Vostro 3560 (LA-8241P) dead short to ground

[spleenharvester]

Re: Vostro 3560 (LA-8241P) dead short to ground

Actually would this be an OK choice for a soldering station, if I needed to replace a small ceramic cap for example? https://www.amazon.co.uk/Tuloka-Elec...ct_top?ie=UTF8

[spleenharvester]

Re: Vostro 3560 (LA-8241P) dead short to ground

Found our culprit (or one of them at least!)

I noticed a small 'nick' in one of the ceramic caps connected to PL101, see pic (it was less obvious without the flash... I swear!), with a bit of debris stuck to the side of it... I thought maybe it was accidental damage from constant testing of the board, so I tried the 9V battery across B+ a final time and touched it... lovely capacitor mark burned into my finger

I believe it is either PC103 or PC104 shorted as they are the two capacitors in that particular group with the same size and rating...

1) Should I now acquire a 4.7uF, 25V, 0805 package ceramic cap (have I interpreted that correctly?)

2) Is it safe to apply power with this damaged capacitor removed?

3) The schematic specifies an AO4407AL on PQ100 but it is actually an MDS3504 on this revision of the board... can I replace with AO4407A as that is more easily acquired in my country? (I figure I am likely to need to replace this given these types of shorts seem to kill either high side or low side VIN?)

Many thanks!

EDIT: Oh PS the marks on the charger IC and other caps are just from a sticky plastic insulator that was on there (hence why I didn't look terribly closely at this cap originally).

[spleenharvester]

Re: Vostro 3560 (LA-8241P) dead short to ground

Update - pulled the cap and the short is gone, system powers up, fan spins up and down as if it's about to POST... then I get output to an external monitor, but it is just solid black. PCH slowly starts to get very hot. Is this a dead PCH, or can other things be tried? Is this possibly due to not having replaced the capacitor?

EDIT: I note also that the battery does not charge, although the system appears to fire up fine from both battery and AC.

[ktmmotocross]

Re: Vostro 3560 (LA-8241P) dead short to ground

that capacitor is a part of some capacitors to filtering voltage from step-down mosfets. so just throw to it any capacitor this size and voltage. what is that regulator for? what it feeds?

[spleenharvester]

Re: Vostro 3560 (LA-8241P) dead short to ground

So with the CPU removed, PCH does not heat up - is it possible that the CPU is just dead or would this be expected if the PCH were shorted?

GPU still heats up, but I don't think it heats up by an abnormal amount.

that capacitor is a part of some capacitors to filtering voltage from step-down mosfets. so just throw to it any capacitor this size and voltage. what is that regulator for? what it feeds?

Okay thank you - if I am right in thinking you mean PQ100, it is the first MOSFET that VIN from adapter reaches. It seems to be OK though as the board is firing up.

[spleenharvester]

Re: Vostro 3560 (LA-8241P) dead short to ground

Tried new CPU, exactly the same thing, powers on with a backlight-only black screen on boot, with the PCH gradually getting very hot over about a minute or so. Any ideas, or is this likely to just be a dead PCH (and hence belong in the bin)?

[ktmmotocross]

Re: Vostro 3560 (LA-8241P) dead short to ground

So with the CPU removed, PCH does not heat up - is it possible that the CPU is just dead or would this be expected if the PCH were shorted?

GPU still heats up, but I don't think it heats up by an abnormal amount.



Okay thank you - if I am right in thinking you mean PQ100, it is the first MOSFET that VIN from adapter reaches. It seems to be OK though as the board is firing up.

no, i mean circuit with that bad capacitor

[spleenharvester]

Re: Vostro 3560 (LA-8241P) dead short to ground

I think I'm going to have to give up on this board as I cannot for the life of me figure out why it will not POST - I am fairly sure I have measured every rail as voltage being OK.

no, i mean circuit with that bad capacitor

It appears to be something to do with battery charging - connects B+ with CHG_B+ and one of the first BATT+ MOSFETs. Screencap of schematic:

[piernov]

Re: Vostro 3560 (LA-8241P) dead short to ground

Would be better to replace it but this capacitor does not really matter.
About the POST issue, make sure you're using working and compatible CPU, working RAM, working display and display cable. Try a clear CMOS and check the CMOS battery voltage.
Then if you still have no activity (caps lock led not lighting up after pressing caps lock key for example), check the BUF_CPU_RST# signal.

[spleenharvester]

Re: Vostro 3560 (LA-8241P) dead short to ground

Would be better to replace it but this capacitor does not really matter.
About the POST issue, make sure you're using working and compatible CPU, working RAM, working display and display cable. Try a clear CMOS and check the CMOS battery voltage.
Then if you still have no activity (caps lock led not lighting up after pressing caps lock key for example), check the BUF_CPU_RST# signal.

