Chapter 8 447
IF Section
A5 IF Assembly
Figure 8-14 Faulty LC Pole
30 kHz Resolution Bandwidth Problems
Shape factor too high: Shape factor is the ratio of the 60 dB bandwidth
to the 3 dB bandwidth. Shape factor should be less than 15:1. If one of
the LC poles malfunctions, the shape factor may be the only indication
of the failure. Isolate the non-functioning pole with the IF signature.
Region E of Figure 8-8 on page 440 illustrates the four LC- pole
adjustments. Take several signatures to examine the LC-pole
adjustments. If one of the four sections of Region E is consistently
longer than the others, the corresponding LC pole is faulty.
IF gain compression: FET transistors Q301, Q303, Q700, and Q701 can
deteriorate with age. Measuring less than 0 volts on the FET source
indicates a bad FET.
Bandwidth too wide: Check for contamination on the printed-circuit
board. Clean the board as required.
To Next Page
Loading...
