Hi mura,
Check the solder joints around where you were working. You either have a solder bridge, or short, or you have desoldered a component. Also give the unit a shake in case you have some stray solder bits.
Hi mura,
I am not familiar with this unit. Does it have tone controls? Possibly a broken tone control pot? Normally you would have to replace a capacitor with the wrong value.
Can you have another tech look at it? Another set of eyes can fix any things.
-Chris