I got a problem with my Dell Presicion 7710

[moxm98]

Hello, I would be happy if someone could help me! To me first: Im from Germany and my English is therefore not perfect! nvm..

I got a problem with my Dell Presicion 7710 with Motherboard No. LA-C551P REV2.0.

NO POWER!

I have done every ordinary thing, such as resetting CMOS and leaving the RTC battery out for a while. It is completely dead, no light, nothing. The powersupply outputs 19.5V and the DC plug measures fine. I have inspected the board, and nothing seems to be obviously damaged, no burn marks, and no apparent water damage. The next step is to check for shorts, however, how would I go about doing that? I don't have a bench powersupply, so it is difficult for me to inject voltage and check with alcohol evaporation etc. I measured the voltage on the JPB1 (ON/OFF-button) and on Pin1 i got 3V. On pin 2 i should get 5V, but theres missing -> 0V. So i looked up in schematics and followed the track to 5VALWP. And the 5VALWP comes from the PU101 with is the powercontroller maybe? So measured the voltages on the PU101 pins and realized that the 5V were missing. The 3V were there, but no 5V.

Here are my measurments on PU101:

Pin 1 = 1.12V
Pin 2 = 0V
Pin 3 = 3.13V
Pin 4 = 0V
Pin 5 = 0V
Pin 6 = 3.13V
Pin 7 = 0V
Pin 8 = 0V
Pin 9 = 4.6V
Pin 10 = 0V
Pin 11 = 0V
Pin 12 = 19.35V
Pin 13 = 5V
Pin 14 = 0V
Pin 15 = 0V
Pin 16 = 0V
Pin 17 = 4.6V
Pin 18 = 0V
Pin 19 = 0V
Pin 20 = 3.13V

Anyone willing to give a bit of guidance?


Schematics and boardview: https://www.badcaps.net/forum/showthread.php?t=115320

[Sephir0th]

Re: I got a problem with my Dell Presicion 7710

You have likely a short to GND at one of the ALW rails. Remove power, meter in resistance to mode. Resistance to GND of PU101 Pin8 and Pin 18?

[moxm98]

Re: I got a problem with my Dell Presicion 7710

On Pin 8 the resistance floats between 4k-8k ohms and on Pin 18 floats between 20k -21k ohms.

[Sephir0th]

Re: I got a problem with my Dell Presicion 7710

Interesting. Identify PL101 and PL102. Meter in voltage mode. Red probe already the coil, and black probe already to GND before pressing the power button. Any spike to catch? Do this with both coils.

Another question would be whether the charger is known good and of correct wattage. Can you clarify?

[moxm98]

Re: I got a problem with my Dell Presicion 7710

On PL101 we got 4V and no difference with pressing power button. On PL102 nearly 0V. When i plug the charger in, PL102 goes from 0V to 14,5mV.

Its the original charger from Dell with 240W 19,5V -> 12,3A.

Btw: thanks for your help!

[Sephir0th]

Re: I got a problem with my Dell Presicion 7710

Unfortunately we have a Problem now. At least one of your measurements is confirmed wrong, since PL101 and PU101 Pin 8 have continuity.

You have to sort that out first before we can continue. And this applies to any measurement you have done so far. Otherwise the assistance here would misleaded and the case probably end in being a no-fix

[moxm98]

Re: I got a problem with my Dell Presicion 7710

Yep.. measured again and now we got both nearly 0V. PL101 ist fix at 0V. PL102 stays stabile at 3mV.

could that fit?

[mcplslg123]

Re: I got a problem with my Dell Presicion 7710

Resistance on pin8/18 is healthy. You have both 3/5V LDO as well both the enable's are present on pin6/20. So replace PU101.

[Sephir0th]

Re: I got a problem with my Dell Presicion 7710

Agree. I'd suggest tonreplace all 4 related mosfets too. If nothing helps, deep troubleshooting of this circuit is necessary. Also check whether the controller is getting hot by any chance.

[rediii]

Re: I got a problem with my Dell Presicion 7710

i have had a similar problem with a toshiba protege with a mec ec. in my case the measurements were identical. i had to reball the mec ic and the machine worked fine again. replace 3 V/5V ic and mosfets first, like the others suggested. maybe it helps. good luck!

[moxm98]

Re: I got a problem with my Dell Presicion 7710

okey, i´ll order some of these ic´s. I have one notebook (MB No.: X756UXM) as replacement for some components and I found a ic chip similar to the UP101 (marking says: uP9003Q). Can i use it?

[rediii]

Re: I got a problem with my Dell Presicion 7710

okey, i´ll order some of these ic´s. I have one notebook (MB No.: X756UXM) as replacement for some components and I found a ic chip similar to the UP101 (marking says: uP9003Q). Can i use it?

no, you should replace the chip with TPS51285B