The objective is to install a DFD2 display in a Heathkit SB-303 where the zero set scale assembly is located.
I
purchased a DFD2-301 kit with the back light option.
Paid via Paypal; the kit arrived very quickly. The assembly was fairly straightforward. Could have used a magnifier during the soldering
assembly. The assembly is for people with a
steady hand and good eyesight. Otherwise get
the already assembled option. The only
problem I had was after assembly and initially tested, there was no display. I found that the contrast pot needed to be turned
fully CCW and then all was OK.
I
connected the backlight as suggested in the instructions, using a jumper from pin 1 to pin
16 and soldering a 33 ohm, 1/8 watt resistor from pins 2 to 15. This powers it from the 78L05 regulator.
I
removed the zero set scale assembly and nylon follower from the SB-303; I did not remove
the front panel. I found that there was not
enough room to install the display in the vacant space.
I removed the LMO and extended the mounting slots another 3mm to the rear. When moving the LMO to the rear I found an
interference with a 6-32 screw in the rear. I
replaced the screw with a 4-40 and did a little filing on the corner of the LMO. The proper way would to move the screw about 3mm
to the right (LFF-looking from front). Of
course, the main dial needs to be loosened and moved to the front by the amount the LMO
was moved to the rear.
I
was then able to mount the display on the plastic dial window. This was accomplished by rotating the windows 180
degrees so that the white numbers are now on top. I
drilled two 7/64” holes very close to the top to accommodate two 4-40. These line up with two of the holes in the top of
the display (these holes were a little small, so they also got the 7/64 drill). 5/16” spacers were inserted between the dial
window and the display. The window was then
mounted to the dial pointer mounting bracket via the two holes already in the plastic
window. In the end, I had to put some spacer
washers between the plastic window and the mounting bracket.
It
was a tight fit but I was able to mount the display.
I installed insulating material on the LMO where the display might hit it. I removed the speed nut that is on the left side
of the LMO (LFF) because it hit the logic board. I
ran LMO, BFO and HFO cables to the rear panel and plugged them in using RCA plugs. Connecting to the SB-303 +10vdc provided DC power. Some of the metal from the display does show. This can either be painted or left as is; I
covered it with black electrical tape.
The
display gives the proper frequency readout and indicates USB/LSB/CW/AM. I found it necessary to install the level control
circuitry as described by AADE.
I
believe that the installation can be done without moving the LMO to the rear by only
mounting the display and remotely mounting the logic board.
The inter connection can be made via ribbon cable. This may also allow the display to be mounted in
the SB-401/301/101.
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KA0RRX
7/3/05