Crown Broadcast Low Power Trouble Shooting Guide

Transmitter does not light up

·         Check Circuit Breaker on back of unit

·         Check fuse

·         If front panel was not functioning check ribbon cable connection

·         Check unregulated voltage (white blue wire on voltage regulator)

·         Check (+) and (-) 12 volts. On voltage regulator board

- Output of U705

RF Power problem

·         Check unregulated voltage

- unit makes power but output is low

·         Check that power out matches front panel

·         Adjust RF level control on front panel

- if there is a “Flat Spot” on the RF level control turn control counter clockwise to see where power starts to drop.

> Turn RF level control full clockwise

* Check RF Voltage at;

- Input of Q900 our driver should be about 17 V P - P

- Output at 40V P-P

No Power no PADC

·         Check pre-driver U900

·         Check Driver Stage

- Driver Bias FM30 = 3.5V at non RF side of R904

- Driver Bias FM100 & 250 1.75V at non RF side of R904

- If able to connect to a wattmeter

* FM30                       >30 Watts

* FM100-250              10 Watts

·         Check PA Module

- Check that RF is getting to Q1101 on PA

- Check our BNC on input board for RF shorts

·         PA DC Fault Flashing

- RF Level full counter clockwise

- Open low pass filter

- Faulty Antenna

- R34 (power setting) full counter clockwise

- R12 Current limit is too low

* Measure at the board site of R13

 FM30            =          0.265VDC

 FM100          =          0.565VDC

 FM250          =          0.815VDC

 FM500          =          1.75VDC

Audio

FM30—27 watts

FM100- <50watts

FM250 < 197 watts 

Max– Q900 could be bad.

No Power no PADC

·         Load down the power regulator

- 10-ohm—220 Watt Resister

- Turn Carrier on and you should see PADC and PA amps

> If no voltage

* Replace U1, U2, Q801 and Q804

(all will have unregulated voltage on them)

·         Check driver and voltage on voltage regulator board 18-24 V DC

- No voltage

> Check the cathode side of D2-703

* If no voltage replace U801,802-Q801

·         No Voltage

- Check Q704, base 18V transmitter 19 collector 19

·         Turn on Carrier

·         Measure the outboard side of R13

- Turn current limit POT R12 to the following for:

                        > FM30           .265VDC

                        > FM100         .565VDC

                        > FM250         .815VDC

                        > FM500         1.75VDC

·         Adjust R67 SWR for 1.03 on front panel

·         Turn carrier on

·         With a wattmeter in-line adjust R34 power set to read

                        > FM30           33 watts

                        > FM100         110 watts

                        > FM250         275 watts

                        > FM500         550 watts

·         Adjust R72 power calibration to read the same as the wattmeter