You need to see if the sound modulates (gets vibrato) using the lever in the first place.
If it does, setting the aftertouch destination to modulation should get you vibrato when you press the key down harder. I presume you’ve tried just pressing the key hard by itself? The force needed may be fairly high. But if the sound doesn’t get vibrato from the lever, aftertouch won’t help.
I think there’s a test routine in the service manual that could check whether it’s working correctly.
To be honest, I found the aftertouch on arrangers not that useful. You are usually playing with both hands, and it can be tough to use accurately (there’s a tendency for it to come in unwanted if you get frisky and play hard) and you have to be careful about pressing hard occasionally with the LH, because the pressure sensor runs the entire length of the action. It doesn’t have a separate sensor for each note.
The G70’s action was quite different to the E80’s, so I can’t comment about the default ‘weight’ of the aftertouch, but it was quite a bit heavier than my G1000, and they also dropped my favorite aftertouch destination, LFO speed. The G70/E80 could only modulate LFO depth. There’s something very organic sounding about a vibrato that changes speed slightly as it’s depth increases. You could slow the factory vibrato speed a hair so you got a light slow vibrato that got faster (slightly!) as it got stronger. Nirvana!
If you’ve gone over p.70 in the E80 manual, you’ve set it up correctly. Perhaps you need to press harder if the sound does engage vibrato with the lever…?
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An arranger is just a tool. What matters is what you build with it..!