HP 840 G5 Shorted Audio IC

[chbalnuweit]

Hi all,

so I made a stupid mistake and dropped a screw onto the motherboard while assembling it.
The screw fell right onto the battery connector area and unforunately managed to short one of the supply voltage lines of the Audio IC (Conexanct CX 7750) without me noticing at first.

After the assembly and booting Windows I noticed that there was no sound and no Audio IC detected in device manager...

I got the motherboard out again and found the Audio IC with a crater in it...
Luckily I got a donor board with the same model motherboard.

I desoldered the old IC and soldered the new one in place.
Unfortunately the Audio IC is still not detected by Windows or Linux, even tho I hear the Bios beep when booting.

I measured all the supply voltages around the chip and they all seem ok. I used a schematic of CX7750, since thats all I could find. (see attachement)

3V at pin 3 and 9
3V at pin 4 and 5
1.8V at pin 46 and 20
5V at pin 15, 18 and 34

I tested every pin in diode mode and could not find any shorts.

From what I understand, the PC_BEEP signal from Bios is analog and would work even without the Audio IC being detected "digitally"
Is it possible, that the data lines to the PCH are burnt? Or that the PCH itself got damaged? Everything else seems to work fine tho...

Any idea on how to diagnose this further?

Thank you in advance!

Christian

[Sephir0th]

Re: HP 840 G5 Shorted Audio IC

Clear pictures of your Job please, to start with.

[chbalnuweit]

Re: HP 840 G5 Shorted Audio IC

Sure, here are a few phone camera photos and a screenshot of my (rather shitty) USB microscope.

Note:

Pin 4/5 are together so the bridge shouldnt matter. I couldnt get them to seperate...

[loopster]

Re: HP 840 G5 Shorted Audio IC

Excuse my weak eyesight, but are you sure about these two?
They look bridged,too.

[chbalnuweit]

Re: HP 840 G5 Shorted Audio IC

Hi, thank you for looking into it :-)

I saw these two pins as well but according to the schematic Pin 26 is HP_OUT_R_R and Pin 27 is PORTM_MONO and not connected to anything.
I tried to remove the bridge with my soldering iron after soldering the chip using my hot air station, but it was not fine enough to get rid of the bridge...

My next investments will definitely be a better soldering iron and microscope.. these chips are getting tinier and tinier ;-)

edit: I tried again and used my iron, solder wick and a lot of flux and dragged it along the side of the chip and was finally able to get rid of the short between pin 26/27 .. unfortunately the chip is still not showing in Windows or Linux.