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AM-FM Stereo Tuner KT-1100 (TRIO-Kenwood)

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[What was happen?] [Cause] [Repair]

This tuner are using the double conversion system to gain high S/N ratio at the pulse count detector.

Fig.1 Block diagram of 1st IF - 2nd Mix - 2nd IF - PCD of KT-1100

Fig.2 1st IF(10.7MHz) - 2nd Mix - 2nd IF(1.96MHz)

Fig.1 shows the block diagram of 1st IF - 2nd Mix - 2nd IF - PCD. And Fig.2 shows the pwb aroud Fig1. The 1st IF frequency is 10.7MHz and the 2nd IF is 1.96MHz. After the 1st IF amplifire and filters, the signal goes into the custom IC ( TR7020;IC5 ), which is consist of the 1st IF amp, quadrature detector for the servo lock AFC system, 2nd local oscillator and 2nd mixer.

The 1st IF input ( pin-17 )to the quadrature detector output ( pin-10 ) are OK, but after the 2nd mix output ( pin-7 ), there is no signal.

There is no osccilation signal at 2nd local osccilator pin ( pin-9). Only +5V DC signal through L5 from vcc line is at the pin-9. L5 is 2nd local osc tunk inductor, and it seems to be L5 short or built in capacitor leakage or built in capacitor open failure.So, I removed L5 from the pwb.

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