Harris DX 25U Technical Manual Download Page 70

Page: 70 / 274

i. To turn on an RF amplifier, depress the LOW power button

and note that the PA Power supply voltage comes up as
indicated on the front panel multimeter but no RF power
or PA current is indicated.

j. Depress the RAISE button to illuminate the green LED

indicator on RF33.

k. Measure the peak-to-peak drive level on the scope moni-

toring the drive.

l. The waveform should measure from 21.0 to 25.0 Vp-p and

it should be centered on the 0.0 VDC line of the scope.

m. If the waveform falls totally below the 0.0 VDC line of the

scope, the Step 1 RF amplifier is turned “OFF”. See
Figures 5-3 and 5-4 for drive waveforms.

n. Record the reading on the RF Multimeter position for

DRIVER D8A and D8B. The Driver Supply Regulator will
be set back to this voltage once the overloads are adjusted.

5.6.7.2.2

Underdrive Overload: R67

To adjust Underdrive overload R67, the drive must be reduced to
18.0 Vp-p.

a. To reduce the drive, depress the OFF button and allow the

PA Voltage to discharge.

b. Open the interlocked door inside the Driver Compartment

and remove Driver Module D1.

c. Remove both supply voltage fuses and re-insert the RF

amplifier into position.

d. Close the interlocked door and depress the LOW button.

e. Driver D8A voltage will be higher than normal and there

may be a voltage reading on the D8B position.

f. Measure the drive level at RF33 on the scope. If the drive

level is above 18.0 Vp-p, repeat the above procedure for
Driver Module D2.

g. Continue removing fuses from Driver Modules D3

through D5 until the level decreases to 18.0 Vp-p.

h. When a level of 18.0 Vp-p is achieved, adjust R67 on the

LED Board until the transmitter turns OFF and displays an
Underdrive Fault on the ColorStat™ panel.

i. Replace all fuses removed from the Driver Modules to

restore the Driver stage to the correct output.

j. Press the LOW power button. The transmitter PA Power

supply should energize, there should be no power out, and
the drive level to the PA Modules should be the same as
measured originally.

5.6.7.2.3

Overdrive Overload: R41

To adjust the Overdrive Overload, the RF drive must be increased
to 26.0 Vp-p.

a. To adjust the Overdrive overload, place switch S1 on the

Driver Supply Regulator in the OPEN LOOP position and

note the voltage of D8A and D8B on the RF MULTIME-
TER.

b. Adjust R2 on the Driver Supply Regulator clockwise (CW)

until the drive level reaches 26.0 Vp-p. If the voltage will
not reach 26.0 Vp-p, place S1 on the Driver Encoder/Temp
Sense Board to the ON position. This will turn on the spare
Driver Module D6.

c. Adjust the Overdrive overload R41 on the LED Board until

the transmitter turns OFF and an Overdrive overload is
indicated on the ColorStat™ panel.

d. Turn the OPEN LOOP adjustment R2 two turns CCW and

return S1 on the Driver Encoder/Temp Sense Board to the
OFF position if moved.

e. Depress the LOW power button. The PA Power supply

should energize and there should be no RF output from the
transmitter.

f. Readjust R2 to the same voltage as earlier recorded on the

multimeter DRIVER D8A and place S1 in the CLOSED
LOOP position. The RF drive level should be the same as
first noted.

g. Remove the 10x scope probe from the RF amplifier.

h. Turn the transmitter OFF and note that PA Voltage de-

creases to zero on the multimeter.

i. Remove primary AC power from the transmitter at the

main breaker.

WARNING

ENSURE ALL PRIMARY AC VOLTAGE HAS BEEN REMOVED
FROM TRANSMITTER AND A GROUNDING STICK IS USED TO
GROUND ALL POINTS WHERE AC OR RF POWER HAS BEEN
APPLIED BEFORE PROCEEDING WITH THE FOLLOWING PRO-
CEDURE.

j. Remove the Driver Compartment and RF Amp Compart-

ment rear access panels and replace all the PA Power
Supply fuses.

k. Replace all panels and restore primary AC power to the

transmitter at the main breaker.

5.6.7.3

Peak Current Overload: R68

a. Turn the PEAK current overload R68 fully CCW.

b. Operate the transmitter at 25 kW and modulate at 100%

with a 20 Hz sine wave. Increase the audio level 1.4 dB.
Adjust the PEAK current overload R68 for an overcurrent
trip.

5.6.7.4

Average Current Overload: R42

a. Operate the transmitter at 25 kW and modulate with 20 Hz