Yaesu FT-847 volume control mod
I often use the FT847 at low volume,squelch open, to be able to pick any propagation opening,and it is impossible to set it it at a comfortable audio level.
The modifications that i have found on this subject searching the net ,(basically inserting a resistor in serie with pin 1 of the AF amplifier),improved it a bit,but not enough.They lowered the main volume,and did really not fix the "jumps" problems.
So , i decided to look at the schematic, and found a very simple solution, that is working really fine.
The volume control is now truly analog,and goes smoothly from 0 to full,almost as loud as before.
In the ´847,the volume control potenciometer is directly connected to the front panel microprocessor,wich aparently makes the A/D convertion.
My idea was to disconect the potenciometer, wire the circuit in full volume position, then use the (now unusued) potenciometer to conventionally control the volume, directly at the input of the AF amplifier.
First, the usual precautions and disclaimer about modifying your radio.don´t forget to disconnect everything, and use antistatic precautions.
Now,remove both covers, and flip down the front panel so you can have access to the back of the volume potenciometer:
As you can see on the picture, you will have to:
Remove the solder from the first pin (from right) of the volume control potenciometer.It is the closest to the radio,oposite of yourself (if you are facing the radio, as you surely do :-) )-
Scrap with a sharp knife (or something else) around the pin to be sure there is no more contact.(It is easy).This pin will be left alone unconnected.
Bridge the small black resistor.I have removed it and made an (ugly) solder bridge, but you can solder a small wire.It will look better, and can be removed if you decide to.
Cut the trace between the center pin of the potenciometer and the circuit so it becomes isolated.
The last pin remains to ground.
Here is how it should look:
Now all you have to do is to solder a thin wire from the center pin of the potenciometer to the back of your radio, at the input of the AF amplifier IC:
You can close the front panel now,turn over your radio and find the audio amplifier.It is located at the rear right of the 847(when you face the front panel,as always).
The wire can be joined to the other ones and fits nicely.
You have to solder this wire between the SMD capacitor and the resistor that are in serie with the pin 1 of the IC.There is no much room for the iron, but it can be done quite safely.there is nothing to diconnect here.Just solder the wire and enjoy your new radio!
You can connect the power supply now and check if everything is OK.
This picture is not too good , but you can´t miss the place once you are looking into the radio.