ELECTRONICS CORNER
My Repair Jobs
Job Number |
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0201-38 |
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Equipment type |
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Car Stereo (Radio+Cassette) |
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Maker + Model # |
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Made in |
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Comments |
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Could not find fault, and continued again to work on
it 3 months later. After fixing it, Louis said that I can keep the radio
since his friend is not in |
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BAD |
1 |
All bands of radio does
not play |
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GOOD |
1 |
Powers up |
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2 |
Cassette functions well,
and good sound is produced |
Full repair description and observations |
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1 |
Initially the radio band
select swtiches were investigated for a probable jamming, dry joint, or
mechanical fault, but there was nothing obvious as such. |
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2 |
The circuit was very tedious and the amp IC (SP 800 by SGS) could not
be found on the internet for a datasheet. Various attempts and guess work was
done to find a faulty component but everything seemed to be good |
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3 |
After several weeks, I
decided to buy the 4 main IC that the tuner had (except the amp IC) perhaps
one of these went open. They were purchased from |
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4 |
The power supply for the
FM tuning IC, (just replaced) was found on the datasheet that it should be
12V, but on the circuit I had 0.1V. I followed the power supply track on the
circuit and finally I found a dry joint at resistor in series with the Vcc in
of the IC. |
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5 |
When the dry joint was
fixed, all bands of the radio became operative and hence the fault was fixed. |
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6 |
Finally a general
service was given, which included replacing faulty light bulbs, cleaning the
head and pinch roller and greasing mechanism of the cassette unt, cleaning
user potentiometers (eg volume) and switches. |
Repair summary |
OPEN CIRCUIT AT VCC OF THE
TUNER Ics DUE TO A DRY JOINT |
Precautions, fouls and advises |
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1 |
Before buying Ics as an
action of guess due to a clueless fault, check the function of the IC from
the internet. For example in this case, the noise canceller IC could have
been avoided. |
1 |
When the cassette is on
operation the voltage is given to the pre amp, while when the radio is used,
the preamp is switched off. Hence the Pre-Amp is used only for the playback
of cassette. |
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2 |
The following IC.s were present in the circuit: LA 1130 - AM tuning IC LA 1140 - FM Tuning IC LA 2110 - Noise canceller TA 7325P – Audio Pre-Amplifier LA 3376 - ??
SP800 - Audio Power Amplifier |