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DR-7 DIGITAL READOUT

The DR-7 provides two major functions for the TR-7 - full receiver coverage from 1.8-30 MHz and digital frequency display. The two sections are completely independent. A failure in one section will usually not affect the other. A careful observation of the symptoms and a few measurements will isolate the fault to a major section. See table 4-l before removing DR-7. Refer to figure 4-2 for the parts location and figure 4-3 for the schematic. 

All waveforms on the schematic are taken with the TR-7 tuned to 1.9500 MHz. All waveforms are taken with the oscilloscope set to AC trigger on the first edge shown on the schematic, i.e.: rising or falling edge. An oscilloscope with at least a 100 MHz bandwidth is required to faithfully reproduce some signals. Some signals, especially in the counter and display section, may be displayed with jitter when viewed on an oscilloscope without trigger hold-off. All levels are 0V and 5V high unless noted otherwise.

Section 4-1.1 contains the detailed theory of operation for the full coverage section and 4-1.2 for the digital frequency display. U9001 (6) refers to I.C. #9001, pin 6. Ground and supply connections are #7 and #14 for 14 pin I.C.‘s, #8 and #16 for 16 pin I.C.‘s, and #12 and #24 for 24 pin I.C.‘s, unless noted otherwise.

If trouble is suspected with the full coverage section, remove the DR-7 and replace it with the Jumper Board for verification. If a component must be removed, USE CARE. Wicking braid and a low wattage, grounded soldering iron are recommended for component removal.

LED displays are matched for brightness. If a failure is determined to be in the display, replacement of both is advised. The recommended procedure to remove the display is to cut the connector pins close to the DR-7 P.C. Board. Remove the pins and clear the holes of solder. To replace the display, solder the displays to a new connector. The displays should be flush with the connector. The two digit and four digit displays are spaced apart one pin. Insert the display and connector assembly into the DR-7 board. Space the connector body .l inch (.254 cm) using a drill bit or other spacer. Solder the connector to the DR-7 board and remove the spacer

TROUBLESHOOTING GUIDE

FULL COVERAGE SECTION

The major functions of the full coverage section are to take the synthesizer load number provided by the digital control board and increment or decrement the load number with the UP or DOWN front panel switches within the limits of the input low pass and high pass filters and to enable the transmitter on the amateur bands. When the bandswitch is changed from one band to another, U9002 (1) is momentarily grounded via the wire going to the high pass filter module. If the AUX PROGRAM switch is in NORM, U9002 (3) will go high and trigger U9004, a one shot. The negative pulse out of the one shot will cause U9002 (4) to go high, latching the BCD load number present at pins 2/ 41 through 2/48 into the programmable up-down counters U9005 and U9006. The one shot insures that the data from the band switch is valid before latching the number. In AUX PROGRAM switch positions l-8 U9002 (6) is held low, causing U9002 (4) to stay high. This allows any load number at the counter inputs to be fed directly to the outputs. The outputs of the counters are buffered by the high current drivers U9007 and U9008 and applied to the divide by N inputs of the translator board. When the UP or DOWN pushbutton is depressed, a negative pulse is generated at the output of one shot U9004 (7) and applied to the clock inputs of the counters. When the DOWN pushbutton is depressed U9002 (11) remains low, the counters will decrement by one and the VCO frequency will increase. The load number is fed to the inputs of READ ONLY MEMORY U9003. When a load number corresponding to a band edge is programmed, U9003 (12) and/or U9003 (11) will go low and disable the UP or DOWN latches. Refer to paragraph 1-3.3 to determine the proper load number for a particular 500 kHz segment.

COUNTER SECTION

The counter circuit can be divided into three major sections: the time base divider, the counter, and the display. The time base divider generates the signals required to gate the input signal into the counter, store the contents of the counters, and control the multiplexed information to the display section. The display section decodes and buffers the multiplexed information from the counter section and drives the LED display.

The TIME BASE DIVIDER is comprised of U9014, U9015, U9019, U9022, U9026, U9028 and U9016. The 500 kHz synthesizer reference signal is divided by 5 by U9014 producing 10 micro S pulses. The 10 micro Sec pulses are applied to the divide by 10,000 circuit consisting of U9017, U9019, and U9022, and to flip/flop U9026. After 100 mS, U9016 (13) will go low. At the next pulse from U9014, U9026 (1) will go low and U9026 (2) and U9015 (2) will go high, generating a strobe pulse at U9015 (10). On the second pulse from U9014 after the strobe pulse, a reset/load pulse is generated at U9016 (3). On the second pulse from U9014 after the reset pulse, a time base reset pulse is generated at U9016 (1). This pulse resets the dividers and sets U9026 (13) high. On the next pulse, U9026 (1) goes high and the sequence starts again. During the 100 mS gate time, the BCD output of U9019 is fed to 1 of 10 decoder U9028. The outputs of U9028 are used to multiplex the BCD information stored in the latches to the display section.

