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Bench Checks
Power Supply
Channel EQ
25A1041 (RA)
Shure AMS8100 Automatic Microphone Mixer
General
Check to see if F901 is not blown. If it is blown, check the unit
to see why it blew. If nothing can be seen, replace F901 and
slowly bring the ac power up with a Variac while monitoring the
supply rails. If any of the supplies appear shorted, remove pow-
er and do more troubleshooting of the circuitry.
Check for about 40 Vp–p at the secondary of T901. The signal
should look like a sine wave with flattened peaks. If it is not
there, suspect T901, SW903, F901, the wires to the ac power
connector, the ac power connector, or the printed circuit board.
15 Vdc Supply
Check for about +20 Vdc across C954 and across C953. This
signal will have a ripple on it. If this voltage is not there, there
may be a short in subsequent circuitry, the diodes feeding these
capacitors may be open, or the capacitors themselves may be
shorted.
Check for 8.2 Vdc across Z903 and Z902. If not there, the
zener diodes may be shorted.
Check for 7.7 Vdc at Q932's emitter and –7.7 Vdc at Q924's
emitter. If not there, Q932 or Q924 may be bad.
Check for about 1.2 Vdc across the base emitter of Q919 and
Q915. If not there, Q919 may be bad.
Apply a signal to the mic/line input.
Check for the signal at U801 pin 1.
Check for the signal on the other side of C834.
Check for the signal at U809 pin 7.
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Bench Checks
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