LG RCT689H Service Manual page 106

DECK MECHANISM ADJUSTMENT
7. Adjustment after Drum Assembly (Video Heads)
Purpose of adjustment : To adjust and stabilize the height change, X-distance change, etc
Fixtures and tools used
• Oscilloscope
• Standard test tape
(only for SP)
• Post Height Adjusting
Driver
• Driver (+) Type ø 5
Checking/Adjustment Procedure
1) Play the blank tape (empty tape) and check whether the
guide roller crumbles or wrinkles the tape and adjust it if
necessary.
2) Check that the RF envelope output waveform is flat, and
adjust the height of the guide roller while playing the
standard test tape.
3) Adjust the switching point.
4) Check if the RF envelope output is the maximum when
the tracking control locates at the center. If not maxi-
mum, set up to ensure that RF envelope output becomes
the maximum by turning the (+) type driver (ø 3 ~ ø 4)
on the base A/C groove.
8. Check of Traveling Device after Deck Assembly
8-1. Audio, RF Normalization Time (Locking Time) Check in Play after CUE or REV
Fixtures and tools used
• Oscilloscope
• 6H 3KHz Color Bar
Standard Test tape
• Stop Watch
Checking Procedure
1) Check that the locking time of the RF and Audio wave-
form has fallen within the measuring standard in con-
version of the play mode from the CUE or the REV
mode.
8-2. Check of Tape Curl and Jam Status
Fixtures and tools used
• T-160 Tape
• T-120 Tape
Checking Procedure
1) Check that there is no abnormality of traveling
post status.
2) There must be no abnormal operation of the counter in
depending on the guide roller after assembling the drum.
Connection position
• CH-1: PB RF Envelope
• CH-2: NTSC : SW 30Hz • Play the standard test
PAL:SW 25Hz
• Head switching output
point
• RF Envelope output
point
Measuring standard
• RF Locking Time: Within • CH-1: PB RF Envelope
5 seconds
• Audio Locking Time:
Within 10 seconds
Fixtures and tools used
• There must be no jam or curl at the
first, middle and end position of tape.
4-19
VCR (VCP) status
• Play the blank tape.
tape.
Connection Diagram
RF ENVELOPE OUTPUT POINT
HEAD RF SWITCHING OUTPUT POINT
Waveform
V1/V MAX = 0.7
V1/V MAX = 0.8 V1
RF ENVELOPE OUTPUT
Connection position
• CH-2: Audio output
• RF Envelope output
point
• Audio output jack
2) Perform sections 5 and 6 if it deviates from the
standard.
Fixtures and tools used
• Travel the tape at the position
of its first and end.
if bottom tape folds. There must be no abnormality of
audio signal top tape is damaged.
3) If there is abnormality, perform the adjustment in
sections 4 and 5.
Adjustment position
• Fine adjustment of
guide roller
• Switching Point
• Tracking Preset
• X-distance
OSCILLOSCOPE
CH-1 CH-2
V1 V2
VCR (VCP) status
• Play the 6H 3KHz
Color Bar Standard
Test tape.