Service manual

If, however, a conversion board can be fitted which uses the MC145106P IC then the

range of "N" codes is greatly extended and permits the standard crystal of either 11.1125 or

11.3258 MHz to be retained without the need to buy a specially made crystal. The

conversion board uses an Eprom to translate the switch codes into "N" codes for the new

PLL IC and the full range of frequencies from 28.105 to 29.695 MHz can be achieved,

together with 100 kHz repeater downshift on transmit. A complete conversion board is

available but the following information is given to allow you to design your own, should

you so wish.

For the 11.1125 MHz crystal the codes required for the "Novice" band start at HEX 101

for 28.105 MHz (ch. 1) and go up in steps of 1 to HEX 128 for 28.495 MHz (ch. 40). The

"N" codes for the rest of the

10 meter band rise from HEX 129 to HEX lA0 for 29.695

MHz. Notice that a transistor inverter is needed for the MSB.

For the 11.3258 MHz crystal the codes required for the "Novice" band start at HEX C1 for

28.105 MHz (ch. 1) and go up in steps of 1 to HEX E8 for 28.495 MHz (ch. 40). The "N"

codes for the rest of the

10 meter band rise from HEX E9 to HEX 160 for 29.695 MHz.

The six outputs from the channel switch produce HEX OF (ch. 1) to HEX 3B (ch. 40) and

provide the location codes for the Eprom inputs, together with connections "T", "X" and

"Y" on the PCB.

The circuit diagram shows the interconnections and, since they have been optimized for

simplicity of the PCB layout, the outputs from the Eprom are not connected to the inputs of

the MC145106P in straight order of numbers. The actual Eprom contents must, therefore,

have the individual BITs rearranged as explained on a previous page so that the PLL sees

the correct codes.

Note that link LK1 must NOT be fitted if an 11.3258 MHz crystal is used. Also, because

of basic differences between the MC145106P and the MB8719, which this conversion

replaces, it is necessary to remove the 1.5k

resistor which is soldered near to the MB8719

position in the CB radio.

The MB8719 is removed and the

16 pin ribbon connector soldered in its place but NOT in

the two holes used by MB8719 pins 9 and 10.

All the necessary information is given here, together with the complete Eprom codes, but

this is a most ADVANCED conversion so if you do not fully understand the way in which

the conversion works you should not attempt the conversion.