ELECTRONICS CORNER
My Repair Jobs
Job Number |
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0204-48 |
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Equipment type |
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Long Play, Cassette recorder and tuner stereo
amplifier |
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Maker + Model # |
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National Panasonic SG-1070L |
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Made in |
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Comments |
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Very old, but in good state. It seems that this had
the first prototypes of STK power amp integrated circuits. |
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BAD |
1 |
Cassette and long play sound noisy & low
definition |
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2 |
Long play arm moves
rapidly without playing music |
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3 |
FF and REW of cassette part sloppy and slow |
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4 |
Volume and balance pots noisy on adjusting |
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GOOD |
1 |
Powers up, and good sound output |
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2 |
Tuner sections works perfect |
Full repair description and observations |
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1 |
The arm used to move fast because of the
wrong alignment of the needle. It has to be perfectely perpendicular to the
longplay. The needle was repalced and fitted in place and the moving arm
fault and the noisy sound from the long play were fixed |
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2 |
The cassette heads were thoroughly cleaner
with iso propyl alcohol, and the sound on the cassette unit improved very
much |
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3 |
The rewind and fastforward problem was due
to an old weared audio belt. Actually there was 2
belts, one used to drive the play/ff/rew mechanism from the motor, and one to
make the counter to operate. Both belts were replaced. This meant to dismount
the cassette compartment since the former belt could not be reached. |
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4 |
The volume noise problems was arranged by
the usuall contact spray servicing to the corresponding potentiometers |
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5 |
Further servicing, such as greasing the
motors and cleaning the deck were further performed. |
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6 |
The unit was mounted back carefully and gave
a final cleanup to the outer casing. |
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7 |
On testing
the turntable, it was noted that the sound output on the longPlay section was
very low, while ok on the Tuner and cassette section. |
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8 |
On applying
an external sound output to the connection where the LP sound input is fed,
the sound was amplified normally, hence the fault is in the pickup of the
sound from the needle. |
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9 |
Since the
needle was new, the fault is in the ceramic cartridge, and a replacement
could not be found yet. On examining other cartridges, it was noted that
probably the fault was due the fact that the cartridge had a missing part – a
connection between the needle and the ceramic pickups. When such a part was
home made with plastic-rubber material, the sound improved slightly! |
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10 |
Attempts to find a
replacement cartridge from local shops or the internet failed! |
Repair summary |
1) Wrong needle adjustment 2) Old needle diamond 3) Worn and old rubber belts in the cassette
unit 4) Dirty volume/balance potentiometers 5) Parts missing from the ceramic cartridge
pickup. |