,

I've read arrived at this post as I have the same problem with a Dell inspiron 1520, when I connect the power adapter to the wall plug the green led lights on, but as soon as I connect it to the laptop the light turns off.

I have ruled out the adapter being a problem as I tested it on another inspiron 1520 and it works fine, while another adapter does the same on the "bad" inspiron 1520.

I opened and removed the motherboard, it has 5 capacitors PC1 to PC5 close to the plug for the power adapter and they all seem fine with resistance of 0.5kohms to 250kohms. I then checked the PC capacitors close the the connector for the battery (it has like 20 with the "PC" mark) and at least half of them show a resistance of 1.3Ohms.

Is that normal or with such low resistance I can consider them as being in short circuit?

Any ideas on what else to look at? Or maybe the mother board is beyond repair?

Thanks in advance

[kennedytham]

brimar,

I also have the same issue - my D505 works off battery but battery won't charge, and if you plug in the PS the light on the brick goes out. I have my mobo in front of me and see the mosfet you're talking about (PQ12 is silkscreened next to it).

Not sure where the ceramic cap might be on the underside. You mention CP13, but all the power-related components on my mobo appear to have a P before the component type (PC, PQ, PR, PD, etc.) I found a PC13 in line with the PV3 flexible contact on the underside next to where the power connector is mounted. Hard to tell from visual inspection if it's bad.

I suppose it could be any of the caps in the power circuit, though...

How did you connect your low-output PS at your test-bench, and could the resistance test setting of a multitester work as a low-output PS for the purpose of heating up the defective cap?

(edit) Never mind - I found that cap has a dead short across it using my multimeter's continuity test. Replaced it with one the exact size & shape I snagged from a bad Inspiron 5100 mobo... I'll post back with the results.

(edit) That did the trick! You're a genius! This little "secret" has GOT to be shouted from the rooftops.

That just goes to show you that a dead component doesn't have to have any visible signs of damage.

Thanks for the your info..now I success fix my XPS1210 by removing CAP PC07.
Thank you very much..

[compay]

Just repaired a laptop with the same symptoms:
Won't charge the battery, won't power from AC.
Also if you power the AC adapter when not connected to laptop you get green power LED on the adapter. When you plug it in the laptop the green power LED immediately goes out.

Opened it up and found SO-8 P-ch mosfet by the DC input socket. Source (pins1,2,3) is connected to the inner barrel (+19.5V), Gate 4 gets driven low, applying the input to the Drain. (pins 5,6,7,8) On my board the drain was short to GND. Applying power directly to the Drain via a current limited bench PSU (set 1A limit) showed a couple of volts.

Placing a finger on the opposite side of the board revealed a SMT ceramic cap getting hot.
CP13 I think. Opposite side to the power connector, almost under it. I would guess at 1206 or slightly larger and there is an 0402 cap just next to its bottom pad at 90 degrees to it. Cap was glued before soldering so had to flow both sides at the same time with a soldering iron and force off. Would likely have been 1uF or bigger 25V. Removal restored operation. Runs OK without but would suggest putting something in there 0.1uF 1206 50V, perhaps a couple stacked ?

BTW you have to strip down everything and remove the main board to get to the cap :-(

Hope this info is of use to someone....

(EDIT) correction: cap is PC13. Pic showing location of failed cap - D505fix

Robin
die4laser.com

Just fixed mine using your info.
THANKS A BUNCH

[nitram987]

Yep. Same thing. My shorted cap was PC39 (it was a 10uF, 25V capacitor, as verified on the schematics for that board). It looks like mobo manufacturer Quanta (that made the Dell Inspiron 1520 motherboards at that time) had some long-term capacitor reliability issues.

[Chuckiechan]

Welcome to Techimo!

Be sure to check the date of the original post...

Happens to everyone...