TC Electronic Sustain+ Parametric equalizer issues

[zintolo]

Hi,

I've bought this 80's stompbox (schematic in attachment) and it has some issues:

• when bypassed the led goes off 1 second, then comes back to medium brightness;
• when unbypassed (second press of the bypass switch) the led goes full brightness;
• the sustain effect is like always present (even when bypassed) but subtle;
• the parametric eq is never present.

First two makes me think that IC3 (LM339) has some issues and it is not driving IC4 properly.
What do you suggest me to try?

Thank you all in advance,
Roberto