Attempting to fix a mixer VU meter

[little dude]

I have a Samick 16 channel mixer where the left channel VU bar graph stays full on. Ive searched for a schematic with no luck and have checked most of the componants on the left channel PC to find nothing out of whack.

If anyone has a schematic or could point me to one would be very appreciated.

[jrfrond]

In general, the reasons for this could be:

1- Open ground in meter circuit

2- Audio oscillation

3- Bad display drive IC (very often either LM3914 or LM3915)

I do NOT have a schematic, but as an experienced tech, these are three possibilities.

[little dude]

It uses a Sharp brand 22 pin IC for the display, I dont have the number handy.

This meter can view the left channel output along with the sum level via a pushbutton. When the button is enabling the sum view it causes an increase in the left channel output level.

It uses a 20k trim pot bridging the Vmin and Vmax together. I checked it and it seemed open. I remove it and check it and it would show no value on a meter. I check it again later and its showing proper value.

During various checks I found if you run a source through a channel and the left fader with both in the full fader the display will operate backwards meaning as a sound level peaks the meter will drop out LED's from top to bottom.

[little dude]

IR2406G is the Sharp chip. It has three OP amps in use, two 1022B and one 1007B.