Set your Juno 106 to the following parameters:
Left hand controllers :
DCO: 10 (this will allow the juno to respond to pitch bends).
From left to right:
Rate: 0
Delay: 0
Range: 16'
LFO: 0
PWM: 10
set switch to "MAN"
select square wave
Sub: 4-5
Noise: 0
Freq: 2 (or 1 if you want a fuller sounding bass 303)
Freq: 5
Res: 5
ENV: 0-3
LFO: 0
Kybrd: 0
A: 0
D: 3
S: 3
R: 2.5 (applying a slight release on the sound will create a more convincing
303 "slide".
If you want more details on how to program a TB-303-like pattern on your juno-106 with a midi sequencer, then point your browser at JUNO TRIPS page : http://www.getnet.com/~gofish. You'll get the fulls tips under MASTERTRACK PRO, with full Screenshots and exemples.