Cleaning And Oiling - JVC CD-1740 Service Manual

Auto-stop check-ups and adjustments
1. Mechanism section
When the magnet keeps stopping, and the cassette is
automatically stopped, it is necessary to check the
followings;
1. Check to see whether the belt is broken off.
2. Check to see whether the magnet-pulley and/or
magnet is taken off.
3. Check to see whether the lead switch is switched off.
2. Checking circuits for operation
When the rewinding operation approaches the end, the
ejection of the cassette tends to occur.
For this reason, it is necessary to check the control circuits
for operation.
Trouble Shooting
Electrical circuit
1. Playback tone quality is poor
1) Check the record/playback head for dust.
2) Check the record/playback head for wear.
If worn excessively, the loss of treble response will
result.
3) Check wiring for a short-circuit.
Check each transistor for condition.
4) Check the noise reduction circuit for condition.
(This check-up should be made by turning on and off
the switch off the Dolby NR.)
2. Recording tone quality is poor
The playback tone quality of a recorded tape such as the
audition tape is good, but the recording by this unit
produces poor tone quality. In this case, the unit should be
checked in the following manner.
Cleaning and Oiling
1. Cleaning
Clean the contact surfaces of the record/playback head,
capstan and pinch roller with the tape.
If the head is dirty, tone quality will be greatly impaired, or
erasure will be imperfect.
Clean them with a cloth moistened with alcohol, benzine,
or trichloroethylene.
Keep the cabinet free from these chemicals, or the surface
will be dissolved.
2. Oiling
Feed one or two drops of machine oil to the rewind roller
shaft, pinch roller shaft and magnet pully shaft once or
twice a year under normal conditions of use.
Avoid oiling them excessively, or rotation may become
irregular because of oil splashes.
1) By monitoring a music while recording, check the tone
quality.
2) If found poor, check the wiring of the recording system
for a broken wire and short-circuit.
Check transistor for function by measuring voltage.
3) If no irregalarity is found, check the recording bias
current. Also check the oscillation circuit.
4) Check the noise reducing circuit for operation.
3. For other failures, check the unit in the same manner as
other amplifiers.
Mechanism section
If wow and flutter increase, check the following points.
If there is defect in revolving parts, the wow and flutter
generated will increase in propotion to the number of
revolutions.
Play a 3000Hz test tape, and defective part can be detected
from the sound.
Capstan
Flywheel turns heavily.
(shaft seisure, thrust play etc.)
Pinch roller
or dust)
Angle is incorrect.
Pressure is incorrect.
Capstan belt
Back tension
is too strong.
Motor
Take-up lever arm
Capstan shaft has excessive run-out.
Rough rotation (Deformation scratches,
Back tension is irregular, or back tension
Replace flywheel.
Adjust plastic screw with flywheel holder.
Replace pinch roller.
Clean adjust so that it is parallel to
capstan.
Adjust spring.
Belt has undue run-out. Replace take-up belt.
Belt is dirty or slippery. Clean or replace.
Replace supply disc.
Replace back tension spring (under
supply disc), or apply silicon grease.
Motor shaft has undue run-out. Replace motor.
Motor pulley is oily and dusty. Clean motor pulley.
Pulley has deflection. Replace take-up idler arm.
Pulley is stuck.
CD-1740/A/B/E/U
Ota No. 4133