Shure T1 Body-Pack Transmitters
18Bench Checks
25C1016 (CC)
n Check the bias voltage (`4 Vdc) on pins 8, 9, and 10 of U102. If
the correct voltage is not present:
S Make sure the Mute switch is set to “On.”
S Trace the bias circuit from the 5 V line through R104 to
pin 10 of U102.
S Check the values in the feedback path from pin 8 to pin 9 of
U102, and the path to Q104 and pin 16 of U101.
Frequency Problem
n Make sure the RF carrier is at least 10 dB higher than the spuri-
ous emissions, to allow the frequency counter to lock on.
n Check L209 for the proper group and make sure its core is not
cracked.
n Make sure the crystal (Y201) has the correct frequency.
n Check the dc bias for Q201 against the readings of a unit known
to be operating correctly.
n Make sure that D201 is the correct varactor and has 5 Vdc on its
cathode.
n Check the parts and values of the oscillator circuit (from
TP3 to
TP5).
n Look for shorts and opens.
Low Output Power
n Check the carrier output power after the oscillator stage (TP5). If
there is no signal, refer to the preceding subsection, “Frequency
Problem.”
The remaining steps perform basically similar diagnostics for each of
the three
RF stages:
n Stage 1: Make sure that rotating C217 360 degrees in either di-
rection produces two separate peaks in the carrier output ampli-
tude. If there is only one peak, check the color (value) of C217
and the values of L205, C225, C234, L202, and C233. Check
the bias on Q201. Lastly, replace Q201.
n Stage 2: Make sure that rotating C215 360 degrees in either di-
rection produces two separate peaks in the carrier output ampli-
tude. If there is only one peak, check the color (value) of C215
and the values of L204, C237, C236, L207, C235, C222, and
C226. Check the bias on Q203. Lastly, replace Q203.
n Stage 3: Check the dc bias on Q204 and the values of all the
parts from the base of Q204 to
TP4. Lastly, replace Q204.
n If the power is slightly low and the spurious levels are high,
check for wrong or open coils at L202, L207, and L206.
