Continue ahead and go through the fizzler. You end up in a control room. Go through the side door to find a big conveyor belt with dead turrets on it. A computer voice tells you not to talk to turrets on the conveyor belt.
Create a portal on the wall above where the conveyor belt is coming out, and create a portal of the opposite color inside the office. Go through. Go near the end of the conveyor belt and jump onto the platform there. From there, jump onto the vent. Go along it to reach the second conveyor belt. Walk the opposite direction along the conveyor belt. If you see a turret with its laser blinking, pick it up to get an achievement. Keep carrying it to hear it say some rather interesting things.
Near the opening of the conveyor belt (where the belt is coming out from) there are more vents down below. Jump down onto the vent there. Go forward a little and then look down to the side. There is a walkway down there. Drop down to it. Continue along the walkway until you reach a fizzler. Go through.
To the left you see a turret testing line. There is a white ceiling above the human dummy. Make a portal on that ceiling such that you'll drop behind the wall with the dummy. Then make a portal on the wall behind you and go through.
Look at the wall behind the turrets and make a portal there when you can safely do so. Now you need to make a portal on the wall behind the dummy. Carefully do so when one of the malfunctioning turrets is there (so you won't get shot) and go through.
Continue along the path to reach another turret testing area. The defective ones are thrown into a chute. Catch one of the defective ones, then continue along. You'll run into Wheatley again. Up ahead you'll reach the room with the master template turret. Wheatley will want to hack the door so you can remove the template. He'll ask you to turn around while he does it. Afterward, you'll see that the glass in the window was broken.
Put down the defective turret, then create a portal in the master turret room, and a portal of the other color that you can reach. Take the defective turret through. Remove the master turret, and if you want to unlock an achievement, stand in the scanner. Then replace the master turret with the defective one.
Now exit the master turret room and go toward Wheatley. He'll go over to hack the exit door and tell you to watch the turret line. Check on the door and it eventually will be open. Go through. Wheatley will be surprised that the door was already open in spite of his continued "hacking" attempts.
Follow Wheatley and you'll reach a sign that says Neurotoxin Production to the right, employee day care to the left. You have to go through the employee day care, so do that. Wheatley will walk you through the potato battery science exhibits from Bring Your Daughter to Work day.
Continue along the path until you reach a couple of automatic doors. Go toward the second one to trigger the loading screen.