Needed tools:
screwdrivers PH No.2 and small slot-type ( 2-3 mm );
inbus (x ", sorry, I don't Know ) for the frontplate/bottomplate connection
or, lacking this, pliers

1. Before opening the unit pull out the wallplug
   
   
2. Remove the bottom plate of the unit
   
   
3. You'll see four trimpots on the board
   
   
4. The pot for adjusting the bias of the unit ( which changes the delay time ) is the one most right, when you look at the board with the frontplate next to you and the jacks away from you. It builds the top of a triangle with the 'feedback' and 'width' pots on the frontplate and is the only trimpot that 'lies down' (the other three 'stand upright')
   
   
5. Before changing anything MARK THE CURRENT POSITION OF THE POT !
   
   
6. Replug the unit to the wall, switch it on and connect input and output to soundsource and amp/mixer o.sth.
   
   
7. Crank the ' delay time ' all up and loop something
   
   
8. Now, carefully turn the trimpot clockwise and the delaytime will increase (pitch of the loop goes down). Do so until the sound of the loop gets distorted ( or to an amount of distortion you can bear ), then make another loop and listen again. Try also different delay time and feedback levels. Like I said before, changing the bias will cut down the frequency range, so, you have to experiment a little bit to find out what's okay for you ( depends i.e. on the instruments and amplifications used ... )
   
   
9. After you've found the best result for you switch off, pull out all plugs and put on the bottom plate again.
   

PS: The two pots up left are finetuners for the modulation. You may experiment with them, too ... The mid left pots function I don't remember, but it may also have to do with the bias/delaytime or feedback level ...

But before you try, MARK THE CURRENT POSITIONS !
I think I needn't to say, why ...