Hardware Hacking

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

The mod is to increase the amount of channels of the Albrecht SS485,Dragon TRC-485 or Radioshack TRC-485 that originally comes with 40 channels from 26.965 to 27.405.

The mod is to alter the pins of the 80 pin microprocessor (Albrecht SS485=SY202, Dragon TRC-485 = SY201, Radioshack TRC-485 = HYU4011Q06 FP), so that the pins where either disconnected from the circuit (open) or connected to the circuit (close), for pin 31 (open), pin 32 (open), pin 33 (open), pin 34 (close) the radio then had 400 channels of transmission/reception.

To control the bands you must touch pin 3 of the CPU with pin 29 for one second.

You can re-wire the NB switch to do this (the NB button is connected between pins 3 and 28), this is easy to do, read on !

Refer to the diagram below to assist with the description:

1. Locate the track that comes from the NB switch (SW403) and connects to pin 28 of the CPU, and cut it quite close to the switch (between SW403 and SW405), but not too close, as you need to solder a jumper onto it on the switch side of the cut, (pin 28 is shared with the CH9 button (SW405), 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 cut track (on the NB switch side of the cut) to one side of the MODE button (SW404), this MUST be the side that goes to pin 29 of the CPU (the same side that also connects to SW406, the SCAN button), OR if you are not sure you can run a jumper wire directly to pin 29 of the CPU.

3. That is it, your done !

Bands available after the modification:

25.165-25.605
25.615-26.055
26.065-26.505
26,515-26,955
26,965-27,405
27,415-27,855
27,865-28,305
28,315-28,755
28,765-29,205
29,215-29,655

To transmit / receive on all of the 400 channels it is necessary to adjust the VCO.