EFJohnson 761X, 764X service manual Vhf Adjustments, Preliminary Setup, Pll Adjustment Vhf Models

ADJUSTMENT PROCEDURE

VHF ADJUSTMENTS

in the upper part of the screen is for the currently selected channel.

5.To move the cursor between the parameters on the left side of the bar graph, press the ↑ ↓ arrow keys. To change a parameter, press the ← →, PgUp/PgDn, backspace, or spacebar keys. Refer to the individual adjustment descriptions for more information on the

functions performed using this screen.

6.1.5REPROGRAMMING IF EEPROM IS RE- PLACED OR ERROR OCCURS

When EEPROM IC3 is replaced or if the trans- ceiver displays an error message and beeps, the fol- lowing operation must be performed before making any adjustments.

1.Using the programming software, read (download) the data programmed in an exact same version of the transceiver. Refer to Section 4.4.4 for more information on reading data.

2.Select the MODEL menu and press the down arrow ( ↓ ) key. Type “RESERVE” and press (ENTER).

The “Reserved” indicator should begin flashing in the upper right corner of the screen.

3.Connect the computer to the transceiver that had the EEPROM replaced or is displaying the error (see Figure 4-1). Write the current data to that transceiver.

6.2 PRELIMINARY SETUP

1.Preprogram the transceiver with test channels as described in Section 6.1.2.

2.Connect the computer test setup using the test cable described in Sections 6.1.3 and 6.1.4. Start the program as described.

3.Connect a DC power supply and a 50-ohm, 50-watt antenna load to the transceiver (see Section 6.1.1).

VHF ADJUSTMENTS

6.3 PLL ADJUSTMENT (VHF MODELS)

1.Remove the bottom cover by removing four screws. Connect a DC voltmeter to check point CP1 shown in Figure 6-4.

2.Select the channel on the high end of the band

(Test Ch. 1 - 174.050 MHz). This is done by press- ing the ↑ ↓ arrow keys to highlight “Memory CH” and then pressing the adjust keys (←/→, PgUp/

PgDn, or spacebar/backspace) to select the channel.

3.Key the transmitter using the switch on the test cable and the meter reading should be 4.3 volts. If this voltage is significantly different, adjust L14 (it may be necessary to remove the VCO shield).

4.Unkey the transmitter and the meter reading in the receive mode should be 3.3 – 4.3 volts.

5.Select the channel on the low end of the band (Test Ch. 2 - 146.050 MHz). The meter reading should be 0.9 – 1.9 volt in both the transmit and receive modes. Replace the bottom cover.

6.4TRANSMITTER ADJUSTMENTS (VHF MODELS)

6.4.1 REFERENCE FREQUENCY

1.Select the channel on the high end of the band (Test Ch. 1 - 174.050 MHz).

2.Scroll down to “TXF SET” on the screen and press (Enter). Monitor the transmit signal with a fre- quency counter and key the transmitter using the test cable switch.

3.Adjust for the displayed frequency by pressing the computer adjust keys. Unkey the transmitter.

November 1998
Part No. 001-7600-001	6-4