Thinkpad T420, speakers don't work

Hi,

Not all the liquid would have drained out as evidenced by the residue shown in your picture.

Is there audio available at the headphones socket?

If there is audio at the headphones socket I suggest that you try and gently clean all of the residue off using Isopropyl Alcohol 99%+ and a Q-Tip, especially where it covers the circuit board as shown in the picture.

As always when working on electronics (except when testing) disconnect the power from the systemboard to prevent any possible problems from occurring due to “accidents”. The Power button is not a power isolating button and power is still available at various points on the systemboard. Also be careful not to damage the board or any components or tracks covered by the residue

It may be that the residue is conductive and is the cause of the problem.

Normally what happens is that when headphones are plugged in, an internal contact in the socket is operated and depending on the type of socket, it either breaks the audio connection to the internal speakers and switches the audio to the headphones or it sends a signal to the BIOS/OS which software switches the audio away from the internal speakers onto the headphones. So given that there is an indication that there are headphones plugged in you are probably right in suspecting that the BIOS "thinks" that there is something plugged into the headphones, when nothing actually is.

If there is no audio available at the headphones socket perhaps the socket (audio board?) is faulty and your cleaning attempt didn’t resolve the problem.

On p.140 of the service manual it shows that there is a audio sub board (part #9 shown on p.134). When searching online using the part number only (04W1623) the part is available. (It seems to be very expensive for just an audio card)