Ramsey Electronics CB1 User Manual - page 11
CB-1
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The circuitry you're working on now is the display driving circuit. When the
input to the circuit is low (near ground or zero volts), Q6 is off, which turns Q4
on, turning on only the address display. When the input is high (near +5V),
Q5 turns on and only the mode display is on. When the circuit is operating,
this switching is fast enough that it can't be seen by the eye (about 100 to
1000 times a second). This technique is called Multiplexing and is used with
virtually all displays, from calculators to TV sets!
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39. Install R22, 10K ohm resistor (brown-black-orange).
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40. Install jumper JMP10.
Whew! You're halfway done with the main board. Take a break to give your
eyes a rest. When you come back, check all of your solder connections,
looking for bridges or cold solder joints. Don't be afraid to reheat any of the
solder joints that you find suspicious; all parts in this kit would be almost
impossible to damage with extra heating. The only thing you have to watch
for when soldering are the PC board traces overheating and lifting off of the
circuit board.
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41. Install Q1, 2N3904 transistor. Watch the positioning of the flat side.
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42. Install Q2, 2N3904 transistor, watching the positioning of the flat side.
Transistors Q1 and Q2 are used to key an external radio.
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43. Install C20, .01uF disc capacitor (marked .01 or 103 or 10nF). This is
a bypass capacitor which prevents noise from the operation of the
microprocessor from finding its way back into the power source.
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44. Install jumper JMP8.
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45. Install C13, .01uF ceramic capacitor (marked .01 or 103 or 10nF).
This part acts as a DC blocking capacitor to the mike input of the ISD
chip (same as the function of C19 earlier). This blocks the DC from the
key detecting circuit and mike line.
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46. Install R23, 10K ohm resistor (brown-black-orange). This part,
combined with Q8, Q9, R22, R20, and R17, pulls the start line low when
there is a resistive load placed across the mike input, this has the same
effect as pressing the start switch. PA2 of the processor detects this and
activates accordingly.
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47. Install jumper JMP3.
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48. Install Q8, 221334 PNP type transistor. Notice that this transistor
does not have a fully rounded side like the others, but a semi-rounded
side and a fully flat side. You can most easily identify the flat side by
noting that the round side does have a curve to it on the side edges.