Service manual

Switch Cod

Before you begin a conversion you should ALWAYS use a voltmeter to determine the

switch codes for every channel. Don't rely upon a book to tell you because you'll be

awfully confused if the book is wrong or refers to a different model. Always check. If you

start to design a lot of conversions it will help if you make up a row of

LEDs with

transistors on

stripboard, which you can connect to the PLL input pins. Flicking the

channel switch round causes different

LEDs to light as the code changes and it is an easy

matter to write them down. Keep records of everything you do because it's surprising how

much is forgotten after a couple of months. The switch codes feeding the

Eprom inputs

specify the locations of the output codes. DO remember, however, that the complete

location or "address" comprises the codes from the switch AND any voltage on the

remaining

Eprom inputs. These inputs can be used to switch from one bank of codes to

another in order to change band. Unused inputs should be connected to 0 volts because, if

left floating, they will pick up any stray RF which could be interpreted as a "1". I learnt this

the hard way when

a radio under test actually changed band on transmit. Great for duplex

operation! You can create this effect deliberately

if you need TX downshift for Repeater

operation. Use the rig's own TX line to switch one of the

Eprom inputs thereby swapping

the code bank to one whose codes are programmed for 10 channels lower.