Mods

This page describes some modifications for the Uniden / President Washington, Stalker IX and Realistic TRC-490 and other radios that use the PC-385 PCB.


How to add more channels


If pin 10 of the PLL is tied low, remove the ground and pull the pin high to go down 64 channels ! (as found in the Washington)

If the pin is tied high, remove the voltage and ground the pin to go up 64 channels !

The state of pin 10 depends on the country that you are in and how it has been modified for the frequencies that are used.

The loop crystal can also be changed to give you more bands of channels if needed, you can use my crystal switch to switch whatever crystals you use to give you the bands that you want.


How to increase the modulation level.


On the Washington and some other versions of the PC-385 board the AMC uses a fixed resistance to limit the amount of modulation that can be produced (typically to just 75% !).

TR32 is the AMC transitor, however, there are two really easy methods of increasing the modulation.

The first method involves replacing the fixed resistor with one of a lower value, the resistor is a 1.5 KOhm and is located directly next to TR33 (it is part number R105, which is not marked on the PCB), it connects between TR33's base (the left leg, one end goes to a diode marking) and earth, replace this resistor with a 500 Ohm.

The second method is better, but, not all models can use it, it depends if the large transformer (marked as T1) is installed towards the rear of the PCB (next to L10), if it is not installed (as is the case with the Washington) you will see a silk screen marking for a preset pot inside the outline for the transformer (some radios already have a VR installed in this location to adjust the AMC), this is what you need to do for this mod:

Remove the 1.5K resistor in the D70 location that is next to TR33.

Install a 1N4148 silicon switch diode in the D70 location.

Install a 1 KOhm preset pot into the vacant position at the rear of the board (next to L10 inside the marking for the transformer).

Connect a jumper wire between the vacant hole that connects to D70 and the vacant hole that connects to the preset pots wiper (it is towards the front edge of the pot).

You have finished, all that needs to be done is to set the AMC level with the new VR (see the alignment instrucions for this).


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