Repairing motherboard audio

[stealthjoe]

Hello,

I have a motherboard M6VLR rev 3.0. It has an onboard audio with the audio codec ic VIA VT1612A. The problem is that there is no audio output despite installing all the required drivers (for win 98 / XP). The sound icon is indeed showing up, but there is no audio output through the speakers. Initially I was suspecting a failed audio codec. So I had ordered 2 of this ic. However before getting into replacing that wanted to first test the capacitors in the audio circuit. Here 2 capacitors (22uF) measured only around 4uF. One more 22uF capacitor measured around 40uF. Finally another 100uF capacitor measured only 4uF. However, none of the capacitors had any visible damage/signs of failure as given in the attached image. The 2nd image having the caps with green markings are the problematic ones.

Was curious to understand if such very low capacitances in the audio circuit could cause no audio output? Please let me know your thoughts. Thanks!

 

[Diver300]

Yes, low capacitance (and high ESR) can happen with no visible signs of damage. In fact that is the normal failure mode.

It is rare that there is no audio output, it is often really, really quiet.

It can be difficult to measure capacitance with the capacitors still in the circuit board.

If I have understood correctly what is going on, that is a 20+ year old PC. My suggestion would be to change all the electrolytic capacitors. The cost of the capacitors is so small that it does not seem worth trying to remove them to measure them. You may find it safer for the motherboard to cut the capacitors so that the legs are separate and you can then unsolder the legs one at a time. All new capacitors must be the right way round, and should be the same capacitance (although larger would most likely be fine). The voltage rating must be at least as big as the originals, but you can go for larger voltages if you want. The temperature rating should be as high as you can find, preferably higher than the original ones, as the higher temperature ones will last longer.

 

[stealthjoe]

Thanks for your reply. I got this board around 3 years back and the onboard audio wasn't working ever since. I did try testing the continuity between the line out pins and the line out socket, but was getting the beeps only with the ground pins on the IC. I am confused if it could mean a defective one. Any other possibility to check the cause? Attached is the datasheet.