TRC 490 AM/SSB 40CH BASE PLL LOCATION??? MB8719 PLL I'm told...
 

Need location plse. Has the PC-385AG PCB board. It's FS also. Listing
to follow next week with dig picture...

don't touch it if you dont have a clue where it is...

-- Realistic TRC-490 and other radios that use the PC-385 PCB.
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.


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How to increase the modulation level.



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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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On the internet, no one can hear you modulate.



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