External ALC mod for the IC-765 - A DC-to-DC charging challenge

[wb2hjk]

I’ll appreciate all your inputs - thanks in advance!

I successfully built the external ALC mod and have been using it a while now. However I’m taunted by the ever continuing replenishment of 9v batteries. I was challenged. I built circuit based using a Buck converter, hoping it could directly feed DC into the external mod, using the DC from the DC jack on the back of the 765. But I could not get it to work.  It seems it cannot because it “still sees” the circuitry of the 765.  Is there a way to isolate this “path”, perhaps with diodes?

[K8DI]

If I understand this mod and ALC, the ALC is a negative voltage, not just a reduced voltage. You’d need a converter that provides negative 9 or 12 volts to then connect the pot to and on to the ALC.  is the buck converter you have just a step down or does it provide inverted/negative output?  I found this on Amazon which may do the trick if you’re just using a step down..
https://www.amazon.com/Positive-Regulator-Converter-Boost-Buck-output±12VDC/dp/B07TT1KSMM/ref=sr_1_10?crid=LZ5TG9PFBI6W&keywords=Dc%2Bdc%2Bnegative%2Bconverter&qid=1699270109&s=electronics&sprefix=dc%2Bdc%2Bnegative%2Bconverter%2Celectronics%2C81&sr=1-10&th=1

Ed

[W1GFH]

I use this inexpensive adjustable regulated DC supply. Makes adjusting the ALC bias voltage simple and dependable.

https://www.amazon.com/ALAMSCN-Adjustable-Regulator-1-25V-12V-Electronic/dp/B09XWWVY96/ref=asc_df_B09XWWVY96/?tag=hyprod-20&linkCode=df0&hvadid=642112814556&hvpos=&hvnetw=g&hvrand=1881671859552129751&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9001863&hvtargid=pla-1944626922200&psc=1

[ki4nr]

I don’t know what your technical capabilities are or if you even want to get into the radio. But your 765 has a 5 volt negative power source in the radio that runs many of the rigs op amps. It’s a converter on the display board. If you look at the schematic (download the service manual) of the main board , Plug J-12 has the (pin2) negative 5 volts on it. If you follow the board traces jumper W202 or W176 can be tapped with a wire from the top of the board for the -5 volts.

Lucky for you Icom has a spare unused RCA jack on the rear of the radio. You can run the wire from one of the jumpers on the main board to that rear RCA and you have -5v power for the external ALC negative pot circuit. One thing and this is super important be sure to put a current limiting resistor in the wire to protect the radio and the negative convertor from damage in case you short out the RCA plug or some other craziness happens. Since that external ALC pot circuit pulls less than 1 milliamp a resistor from 4.7k to 10k should work. Also put a .0047 bypass capacitor at the rear RCA jack to keep RF out.

I did this mod on my 756pro, it also has a negative 12v power source. It was more complex because I had to pull the main board and cut a trace to use one of the pins on the accessory plug. But I had to remove the board anyways for other mods I did. Of course, I assume no responsibility for this mod or if you blow up your rig if you try it. I’m just putting it out there for reference and general info.