Bench Checks; Dc Power Check; Audio Check - Shure T2 Service Manual

Bench Checks

Dc Power
Audio
25C1018 (CC)
Shure T2 Vocal Artist Microphone Transmitter
The tests for power and audio apply to all T2 units. Those involving
the board differ for
RF FCC
this section includes two separate sets of procedures for
n Verify that 9 Vdc (±0.35 Vdc) is present at I+9.0 (on the bottom
of the audio board—see Figure 6, page 33). If this voltage is low,
check it at I133. Trace the circuitry back to the power supply to
see where the loss occurs. Check:
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power switch
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bias on Q105
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L101
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circuit-board ground for 0 V
n If you have a short to ground from 9 V, try isolating different parts
of the circuit. Narrow it down to the
foil shorts, solder bridges, and capacitors that have been
installed backwards.
n Check for 5 Vdc (±0.25 Vdc) at I147. If the correct voltage is not
present, check I+5 (pin 7 of U101). Then check:
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pin 13 of U101 for 9 V
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values of R133, R135, and R137
Note: If you are measuring dc voltages at points where
nals are present, use a 10 kΩ resistor at the probe to prevent
loading the circuit. To remove the
All the steps in this section comprise a methodical way of determin-
ing where the audio signal is being interrupted:
n Check for audio at pin 7 of U102. If it is not present, check that
the dc bias at pins 5, 6, and 7 of U102 is `4.5 Vdc (half the lev-
el of the supply voltage). If the correct voltage is not present:
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Trace the circuitry: this bias derives from the 9 V line through
voltage divider R103 and R105, then through R106 to pin 5.
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Look for open vias (through-hole connections between board
layers), foil shorts, incorrect parts, and bad connections.
n If there is audio at pin 7 of U102 but not at pin 14, check the dc
bias at pins 12 and 13 (`1.8 Vdc) and pin 1 (`3.7 Vdc). If the
correct voltage is not present:
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Trace the circuitry: this dc bias proceeds from pin 9 of U101
through R107 to pin 12 of U102.
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Check (a) the parts in the feedback path from pin 14 to
pin 13, (b) the parts connected to pin 7, and (c) the connec-
tions from U102 to U101.
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-approved and -approved units; hence
ETSI
or audio section. Look for
RF
signal, remove the crystal.
RF
testing.
RF
sig-
RF
Bench Checks