If mute pin 8 reads near 0 volts, change IC.
If mute pin 8 of any/all output IC’s reads close to –15 volts, recheck above
results and signal trace PCB. If the unit measures positive or close to zero the
unit is detecting a fault or there exists a problem with the fault detection
circuitry. Signal and voltage trace accordingly using circuit description.
Low output power problems
Verify proper level input at pin 10 of output IC’s
If level ok, replace IC (U1, U2—Low Frequency amplifiers
U3—High Frequency amplifier)
If not ok, signal trace back to fault using circuit descriptions, repair and
continue check out
No power On LED indicator operation
Verify -15 volt at Q3 and leg of R47
Verify -2V on opposite end of R47
If absent, change LED
No input signal indication
Verify operating voltage of ±15V on U3 of input/output PCB
Verify input signals from the low and high frequency outputs at D6 and D7
Verify C55 charging and discharging.
Verify threshold voltages by inputting external voltage to inverting pin of U3
on Input/output PCB
At 0 volts--no illumination
Below 0 volts to -3.1 volts—green illumination
At/below -3.1Volts—red illumination
If above is ok, replace IC U3 (TLO74)
No microphone LED indication
Verify 15 Volts at junction of R57/R54
Verify audio ground on cathode of DS1
Verify LED element operation. If defective replace LED.
Verify continuity of SW2 contacts
To Next Page
Loading...
Need help?
General