Radio Shack model TRC-485
Note:there is some erroneous info on the 'net concerning this mod.
THIS ONE IS CORRECT!
For technical help with this mod,email lb-admin@techemail.com.
Note:this procedure is for educational purposes or for 10 meter use for licenced operators only.
Transmitting on unauthorized frequencies is illegal and the radio operator's responsibility.
You will need the following tools:
1.a good iron with a fine tip
2.desoldering equipment
3.a magnifying glass(I use a bench mounted,lighted type)
4.a dental pick
5.screw driver
6.a steady hand!
The easiest way to work with the PLL is to completely remove the front
panel assembly from the radio.The front has to be taken apart and the
board desoldered from the main board.Once its free,you can work with it
much easier.
On one corner of the chip is a round mark,that designates
pin 1.The pin count is counter clockwise.Using the dental pick to lift
the pins,unsolder pins 31,32,33 and then connect pin 34 to where they
were soldered.
To change bands:
Remove board from panel:
1. Locate the track ,on the front of the board,that comes from the NB switch (SW207) and connects
to pin 28 of the CPU, and cut it quite close to the switch (as shown below), (pin 28 is shared with the CH9 button,so disconnecting the entire track or cutting it after the CH9
switch WILL cause other problems !)
2. After cutting the correct track run a jumper wire from the switch
(on the PLL side of the board) to one side of the MODE button (SW204)(as pictured below),
this MUST be the side that goes to pin 29 of the CPU (the same side
that also connects to the SCAN switch), OR if you are not sure
you can run a jumper wire directly to pin 29 of the CPU.
Reassemble the front panel to the main board and,if everything was done correctly,you will now have:
'NB' button changes the radio to the following bands:
A:25.165-25.605
B:25.615-26.055
C:26.065-26.505
D:26.515-26.955
26.965-27.405(Class D Citizen Band)
F:27.415-27.855
G:27.865-28.305
H:28.315-28.755
I:28.765-29.205
J:29.215-29.655
As a note of interest,when the radio is turned on it will have four
modes...blank,AM,USB and LSB.Initially it comes on in the blank state
where there is no TX or RX.Pressing the mode switch will give you the
active modes.
The NB button changes the bands,all are lettered in the
display except for the CB band.Full coverage of all bands is not
possible.Adjusting the VCO coil (T8) will give specific bands coverage.If you tune it for 25
Mhz ops you will lose the top bands and vice versa.I recommend adjusting it to cover your operating needs.
RV10:AM power adjust,RV6:ALC adjust.
Recieve section will need realigning for 10 meter operation.
********
Front panel removed,showing the PLL.Pin 1 is on the bottom left .
Pins 31,32 and 33 lifted and pin 34 connected.
Where to cut trace to SW207.
Install jumper.
Resolder front to main board.
BAND A,ch 1
Band J,ch 40
VCO coil location.
