Any common problems with the Ic 718?

[W5WSS]

N4pse I think you are on the right track here. The problem may be a poor solder joint on the pa board but the underlying question that concerns me is whether or not Icom has suffered a bad batch of electronic parts. I wonder if our rigs were constructed around the same period?

[W5WSS]

While attached to the 50 ohm non inductive dummy load today I observed two different problems #1 this output power drop-off from 100 watts to 2 watts  occurs on 17M 15M 12M 10M only. #2 The rig just transmits full power regardless of mode this includes ssb where I am NOT modulating. During the #2 problem  I noticed that when I change mode via the mode select push button It has no effect on the transmitted signal but rather it just transmits full out of control output while simultaneously displaying normal swr reflection normal alc just full power output when pressing the ptt switch regardless of mode. None of the two problems has ever been manifest on 20M and down. So this odd problem is with the 17m 15m 12m 10m bands.

[W5WSS]

Any more problems? please feel free to add yours.

[W5WSS]

I discussed the symptoms in great length with Kk5j here in town and he directed me to the wiring harness that is located near the j17 trimmer. I carefully unplugged it and properly cleaned it plugged it back in. The transmitter is now working properly on 17m 15m 12m 10m. The harness does have some tension on it as a function of routing, whether this is a problem time will tell. I must say This has been a real thorn for awhile as I went looking for common mode issues. On a positive note I have a very healthy antenna system and power supply system in the mobile. Please feel free to post any other issues with the 718 thanks.

[WA8MEA]

I've had numerous 718's over the years.

One common denominator: They all went nuts (as you describe) with excess RF in the shack.

Also, I've had other rigs perform as you describe that don't have large enough wiring to carry the current from the PS to the rig....even in short lengths.

I've also had Yeasu's go nuts with RF when connected to ANY power supply, but work perfectly fine with a marine battery.

So...have fun!  Experimenting can be educational!

73, Bill

[W5WSS]

Thanks Bill. Yes while it is certainly possible that a low voltage condition would or could depending on a few variables. I have several contingencies with respect to power supply and voltage drop has been investigated  and dismissed as well as the various antenna systems found to be without fault. the latest theory is that the problem is in fact within the rig but I am only speculating at this time and will reveal more upon discovery meanwhile fellas keep posting your issues ans comments with otherwise great little rig. Thanks and 73

[W5WSS]

N4pse yes I am looking at the various pitfalls associated with transmitter fold back  protection circuitry. Interestingly within the many specs contained in the Mitsubishi data sheet of the 2SC2904 a maximum temperature of 150 degrees in every case causes total shut down of the mosfets output power. As you know there is a thermal resistor that works with two separate transistors to control the hi and low fan speed for temp control of the finals. Heating and cooling with time about 30 seconds in my case for total restoration back to 100 watts pep. Due to the possibility of damage caused by a problem with cooling I must stop transmitting until that possibility is ruled out.

[AD6KA]

#2 The rig just transmits full power regardless of mode this includes ssb where I am NOT modulating.

How can the rig transmit ANY power in SSB when you are NOT "modulating"?

If the rig truly is in SSB mode and you are keying the mic
*without* speaking into it, or injecting an audio signal into
the mic circuit (PSK, AFSK, etc), then there should be no power output at all.

Mitsubishi data sheet of the 2SC2904 a maximum temperature of 150 degrees in every case causes total shut down of the mosfets output power.

Are you looking at the "Collector Dissipation vs. Ambient Temperature" chart?
Collector dissipation is not the same as "output power".
And that's 150 degrees Celsius....302 degrees Fahrenheit.

[W5WSS]

Ad6ka are you asking me? I said 150 degrees. I also said it outputs power even when I am not modulating the transmitter when in the ssb mode. I am discussing the symptoms. I asked you a question that you did not answer.

[KT4WO]

I must agree with AD6KA, I have the 718,,,had it for 5 years without ANY problems. This is a VERY
solid radio that is 100% duty cycle. You have other problems. Its a jumper..or something would be my bet.

You are going in directions that you don't need to and don't sound qualified to.

Go buy a new jumper, and stay away from the finals.

Trip - KT4WO

[KT4WO]

---AND--- reset the SWR protection!!.. or you will be replacing the finals.

You have RF problem or maybe a low power supply issue... Don't know for sure, but
it does not sound like a radio issue per se.

Try a new jumper, power supply and dummy load. THEN if you still have the problem...maybe its the
radio:) 

Trip - KT4WO

[KB4QAA]

IMHO, there is no reason for the average ham to be messing with the SWR protection settings on a 718!!  EVER.

If one doesn't have a well equipped lab, and one doesn't have either formal training or years of repair experience you are going to screw up radios, not fix them.

I feel like a lot of the 'supposing' here has been chasing self painted zebras rather than something being originally wrong with the radio.

I recommend doing a hard reset on the radio and taking it to an experience ham technician who has the service manual, rather than doing any more self repairs.

Good luck!

[W5WSS]

More than a month ago, prior to starting this thread I did the hard reset. The swr set procedure is in the service manual and is easy to do. Ad6ka comments are after the fact and only relevant with respect to a Properly working rig and is not the final word on this subject because contrary to his critiques (as opposed to helpful hints) one of the two symptoms with my 718 is that the rig is in fact outputting out of control even when in the ssb mode and not modulated by the user. Leaving me with only one problem remaining and that is this, after about one minute of transmitting at full power on ssb the rig drops to 10 watts pep and remains so unless I stop transmitting and I wait 1 minute which at that point will repeat exactly again with 100 watts down to 10 watts. I fixed the first problem leaving only the heat related thermistor issue. The spirit of this thread was meant by me to be helpful and informative associated with the common problems we experience with the Ic 718. To those whom wish to post their issues with this otherwise nice rig please feel free to do so It is not my intention to be critical of our fellow ham operators on whether or not they are qualified to read and use their service manuals. 73

[W5WSS]

Kt4wo hello did you know that Icom redesigned the pa board and use different finals than they did 5 years ago? I have already isolated and fixed one of the two transmitter problems. 73

[KT4WO]

"Kt4wo hello did you know that Icom redesigned the pa board and use different finals than they did 5 years ago? I have already isolated and fixed one of the two transmitter problems. 73 "

No---I did not.
But....When someone starts disabling the SWR protection, It make me question their
qualifications.

Good Luck and 73

KT4WO