Shure UC1L Service Manual page 24

Shure UC1 Body-Pack UHF Transmitter
Low Rf Output Power
Excessive Current Drain
Deviation Problems
Bench Checks
Check the polarity of the low-pass filters U107, U108, and U109.
(Pin 1 is marked with a dash.)
Check for missing ground connections.
Verify the VCO output power at R128 and U104, pin 8.
Check the dc level at the VCO Vcc pin.
Isolate the VCO from the rest of the circuit by removing R127,
R128, and C134. The carrier frequency will no longer be locked,
but the output power from the VCO should be approximately
0 dBm.
If the power out of the VCO is still low, the VCO is bad.
Replace the rf board.
Verify the dc bias of Q102 and Q104. Verify the rf mute signal
changes from +5 Vdc at power up and power down, to 0 Vdc
during normal operation. If Q103 and Q105 are not saturated
during normal operation, the rf power at the antenna port will be
attenuated by about 45 dB.
Isolate components starting from the antenna port and working
back to the rf power amp.
Remove the low-pass filter and check the power OUT of the
amplifier.
Check the values of the output matching network for Q102 and
Q104, C258, L206, and C256. Look for open coils.
Check the values of the bypass capacitors.
As a last resort, replace the transistors, Q102 and Q104.
Isolate different sections of the circuit; rf, audio, and digital.
Look for reversed polarity capacitors or wrong resistor values.
If R149 cannot be adjusted to obtain the desired deviation, try to
isolate the problem to the audio or rf section.
Check the value of R149. To check the rf section, set the trans-
mitter frequency to 800 MHz and verify that the tuning voltage of
the VCO (U104, pin 5) is approximately 3 Vdc.
24 25A1043 (RI)