Fostex G24S Service Manual page 27

If the bias leakage level is higher than the spec, it is adjusted to the minimum bias leakage
level by rotating the center core of U21. But before doing this, check the frequency
(lOOKHz ± 0.5KHz) of the master oscillator. To check the oscillator frequency, pull out
the R/P card of the G24S/G16S, and check the frequency at connector J2-8 on the CON ­
NECTOR BOARD PCB Assy.
4.3.6 Erase Current Adjustment
*Caution: Since a multi-turn type pot is used for R209 (ERASE LVL) adjustment, it might
give you a confusion to find out the setting of the maximum erase current level
point.
In order to find out the maximum erase current level point, we would like to sug ­
gest that you rotate the pot clockwise and set to the point where just before the
erase current drastically decreases.
1) In adjusting the erase current, put all the 24/16 tracks in the REC mode.
2) Rotate all the 24/16 tracks of the R209 (ERASE LVL) fully CW.
3) To adjust TRACK 1, for example, hook the hot side of the oscilloscope probe to TP-5
and ground clip of the probe to GND pin.
4) Set the core of T-l (ERASE ADJ) so that voltage at TP-5 reaches the peak level point.
5) Then adjust R209 (ERASE LVL) so that the voltage at TP-5 is 37mVr.m.s. for G24S and
30mVr.m.s. for G16S or the maximum level you can get.
6) Calibrate tracks 2 ~ 24/2 ~ 16 in the same way.
4.3.7 Bias Current Adjustment
*Caution: Since a multi-turn type pot is used for R2 10 (BIAS LVL) adjustment, it might give
you a confusion to find out the setting of the maximum bias current level point.
In order to find out the maximum bias current level point, we would like to sug ­
gest that you rotate the pot clockwise and set to the point where just before the
bias current drastically decreases.
1) Rotate R205 (SYNC CROSSTALK CANCELLER POT) at the center position for all 24/
16 tracks as shown in Fig. 4.17.
TP6 — -» - — R/P A P PCB Assy
R205 |[^
SYNC
X ' TALK
CANCEL
TP1