Distortion Check; Frequency Problem; Low Output Power - Shure T2 Service Manual

Shure T2 Vocal Artist Microphone Transmitter
Distortion

Frequency Problem:

Low Output Power: FCC-Approved Units
Bench Checks
n Check the connections from pin 14 of U102 to the next stage, to
the limiter (Q103), and to pin 15 of U101.
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 Mic 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.
n Make sure the analyzer's 400 Hz high-pass and 30 kHz low-
pass filters are pressed in.
n Pin 9 of U101 should read `1.8 Vdc.
n As you turn R130, the dc level on its wiper should change from
`1.5 V to 3.5 V. If it does not, check R129, C125, R130, R141,
R140, R126, and the parts tied to pin 9 of U101.
n Check the audio level.
n Lastly, replace D201 and Y201.
-Approved Units
FCC
n Make sure the
RF
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 I218 to
I230).
n Look for shorts and opens.
For these checks, terminate the transmitter's output with a 50 Ω load
between I210 and ground. If you have interconnected the audio and
boards for testing, temporarily remove C240 to disconnect the battery
antenna.
n Check the carrier output power after the oscillator stage (I230).
If there is no signal, refer to the preceding subsection, "Frequen-
cy Problem."
The remaining steps perform basically similar diagnostics for each of
the three stages:
RF
24
carrier is at least 10 dB higher than the spuri-
RF
25C1018 (CC)