Guide Roller Height Adjustment - LG CHASSIS PV-71A Service Manual

MECHANISM ADJUSTMENT

5. Guide Roller Height Adjustment

Purpos e : To regulate the height of the tape so that the bottom of the tape runs along the
tape guide line on the lower drum.
A. Preliminary Adjustment
Test Equipment / Fixture
Post Height Adjusting Driver
*
Hexagonal Wrench or Allen
*
Wrench Phillips screw driver
Adjustment Procedure
1) Perform the precise adjustment(See below B).
2) If the Guide Roller is damaged, loosen the Guide Roller
retaining screw and replace the Guide Roller.
3) Adjust the height of P2, P3 so that TAPE is adjacent to
the guide line.
B. Precise Adjustment
Test Equipment / Fixture
Oscilloscope
*
Alignment Tape
*
Post Height Adjusting
*
Driver
Adjustment Procedure
1) Play an alignment tape after connecting the probe of
the oscilloscope to the RF Envelope Output Test Point
and Head Switching Output Test Point.
2) Tracking Control (in PB mode): Center position (When
this adjustment is performed after the drum assembly
has been replaced, set the tracking control so that the
RF output is maximum.)
3) Height adjustment screw: Flatten the RF waveform.
(Fig. C-5-2)
4) Turn (Move) the tracking control (in the Playback
mode) clockwise and counterclockwise. (Fig. C-5-3))
5) Check that any drop of RF output is uniform at the start
and end of the waveform.
CAUTION
If the adjustment is excessive or insufficient the tape will
jam or fold.
4-19
Test Conditions VCR(VCP) State
Allows a good tape to play
*
normally in spite of a damaged
guide roller.
Test Equipment Connection Points
CH-1: PB RF Envelope
*
CH-2: NTSC: SW 30Hz
*
PAL : SW 25Hz
Head Switching Output
*
Point
RF Envelope Output
*
Point
Guide Roller Height Adjustment
*
screws on the Supply and Take-Up
Guide Rollers.
ADJUSTMENT DIAGRAM
Test Conditions VCR(VCP) State
Play an alignment tape
*
Waveform Diagrams
P2 POST
ADJUSTMENT
P3 POST
ADJUSTMENT
Fig. C-5-2
Tracking control at center
Fig. C-5-3
Connection Diagram
RF ENVELOPE OUTPUT TEST POINT
HEAD SWITCHING OUTPUT TEST
POINT
Adjustment Point
GUIDE ROLLER HEIGHT
ADJUSTMENT SCREW
UPPER FLANGE
GUIDE ROLLER
RETAINING SCREW
Fig. C-5-1
Adjustment Point
Guide Roller Height
*
Adjustment Screws.
Turn the Roller Guide Height
Adjustment Screw slightly
to flatten the waveform.
Turn (Move) the tracking
control to both directions.
OSCILLOSCOPE
CH-1 CH-2