icom 706MK2G major failure
Posted: Fri Nov 25, 2005 10:46 am
snip from eham
recently have run into two other hams who now have had the same failure with their ICOM 706s' ... both have be scraped due to the bad service that ICOM has been promoting on this issue...
It appear that the Caps C188 and C604 both are rated for 16 volts at 1000uf... these are electric caps and as such have liquid in them which is corrosive... and currently the way that ICOM instructs you to wire the radio up for mobile operation can lead to the failure of one or more of these caps... which can do irreparable damage to your 706 if they burst or catch fire by shorting out in the process of their explosion...
Here is why....
The instruction manual says to hook the leads of the 706 directly to the battery... make a good connection... as it says that can handle at least 30 amps... fine..
However, when you check the shop manual circuit diagram... it shows that the power is ever present on the input to the radio.. and also the PA amp section that these little caps are associated with.
Why did they do this.... well ICOM being cheap didn't want to switch the high current PA section on and off... by putting some device in that would handle 30 amps... so what they did was wire it so that the finals are hot all the time as a direct connection (see drawing) and its associated circuitry of which these two caps are in line with.
So what's the beef...
Well if you go starting the car... your starter can develop spikes that amount to several times the input voltage... thus the little caps which are rated at 16 volts are right at what the battery voltage and charging system is... So when you go to start the car you could be placing at least 2 to 3 time (30-45 volts) of the battery voltage across them.. thus, we have exceeded the voltage rating of the caps... some one at ICOM didn't quite figure that out right... I would think...
What is also amazing on this radio is that someone has not had one of the PA transistor fail and cause a fire or at the least flatten the battery while it is un-attended... if they failed also... something not to be taken lightly...
When we called ICOM... not once but 4 times now to present this design flaw to them and to see if they will back the defective material or part... due to their under sight.. we were told that for 90 bux an hour they would fix it... (1 hr MIN) plus the shipping to and from can become a expensive issue...
So what's the fix...
Well about the only thing that you can do is to put either a relay or a ckt breaker in series with the power leads going to the 706... Sure its going to be costly.. but, how much is your car worth... or the radio... as it appears that ICOM is reluctant to fix the bad capacitors when they fail... which then could lead to the radio becoming a boat anchor eventually...
I know K0BG is going to differ with me on this but, I prefer that a aviation toggle switch circuit breaker (such as what can be gotten from Chief Aircraft parts) be put in the positive feed line... Here you can have a selection of a toggle switch or a rocker switch similar to what aircraft call the avionics master switch... that does about the same as what you need to do in the car... and that is remove the power from the radio until after you start the car... and the charging system has settled down.
It is the only way that you will be able to isolate the 706 from the rest of the electrical system... as their on/off button on the front does not remove or apply power to the PA board as shown.
I am against using a dual relay contactor as the points of the relay will eventually develop some IR drop and again your going to suffer the effects of a low voltage application... and cleaning the contact is some what of a chore. While the good quality 30+ circuit breaker that has the regular toggle switch on it was made for the aircraft environment and thus can stand the test of time without having problems...
Conclusion
If you own a ICOM 706 and don't make the modifications to the power input leads... you can stand a chance of damaging the radio due to their deficiencies and/or loss of electrical to the car leaving you stranded or thinking that the battery is no good... worst yet... come back and find it had a color change as it burnt up... if the 30 amp fuses don't work as advertised...
I am sure a lot of people who own a ICOM 706 are not aware of the design deficiency and the fact that if it happens your going to have to pay for it.... thus we call it to your attention... as I am sure ICOM would never...
recently have run into two other hams who now have had the same failure with their ICOM 706s' ... both have be scraped due to the bad service that ICOM has been promoting on this issue...
It appear that the Caps C188 and C604 both are rated for 16 volts at 1000uf... these are electric caps and as such have liquid in them which is corrosive... and currently the way that ICOM instructs you to wire the radio up for mobile operation can lead to the failure of one or more of these caps... which can do irreparable damage to your 706 if they burst or catch fire by shorting out in the process of their explosion...
Here is why....
The instruction manual says to hook the leads of the 706 directly to the battery... make a good connection... as it says that can handle at least 30 amps... fine..
However, when you check the shop manual circuit diagram... it shows that the power is ever present on the input to the radio.. and also the PA amp section that these little caps are associated with.
Why did they do this.... well ICOM being cheap didn't want to switch the high current PA section on and off... by putting some device in that would handle 30 amps... so what they did was wire it so that the finals are hot all the time as a direct connection (see drawing) and its associated circuitry of which these two caps are in line with.
So what's the beef...
Well if you go starting the car... your starter can develop spikes that amount to several times the input voltage... thus the little caps which are rated at 16 volts are right at what the battery voltage and charging system is... So when you go to start the car you could be placing at least 2 to 3 time (30-45 volts) of the battery voltage across them.. thus, we have exceeded the voltage rating of the caps... some one at ICOM didn't quite figure that out right... I would think...
What is also amazing on this radio is that someone has not had one of the PA transistor fail and cause a fire or at the least flatten the battery while it is un-attended... if they failed also... something not to be taken lightly...
When we called ICOM... not once but 4 times now to present this design flaw to them and to see if they will back the defective material or part... due to their under sight.. we were told that for 90 bux an hour they would fix it... (1 hr MIN) plus the shipping to and from can become a expensive issue...
So what's the fix...
Well about the only thing that you can do is to put either a relay or a ckt breaker in series with the power leads going to the 706... Sure its going to be costly.. but, how much is your car worth... or the radio... as it appears that ICOM is reluctant to fix the bad capacitors when they fail... which then could lead to the radio becoming a boat anchor eventually...
I know K0BG is going to differ with me on this but, I prefer that a aviation toggle switch circuit breaker (such as what can be gotten from Chief Aircraft parts) be put in the positive feed line... Here you can have a selection of a toggle switch or a rocker switch similar to what aircraft call the avionics master switch... that does about the same as what you need to do in the car... and that is remove the power from the radio until after you start the car... and the charging system has settled down.
It is the only way that you will be able to isolate the 706 from the rest of the electrical system... as their on/off button on the front does not remove or apply power to the PA board as shown.
I am against using a dual relay contactor as the points of the relay will eventually develop some IR drop and again your going to suffer the effects of a low voltage application... and cleaning the contact is some what of a chore. While the good quality 30+ circuit breaker that has the regular toggle switch on it was made for the aircraft environment and thus can stand the test of time without having problems...
Conclusion
If you own a ICOM 706 and don't make the modifications to the power input leads... you can stand a chance of damaging the radio due to their deficiencies and/or loss of electrical to the car leaving you stranded or thinking that the battery is no good... worst yet... come back and find it had a color change as it burnt up... if the 30 amp fuses don't work as advertised...
I am sure a lot of people who own a ICOM 706 are not aware of the design deficiency and the fact that if it happens your going to have to pay for it.... thus we call it to your attention... as I am sure ICOM would never...