Korg Poly-800II Service Manual page 29

2. FEEDBACK TIME Verification, Adjustment
1) Select program No. 15.
2) Connect on oscilloscope (AC, 50mV/div, 0.1 sec/div) to TP1.
3) Play C3 key, and check that the envelope of the waveform
(from peak of waveform to decay) is 600msec ± 50msec.
(Fig-2)
4) Adjust VR 1 if necessary
AC50m/m
O.isec
600msec
Fig-2
3. ANALOG COMPANDER NE572 Verification, Adjustment
1) Select program No. 16.
2) Connect on oscilloscope (AC 50mV/div, 0.1 sec/div) to TP1.
(Connect ground to TP2)
3) Play C3 key, and check on the oscilloscope that visible
waveforms are formed which are unifprm in size and shape.
Note:
Although this can be abjusted via VR2, because it is fixed at
a fully couterclockwise position, so it should not be turned.