ELECTRONICS CORNER
My Repair Jobs
Job Number |
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0204-50 |
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Equipment type |
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3-1 Mini System Stereo |
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Maker + Model # |
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Aiwa NSX-S111 |
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Made in |
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Comments |
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Found this fault soon after after fixing him the
previous fault regards the mains transformer |
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Symptoms observed
BAD |
1 |
NO FM tuning |
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GOOD |
1 |
AM tuning works fine |
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2 |
All other function works
fine |
Repair
notes
Full repair description and observations |
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1 |
The circuit around the
aerial was tested for cracks or dry joints, but everything was normal. |
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2 |
The RF signal from aerial
was followed on board and it was found to pass through a transistor, then a
10.7 band pass filter and finally into FM IF input pin 1 of the IC LA 1837 |
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3 |
At first the IC was the
first suspect, but on viewing the datasheet of the IC, it was found that this
IC handles AM tuing and output and since it is very difficult that only part
of the IC gets faulty, it was decided that the IC was not the problem |
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4 |
I checked the band pass
ceramic filter and the input and earth are shorted, however on desoldering
and testing the filter out of the circuit, it was not short! The short came
from somewhere else in the circuit |
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5 |
It was found that the
short was in a small board placed perpendicular to the board. Initally it
seemed a simple board with few coils, but on desoldering, it was found that
it had various surface mount components n the other sides. It was found that
the earth and its RF output were shorted. |
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6 |
This was replaced (after
1 month waiting for part) and the FM tuning returned operating back to normal |
Repair summary |
FM TUNER BOARD SHORT CIRCUIT |