Hitachi VTMX900EUK Service Manual page 33

4. Servo System (AIO1)
Service tasks after replacement of the head drum or EEPROM.
4.1 Setting the gap position (GAP):
Purpose: To determine the correct head switching point
during playback.
Symptom if incorrectly set:
Head switching fault and/or vertical picture flickers.
- Enter the service test program and, whilst step display is
flashing, enter the step number 51, using the numerical keys.
- Insert a test cassette (e.g. 4822 397 30103) with the standard
video signal in the VCR.
- By pressing the SELECT key whilst step 51 is flashing, the
automatic adjustment is triggered and stored in the EEPROM .
TP ADJ. MODE
Service Mode
TAPE MEAS. EQ.
VHS Alignment
Tape
After a correct adjustment, the display shows 1; 0 when incorrect.
Causes of incorrect adjustment :
Incorrect standard video signal.
Scanner fault.
Microprocessor fault.
4.2 "Studio Picture control" adjustment (SPC):
Purpose: Adjustment of the reference level for the SPC.
TP ADJ. MODE
Service Mode
TAPE MEAS. EQ.
SPC Alignment
Tape
- Video signal via Scart or aerial
- Enter the service test program and, whilst the step is flashing,
input the step number 52, using the numerical keys.
- Insert SPC Alignment Tape 4822 397 30268.
- By pressing the SELECT key whilst step 52 is flashing, the
recorder makes a recording in SP mode (approx. 10 sec.) and in
LP mode (approx. 10 sec.), rewinds and carries out a playback
with automatic adjustment.
- After a correct adjustment the display shows 1, and 0 for
incorrect adjustments.
To leave the step press SELECT.
INPUT
Stop
SPEC.
Call up Step 51 of
Service Mode
INPUT
RF or A1- input,
Stop
black picture
without BURST
SPEC.
Call up Step 52 of
Service Mode
5. Audio linear - ( AL)
Service tasks after replacement of coil L5600, IC7004 or the audio
heads:
5.1 Adjusting the erasing frequency [5600]:
Purpose: To set the correct recording erasing frequency.
Symptom, if incorrectly set:
Erasing frequency or its harmonics cause audio faults.
TP ADJ. MODE
connector
L5600
1965
Record E1
pin 5
TAPE MEAS. EQ.
Blank Frequency
Tape Counter
5.3 Adjustment of bias current [3625]:
Purpose: To set the optimum record bias current.
Symptom, if incorrectly set:
If the audio level is too high, the higher frequencies of the
linear sound are too low.
If the level is too low, the higher frequencies are too
strong and sound distortions increase.
TP ADJ.
C2613
R3625
(TP BIAS)
TAPE MEAS. EQ.
AC Millivoltmeter,
Blank
Oszilloskop,
Tape
Video Pattern
Generator
Checking the 'bias' adjustment:
Apply a sine-wave signal with an amplitude of 50mVeff to the
SCART audio input. Record the 1kHz signal and 10kHz signal for 30
seconds each. Play back the recording and check that the amplitude
difference is in the ±3dB range. If this is not the case, correct the
value for the magnetic biasing current. If the treble is too low, the
bias current should be reduced slightly. If the distortion is too great,
the bias current should be increased slightly.
(approximate value: +1V = -1dB Treble).
INPUT
PAL white picture,
with sound on E1
(1kHz or 10kHz)
SPEC.
70kHz
±10kHz
MODE INPUT
PAL white picture,
Record E1 with sound on E1
(1kHz or 10kHz)
SPEC.
14V ±1V
RMS RMS
(70kHz)
2-27
GB