Boss OC3 help - low signal volume after true bypass

[FausterCraster]

Hi, in trying to put a true-bypass system in a OC3 I just connected the jacks and the FX input/output wires to a 3PDT.

This pedal has a knob selector for Drive/Oct2/Poly
when it is on Oct2/Poly position, sound is very low; I can hear the octave but signal but is vary low. When it is on Drive signal volume is 1:1 with dry one (so drive position is ok...)

I can't find any schematic on web for checking.
Anyone has the circuit diagram/schematic ?

Any suggestion ?
I can post some picture; just let me know.

Thanks

[FausterCraster]

I reopen the pedal to take out the 3PDT and to take some photos.

Even in bypass mode (buffer only) the signal is really low.
....am I losing some ground ?

TX

[apollomusicservice]

#3 BRN wire to Input
#4 YEL wire to #2 for Bass or open for guitar
#2 BLK wire to Ground
#14 WHT to Out
if you use battery than Battery BLK/BLu to "ring" of input jack