Job Number

0204-50

Equipment type

3-1 Mini System Stereo

Maker + Model #

Aiwa NSX-S111

Made in

Japan

Comments

Found this fault soon after after fixing him the previous fault regards the mains transformer

BAD

1

NO FM tuning

GOOD

1

AM tuning works fine

2

All other function works fine

Full repair description and observations

1

The circuit around the aerial was tested for cracks or dry joints, but everything was normal.

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

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

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

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.  

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