Boss TU-2 issues

[dumbmonkey]

I was wondering if anyone could help shed some light on this.  I recently was given a non working Boss TU-2 by a friend.  It had taken a number of beer baths and was a disaster to look at, in addition to having a gummed up switch.  I replaced the switch and cleaned the unit and it seems to work fine except that now the check indicator is on even when the pedal is bypassed and I'm getting some crackling noise through the pedal. The tuning works just fine, it just seem to make noise.  Anyone have any thoughts on this?

[dumbmonkey]

Update for those of you keeping score at home.  There wasn't any crackling, it seems it was just me being stupid with cables.  The tuner works fine, in bypass and tuning mode.  The check indicator is still on but goes off periodically.  I'm assuming it has something to do with the switching circuit, but as it's not causing any issues, I really don't care. C'mon, free tuner? What's not to like...