I haven't seen your soundchip, but on most of the ones I've dealt with there are a number of mic settings under alsamixer. Here's a script I use to initialize my mixer. Your "numid's" will probably be different,but it will give you an idea what to look for.
You can get a list of what you have and how they are set with this command. Redirect it to a file as it will be long:
amixer contents
Pay particular attention to "Mic Select." Most on-board sound chips have a lot of features that aren't implemented on the motherboard. Multiple mic's are one, and the wrong one may be selected. Also check "Capture Source" if you're trying to record from the mic.
My script:
#############################################
# Mic Boost (+20dB)--numid=15--type=BOOLEAN #
#############################################
A="amixer cset numid=15 1" ; $A > /dev/null
if [ $? != 0 ] ; then echo $A ; fi
# : values=off
#########################################
# Mic Select--numid=32--type=ENUMERATED #
#########################################
A="amixer cset numid=32 1" ; $A > /dev/null
if [ $? != 0 ] ; then echo $A ; fi
# ; Item #0 'Mic1'
# ; Item #1 'Mic2'
# : values=1
###############################################
# Mic Playback Switch--numid=13--type=BOOLEAN #
###############################################
A="amixer cset numid=13 0" ; $A > /dev/null
if [ $? != 0 ] ; then echo $A ; fi
# : values=off
#######################################################
# Mic Playback Volume--numid=14--type=INTEGER--max=31 #
#######################################################
A="amixer cset numid=14 31" ; $A > /dev/null
if [ $? != 0 ] ; then echo $A ; fi
# : values=31
#############################################
# Capture Source--numid=26--type=ENUMERATED #
#############################################
A="amixer cset numid=26 5" ; $A > /dev/null
if [ $? != 0 ] ; then echo $A ; fi
# ; Item #0 'Mic'
# ; Item #1 'CD'
# ; Item #2 'Video'
# ; Item #3 'Aux'
# ; Item #4 'Line'
# ; Item #5 'Mix'
# ; Item #6 'Mix Mono'
# ; Item #7 'Phone'
# : values=5,5
#@%!! Windows!
