TS9 Bypass Issue?

[dumbmonkey]

Hi everyone,
I have a TS9 that a friend gave me to "take a look at".  At first it seems that the effect on mode is considerably quieter than it should be, but after trying the guitar with and without the effect, it's actually the bypass mode is way louder than it should be.  In other words guitar into amp without pedal is at one volume, guitar into amp with pedal bypassed is louder, guitar into amp with effect on is back to the original volume level. 
Has anyone ever experienced this issue, and have any insight?
Thanks in advance!
Chris