Service manual

Shure LX2 Hand-Held Transmitter
30
Bench Checks
25D1006 (CG)
Bench Checks
Power Input Problem
Dc Input
n Verify that 9.0 Vdc ± 0.35 Vdc is present at the 9.0 Vdc test
point (U101, pin 13). If this voltage is low, check N33.
n Check the power switch bias on Q105 and L101.
n Make sure the circuit board ground is 0.0 Vdc.
n If there is a short from 9.0 Vdc to ground, try to isolate different
parts of the circuit; narrow it down to the rf or audio section.
n Look for foil shorts, solder bridges, and capacitors that have
been installed backwards.
n Check for 5.0 Vdc ± 0.25 Vdc at N147. If voltage is low, check
the +5.0 Vdc test point (U101, pin 7). If the voltage is not cor-
rect, check U101, pin 13 for 9.0 Vdc; also check the values of
R133, R135, and R137.
n If dc voltages are being measured at points that have rf present,
use a 10 kΩ resistor at the probe to prevent loading the circuit.
Excessive Current Drain
Domestic (FCC/IC)
n Readjust C216 for lower current drain while maintaining output
power to specification.
n If current drain is still excessive, there may be a short, wrong
resistor values, or a defective capacitor.
n Make sure that R219 is the correct value for the frequency group.
n Last of all, try changing Q204.
Euro (ETSI)
n Readjust C226 for lower current drain while maintaining output
power to specification.
n If current drain is still excessive, there may be a short, wrong
resistor values, or a defective capacitor.
n Make sure that R218 is the correct value for the frequency group.
n Last of all, try changing Q204.