All components are tested working on a different (working) vostro 3560, and CMOS battery = 3V, cleared with no effect. Caps lock lights up and down if pressed under normal conditions, but can confirm that BUFO_CPU_RST# is present @ 1.05V (unable to locate RC34, CC63 and RC33 to test BUF_CPU_RST# directly).

It is worth clarifying that LVDS is not currently in use - all testing is on external monitor, and that the PCH heats up more quickly if an external monitor is plugged in.

[spleenharvester]

Re: Vostro 3560 (LA-8241P) dead short to ground

Worth noting that there is:

a) A ctrl+alt+delete response to reboot the board

b) There is an Fn+F1 (external LCD switch) response (but this usually results in the fan going crazy and the system locking up, as denoted by the lack of a caps lock response only after pressing Fn+F1; PCH also gets very hot during this time)

c) Freeze-spraying the PCH surrounding area of the board causes loss of caps lock response and loss of a number of voltages eg +VCCSA and some 5V rails, which persists until the board warms up again

[dellxps15]

Re: Vostro 3560 (LA-8241P) dead short to ground

i would replace the pch.

[spleenharvester]

Re: Vostro 3560 (LA-8241P) dead short to ground

I feared as much, as I don't have the tools to do that here. I may have to move this board to trash now sadly!

[spleenharvester]

Re: Vostro 3560 (LA-8241P) dead short to ground

So I couldn't resist having a bit more of a play around with this board I found that 3V is present across the one capacitor mounted on top of the PCH next to the core, and when I inject 3V across this cap with the board powered down it replicates the PCH heating up (pulls approximately 0.6 amps). Is this conclusive evidence that the PCH is dead, or can other things cause this behaviour? Does the 3V on that cap correspond to a 3V rail on the board?

Also I checked a number of signals connected to UC1 eg PCH_PWROK and all of these seem fine

EDIT: Injecting 3.3V at JP8 (either 3VS or 3VGS) also causes the PCH to heat up. 3VS reads about 350~ ohms to ground

[spleenharvester]

Re: Vostro 3560 (LA-8241P) dead short to ground

Focused my efforts on the backlight circuit, and I believe QV3 is shorted. At QV3, there is 5V on one leg (I believe this is D as it measures 100ohms to QV4, but not 100% sure), ground measures... to ground, but G measures at 4.4ohms to ground unexpectedly and 0V. Injecting 3.3V voltage at QV3 leg G causes QV3 to get scorching hot.

However, QV3 does not seem to be heating up particularly when the system is powered on. Is it possible that it is causing the PCH to appear as shorted?

Also all legs of DV7 read 0V and <100ohm resistance

[piernov]

Re: Vostro 3560 (LA-8241P) dead short to ground

What about QV5? Since it seats inbetween QV3 and DV7, if it's OK then QV3 would not have any effect on the PCH. If it's bad then it may explain some things.
Also with the information on this part of the schematics, I understand that LCDVDD should be 3.3V (which sounds reasonable) whereas you're saying that you get 5V there. Am I missing something?

[spleenharvester]

Re: Vostro 3560 (LA-8241P) dead short to ground

What about QV5? Since it seats inbetween QV3 and DV7, if it's OK then QV3 would not have any effect on the PCH. If it's bad then it may explain some things.
Also with the information on this part of the schematics, I understand that LCDVDD should be 3.3V (which sounds reasonable) whereas you're saying that you get 5V there. Am I missing something?

QV5 reads as 5V on one leg, 0 on the others, I will have to wait for my new multimeter probes to get here before I can test further. Injecting voltage into either leg doesn't cause it or the PCH to heat up.

I have a feeling that I have misunderstood the schematic somehow as I think the 5V I am reading on QV3/QV5 is +5VALW and it is actually injection into the +LCDVDD leg that is shorted. I'll have another look at this when my new probes get here.

EDIT: Removed QV3, no change, PCH still heating up when system is switched on (though oddly doesn't heat up quite so much as before when 3.3V is injected across the PCH cap). PCH still does not heat up without CPU installed

[spleenharvester]

Re: Vostro 3560 (LA-8241P) dead short to ground

Final bump before I (actually ) scrap this board - any ideas other than replacing the PCH?

[spleenharvester]

Re: Vostro 3560 (LA-8241P) dead short to ground

So interesting twist - I have acquired another LA-8241P, this one a non-GPU version (with a damaged keyboard connector). Having tested this one in the same manner, I have found that the PCH also gets really hot on the working board - so seems like this may not be the cause of issues with my non-posting LA-8241P?

What else could it be, I assume either GPU or BIOS?

[caspian]

Re: Vostro 3560 (LA-8241P) dead short to ground

Now you should discover what else gets hot on the board, including CPU, GPU, SIO, and smaller chips.