Akai 4000DS Service Manual page 14

Fig. 15
V. T. V. M.
FREQUENCY
COUNTER
GROUND
3. RECORDING BIAS FREQUENCY
ADJUSTMENT (See Fig. 16)
1) Set the recorder to recording mode.
2) Connect a Frequency counter to points (A) and
(C) in Fig. 16 of the oscillator P.C. Board
(LE-5021) and read the frequency indication.
3) If the bias frequency is 105 kHz ±5%, the bias
frequency is correct.
4) If the bias frequency is incorrect, it can be adjust¬
ed by changing the value of condenser C8 (5600
PF) of the oscillator P.C. Board (LE-5021)
4. RECORDING BIAS VOLTAGE ADJUST¬
MENT (FREQUENCY RESPONSE
ADJUSTMENT) (See Figs. 15, 16)
1) Set the monitor switch to "TAPE" position and
equalizer switch to Vh ips.
2) Connect an Audio Frequency Oscillator to the line
input through an Attenuator and a High Sensiti¬
vity V.T.V.M. to the line output.
3) Load a blank test tape "AKAI 100L" (Fuji S-100)
and set the recorder to "REC" mode.
4) Turn recording level control volume VR-1 and
VR-2 (50k A) to obtain 4 dB V.T.V.M. reading.
5) Under conditions described in Item 4) above,
readjust attenuator so that the line output level is
-16 dB.
6) Record from 40 to 20,000 Hz spot frequencies.
7) Adjust Bias Adjustment semi-fixed condenser C6
(70 PF max.) so that the output of 1,000 Hz and
15,000 Hz frequencies are equal.
8) The bias voltage at this time is around 1 IV A.C.
5. ERASE VOLTAGE
1) Set the recorder to "REC" mode.
2) Connect a V.T.V.M. to points (B) and (C) in Fig.
16 of the oscillator P.C. Board (LE-5021) and read
the V.T.V.M. indication.
3) The Erase Voltage is around 52V A.C.
Fig. 16