Page maintainer's note: The Icom IC706 family has been used as an HF and 2m remote base by several people.
My first exposure to HF remotes was a IC706 attached to a UHF repeater with a one HF frequency (14.258 MHz) and a few 2m frequencies.
I was pointed to a web page at the Wayback Machine that had the Bob Gass information below with a comment that it deserved to be at an active web site.
The N1EQ's website mentioned is also gone from the web but findable at the Wayback Machine.
Over the past 14 years I've learned a few things about the IC-706MKIIG that may help someone else.
- It won't turn on or powers up and then shuts down almost immediately or may turn off intermittently.
I understand this is one of the most common problems with this radio. Glue from a rubber spacer block under one of the boards reacts with a copper trace, causing it to corrode away and may damage the surrounding area of the circuit board. The repair is documented at N1EQ's website
N1EQ's website under "TECH" and "ICOM IC-706MKIIG Tech Notes". Mine started doing this and was down for about a year before I ran across the information to fix it.
- Intermittent Power Output.
My radio developed this symptom recently. I was afraid I might have a final going out but it turned out the fix was much simpler. While doing some testing to see what bands were affected the most I needed to move the power cable out of the way and grabbed the fuse holders. They were HOT. Further inspection showed the heating was in the area of the crimps, not the fuses themselves. The crimps were tight and looked ok. I heated them up with my 150 watt solder gun and flowed solder into the crimps. I put new fuses in (I've seen the small glass fuses develop problems as they get older) and the problem was resolved. Another area to look at are the pins in the power plug. They might need to be cleaned and bent slightly to make better connection.
- Preventive Maintenance Tip To Protect Your HF Finals
At 2014 ARRL Field Day one of the fellows asked me if I knew about the problem with the HF/6 meter connector shorting to the frame and blowing the finals in the 706. He related a horror story about a 706 he had owned that experienced that problem. The center pin of the connector gets pushed in over time and shorts out against the frame. I had noticed a few weeks earlier that mine was pushed in farther than the VHF/UHF connector but had not investigated it. My friend said the fix was to push the pin back out and put some kind of insulating spacer behind it. The next morning I had some down time (dead band) so I raised the hood and looked underneath. The center pin of my radio was within a 1/16 of an inch of shorting out. I cut a piece of Teflon from an antenna insulator and placed it behind the center pin after prying it outward with a screw driver. If you attempt this repair, the board above the HF/6 meter connector has to have the screws removed and then can be lifted up slightly and moved to the side. The UHF/VHF connector has a direct solder connection of the center pin to the PA circuit board and does not require this mod. Thank you Mark for the timely information that saved my finals!
- Sound Card Interface Problems and the KF5INZ "EASY DIGI" circuit PC board KIT.
I purchased this "cheap" interface kit from Ebay and assembled it. Very simple circuit with (2) 600 ohm transformers to decouple the RX and TX audio from the computer and an optocoupler IC to isolate the PTT from the serial port keying line. There are plenty of those circuits you can build yourself all over the internet. Usually the optocoupler most used is a 4N25. After assembly my interface would not key the PTT line on the 706. Grounding the PTT line would make it transmit. I sent an email to the vender of the kit and his response was to untie the VHF keying line from the HF keying line (most diagrams show pin 3 and 7 connected together on the 13 pin plug and I had done this) as their product was not able to key both of them. I did as instructed. It still would not pull the PTT low enough to key the radio. After a bit of reading I found a blurb about someone mentioning some models of Icom radios required a lower impedance to key them and I theorized the fix was to increase the LED drive current in the optocoupler to turn on the photo transistor "harder". After studying the data sheet on the 4N25 and figuring out the internal resistance of the device, I did some number crunching (Ohm's Law) and came up with 8 ma of LED current in the present circuit. My circuit had a 430 ohm resister as the current limiter so as a quick fix I paralleled a 470 ohm resister from the parts bin as that was the closest value I had. The resistance of the current limiter was now 224.5 ohms (originally 430 ohms). The internal resistance of the LED is 150 ohms for a total of 374.5 ohms. More number crunching estimated about 13.3 ma of LED current now and the PTT was pulled low enough so the TX keyed. The 4N25 data sheet says the maximum LED current is 60 ma so this increase in LED current is slightly less than 25% of maximum. The only other concern is pulling too much current from the RS232 port. A little more research turned up information that a mouse pulls about 10 ma. So if each pin on the RS232 port can supply at least 10 MA, using both the DTR and RTS lines isolated through diodes as most of the interface circuits have to isolate the lines from each other should prevent any over current problems as the total current draw should be split between them.
- USB to Serial Cable Generates RFI.
The cheap chinese usb to serial cables I have all experienced this same issue. Adding ferrites to the cable made no difference. Closer inspection revealed the reason why. The shielding (what little braid there is around the foil) is not connected to the shield of the USB connector or the DB9. Scraping back some of the plastic covering and soldering a small wire to the USB shell and then scraping away some insulation and soldering the wire to the braid took care of this problem. RFI was cured!
Contact Information:
The author, Bob Gass N4FV can be contacted at: his-callsign // at // yahoo // dot // com.
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This page originally posted on 27-Dec-2024.
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