Mounting/Testing Board 2

Mounting/Testing Board 1 || Final Connections || Adjustments || Tuning the Receiver


Mounting Board 2
Testing Board 2
Second Mixer || Crystal Oscillator || Crystal Oscillator Amplifier || 455 IF Strip
BFO Amplifier || Audio Pre-Amp/Audio Amplifier

Making Connections

See Making Loops for Connections on the Boards for making easy connections to the board for testing and completing the board. Three sets of loops are needed: Xtal Filter IN/Ground, 12 VOLTS/GROUND, and SPEAKER/Ground.

Use long enough cable lengths so that the top board can be easily lifted to one side in case some diagnosis or corrections are needed on Board 1.

____Connect +12 Volts to the +12 Volt and Ground connections near the AGC Detector at the edge of the PCB. Picture
____Be careful with polarity reversal. Use diode protection if a mistake might be made in connecting the board to 12 Volts.
____Use a 1-2 amp diode at the 12 volt main connection to prevent accidentally hooking up the receiver with reverse polarity. (This diode is not currently supplied with the kit.) The band end of the diode is connected to the 12 Volt connection and the anode end connected to the power supply.
____If you are using a 13.8 Volt power supply, put 3 diodes in series to drop the voltage to approximately 11.6 volts for the receiver. Cathodes (band side) go toward the receiver B+ and the anodes go toward the 13.8 Volt supply. The receiver likes 12 volts or a little below for best operation.

Another type of connection is to use RCA phono connectors. I found that a lot of them can be soldered to the board.

Mounting Board 2

____A space of approximately 1-1/4" is needed between the boards (one short 1-1/4" spacer). Closer spacing may need a shield to keep adequate isolation between the boards. Note with this spacing, turning the knob on the DDS VFO may interfere with the knob on the BFO.

A knob for the DDS VFO that has a dimple in the face so it can be turned in the front might work with the shorter spacer between the boards.

The spacing below is 1-7/8" with the longer female/female spacer and is plenty of room for the knobs on the BFO and DDS VFO.

____Mount Board 2 over the female ends of the spacers coming up from Board 1.
____Use 6-32 screws to secure the board on the spacers.
Feet screwed into the bottom spacers.

Testing Board 2


Second Mixer || Crystal Oscillator || Crystal Oscillator Amplifier || 455 IF Strip
BFO Amplifier || Audio Pre-Amp/Audio Amplifier


Second Mixer

____Second Mixer: Both LEDs should be on.

The Yellow arrow in the picture below shows that the LED brightness is controlled by the output of the Crystal Oscillator.

If the LEDs in the Second Mixer are not on, and the LED in the MOSFET Amplifier is on, the problem is in the Crystal Oscillator. Check for ~12 volts at the Drain (D) of the 2N5486 and that the 40/20 Crystal LED is on. Also check for a missed solder joint underneath the board.

If you feed the Second Mixer with a DDS or other Signal Generator, the LEDs will indicate the drive level so it can be adjusted to the correct level - any light in the LED will make the mixer work, higher drive levels will increase amplification.

Documentation will be added later showing how to drive the Second Mixer, with the MOSFET Amplifier, with a digital signal generator (DDS or Si5351A) to drive the Second Mixer to allow any Crystal Filter frequency to be used to generate the 455 kHz output.

This is a good time to double check the soldering at the T4-6T transformers. Use a magnifying glass or take a picture with a camera at high resolution and take a second look to make sure they are good.

Troubleshooting


Crystal Oscillator

With the BLT, the same crystal, 3.547 MHz, is used in both filters. The 4.000 MHz crystal is the only one used and the crystal switching is locked onto turning on the 4.000 MHz crystal.

The LEDs in the Second Mixer indicate drive from the Crystal Oscillator. Medium bright LEDs indicate that the oscillator and Mosfet Amplifier are working.

Troubleshooting


Crystal Oscillator MOSFET Amplifier

____Crystal Oscillator Amplifier: The LED should be on.

Troubleshooting


455 IF Strip

____455 KHz IF Strip: All three LEDs on the IF strip should be on. At one of the AGC connections, use a wire with clip leads and connect the AGC to Ground.
____The first two LEDs in the strip will turn off, the third one will remain on. Note: With the SWL build, all three LEDs will go out.
____Remove the wire after testing.

For SWL Builders:
The following modification will enhance AGC action if you are having problems with very strong AM Broadcast signals. Also works with the Ham Band version when dealing with local strong SSB or CW signals. If you are having a little distortion on strong signals, apply AGC to the Crystal Oscillator Amplifier as shown below.


Picture and modification by Dan McCabe, WA8YYE

Troubleshooting


BFO Amplifier

____455 KHz BFO Amplifier: The LED should be on. Turn the "Gain Adjust" pot clockwise at the amplifier and the LED should turn off.
____Turn the "Gain Adjust" counter clockwise so the LED is turned back on.

Troubleshooting


Audio Pre-Amp/Audio Amplifier

____Audio Pre-Amp/Audio Amplifier: Connect a speaker to the speaker terminals at the right of the 9779 audio amplifier, near the edge of the PCB.

____Touch a finger to the input of the Audio Pre-Amp, at the 1.5K resistor, next to the 10mfd capacitor. Hum from the 60 cycle house wiring should come out of the speaker.

____Touching the center connector of one of the 10mfd tantalums at the Bold "Audio Control" box will bypass the Audio Pre-Amp, and will also give a 60 cycle hum out of the speaker. If the 60 cycle hum test did not work at the 1.5K resistor, this test will isolate the problem circuit.

Troubleshooting

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Last Update: 8/5/2020
Web Author: David White, WN5Y Free Website Translator