The COUNTER CIRCUIT consists of input amplifiers U9009 and U901 0, gating circuits U9011 and U9012, and counting circuits U9013, U90 17 through U9021, U9023 through U9025, U9027, and U9030. The VCO signal is amplified by U90 10. The external input signal is amplified by U9009. U9011 selects which signal is applied to the gate circuit. When U9012 (7) goes high, U9012 ( 3) will go low on the next rising edge of the selected input signal allowing the signal to be passed to decade divider U9013. The outputs of U9013 are buffered and applied to Q9002, which amplifies the ECL level signal to a TTL level. The TTL signal is applied to decade counter U9017 and  then to U9019. The output of U9019 is applied to the programmable decade counter chain U9020, U9023, U9024, and U9027. The outputs of all of the counters feed latches. At the end of the gate time the BCD information is stored in latches U9018, U9021, and U9025 by the strobe signal from the time base divider section. After the strobe signal, the counters are either reset to all zeroes or loaded with an offset number by the reset/load pulse. When the DR-7 is operating in the NORMAL mode, the reset/load pulse is applied to pin 1 of the programmable counters and U9016 (5). U9016 (6) is grounded by the NORM/EXT switch preventing the load/reset pulse from resetting the counters. The counters will be preset to 5195, which will subtract the 48.05 MHz First IF from the VCO frequency. In the EXT mode the reset/load pulse is applied to both pin 1 and pin 9 of the programmable counters setting them to zero. When operating in the EXT mode and the input frequency exceeds 99.9999 MHz, U9030 (13) will go high and U9030 (1) will be latched high by the strobe pulse. When the STORE pushbutton is depressed, the strobed pulse is grounded and the information in the latches is not updated by the counters.

The DISPLAY SECTION is comprised of U9028, U9029, U9031, U9032, Q9005 through Q9013, and the LED display. When U9028 (2) goes low, the BCD information stored in latch U9025B is applied to the BCD to 7-segment decoder U9029.The outputs of U9029 are applied to U9032. The outputs of U9032 sink current from the common anode LED display. At the same time, the outputs of U9025B are enabled, Q9005 is turned on by U9028 (2) supplying current to the left-most digit of the display. After Dl has been lit for 100 mS, U9028 (2) will go high and U9028 (3) will go low, turning on Q9006 and enabling the information stored in U9028A to be decoded and applied to the cathodes. Each digit will be enabled sequentially for 100 mili S at a 1 kHz rate. Q9012 is turned on at D5 to illuminate the decimal point. If Dl is zero, U9029 (4), U9031 (1) and, if the counter has not exceeded 99.9999 MHz, U9029 (5) will go low and the leading zero will be blanked. U9031 (1) will remain low until a number other than BCD "0" is applied to the inputs of U9029. When the counter is operating in EXT and the frequency exeeds 99.9999 MHz, leading zeroes are not blanked. 100 MHz will display 00000.0 kHz. If power is applied without the 500 kHz input or if a failure should occur in the time base divider circuitry, the pulse at U9028 (1) will go away, causing Q9013 to turn off. When Q9013 turns off, Q9011, which supplies the ground to the display driver, will turn off preventing damage to the display.

DR7 REMOVAL (Refer to Pictorial Fig. 4-1)

1. Unplug (5) five connectors (Pl through P5) from the DR7 board. Position cables carefully so that they will be free of the DR7 Board when it is lifted out. Remove the retaining screw and lock washer (adjacent to U9006).

2. Unplug the coax and blue wire from the filter module. Slide the grommet off of the coax and wire.

3. Grasping the board along both sides, tilt the rear portion of the board upwards at an angle sufficient to fully disengage the connectors and slide the board toward the rear of the radio. As this is done, note that the LEDs should slide out of the aluminum bezel at the front panel. NOTE: Do not tilt the board excessively before the display LEDs are free of the locating aluminum bezel, or damage will result to either the displays or the DR7 board.

4. Using the card puller supplied with the radio, hook one end under the front edge of the large hole adjacent to U9008 (shown in figure 4-l). Grasp the tool and pull upwards firmly, but slowly, to disengage one 12 pin, one 9 pin and two 3 pin connectors. Once the connectors have been disengaged, remove the card puller.

5. Once the display and connectors are free, lift the DR7 board straight up, allowing the coax to slide out of the clearance hole provided for it.

6. Now either the DR7 or Jumper Board can be plugged in on extender cards and the coax plugged into the filter module to service the radio.

DR7 INSTALLATION

1. Position (5) five connectors (Pl through P5) and associated cables to be free of DR7 board during the installation. Check that all 27 connector pins on the DR7 board are straightened and perpendicular to the board.

2. Thread the Up-Converter coax through the hole (adjacent to C9015). Tilt the display LED portion of the DR7 board downward and slide the LEDs into the locating aluminum bezel at the front panel.

3. Start the 12 pin connector on the DR7 board (adjacent to U9006) into the receptacle on the Digital Control Board, noting visually that the connector pins are aligned properly with the receptacle

4. With the 12 pin connector sufficiently engaged, Start the 9 pin connector (adjacent to U9003) into the receptacle in the Translator board, again noting visually that the connector pins are aligned properly with the receptacle. Note that even though the alignment of the two 3 pin connectors cannot be visually inspected, their alignment will be proper if the pins were straightened and the 12 and 9 pin connectors are properly aligned.

5. Press down firmly, but carefully, on the DR7 board to fully seat all connectors.

6. Install the retaining screw and lock washer (adjacent to U9006). Plug in all (5) five connectors (P1 through P5). Slide the grommet over the coax and blue wire. Plug the coax and blue wire into the filter module, position the grommet in the chassis wall cutout.

(c) 1998-2012 D. PRODUCTS SA/NV - DRAKE is a registered trade mark of R.L. DRAVE COMPANY
No copy of text or image without a written authorization : email: JM CHERRY
Last updated on: 24 Dec 2011