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Author Topic: Any common problems with the Ic 718?  (Read 15233 times)
W5WSS
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Posts: 1657




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« on: December 13, 2010, 12:15:36 PM »

I have been using an Icom 718 for a few years and has been a good rig until recently. I am wondering if anyone else has experienced any problems with their transmitter. Mine has very recently started shutting down.and does so intermittently. The symptoms suggest RF common mode but until I can bypass everything in the system and look at it isolated with a dummy load I am guessing. Anyway I find it useful to ask if anyone has had their transmit shut down while watching the internal meter,mine will read some 75% deflection but in actuality is not transmitting. This question is mostly academic but could reveal some common problems we are experiencing. Thanks 73
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2E0OZI
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« Reply #1 on: December 13, 2010, 01:48:56 PM »

Just bought mine yesterday still with 8 months warranty left on the clock, but any replies will be of interest to me!
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KE4ILG
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Posts: 149




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« Reply #2 on: December 13, 2010, 02:08:49 PM »

This may be an overly simplistic thing to check but I understand Icom's are finicky about the power supply.  If the voltage drops, which would happen when transmitting, it might cause what I understand you to be describing.  If possible trade out your power supply or hook it up to your vehicle and see if that solves you problem.  I had what seems to be similar problem with my Yaesu FT-950.  The fan to my switching power supply had stopped working and I had not noticed.  When I transmitted for a short time, shorter when on ssb instead of cw, the rig acted badly and shut down. The power supply was overheating and the output was not what it was supposed to be.  Replacing the power supply corrected the problem.  Out side of that I've heard nothing but good about the Ic-718.  73, Mike ke4ilg.
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K9WJL
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Posts: 183




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« Reply #3 on: December 13, 2010, 04:19:06 PM »

I wonder....
 I had a 706MK2G in the truck at one point, and the thing would shut down while tuning the screwdriver antenna on 40M.
Unplugging the external speaker while tuning eliminated the problem.
I don't know if this helps or not, but I wonder if the rigs share a similar design and I thought I'd throw it out there in case it was the issue.

73,
 Bill K9WJL
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AD6KA
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Posts: 2233




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« Reply #4 on: December 13, 2010, 04:40:21 PM »

I wonder....
 I had a 706MK2G in the truck at one point, and the thing would shut down while tuning the screwdriver antenna on 40M.
Unplugging the external speaker while tuning eliminated the problem.
I don't know if this helps or not, but I wonder if the rigs share a similar design and I thought I'd throw it out there in case it was the issue.
That sounds like a common mode current getting into the
radio issue, especially tuning a short loaded antenna on a band
like 40m. But through the external speaker input? Never heard
of that one.
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VA7CPC
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Posts: 2358




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« Reply #5 on: December 13, 2010, 04:57:11 PM »

My first thought:

. . . Check the power supply, DC wiring, _and fuses in the power cord_.

A loose or corroded fuse holder (or fuse) can masquerade as all kinds of trouble.   I just learned that the IC-7000 is notorious for "corroded fuse" troubles.

If it had a separable face-plate (a la IC-706), I'd suggest checking the wiring to that, as well.   But the IC-718 is a "one-box" rig.

                 Charles
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W5WSS
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« Reply #6 on: December 13, 2010, 05:46:27 PM »

A few minutes ago I connected the rig to a dummy load and it works normally. 100% every test. 100 watts output fine. I use this rig in my automobile on a hilltop stationary only. The only common denominator from that mobile antenna and to my other antenna system (rig is ungrounded in a second floor apartment) is that I do not have a grounding strap connected from the designated ground terminal on the rig to ground in either case. I have double checked both antenna systems for faults and find none. Perhaps a 6" long and 1" wide grounding strap connecting the rig's grounding terminal to the car frame could shed some more light on this new development it worked fine for a few years in the mobile. Not sure what changed yet. but am looking for the cure.
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W5WSS
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Posts: 1657




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« Reply #7 on: December 13, 2010, 08:03:57 PM »

Well...after some careful review of the service manual we see that there is an swr threshold setting that I changed from 1 to 2. the difference between a dummy load being purely resistive and an antenna that is above that threshold is the resulting difference. I think the swr cutback circuit was too sensitive at setting 1. You know it is interesting to note that nothing was mentioned about this in the manual that came with this brand new in box unit. There is much to be gained from the service manual too bad it was not included with the purchase of their new gear.
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W5WSS
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Posts: 1657




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« Reply #8 on: December 14, 2010, 06:29:48 PM »

Well here is an update. After reading through the suggested steps Icom wants us to connect the rig to a 100 ohm dummy load. eh em anyone have one of those? So in essence what we are doing is creating a window for the protective circuit to work within. I am able to set it to 50 ohms resistive but not the upper 100 ohm threshold. We are thinking the protective system which involves ALC ,output power, and current have grown apart for reasons not fully clear at this time but we need to complete a diagnostics for a more complete view of what is causing this erratic behavior and indeed rf common mode is always a possibility but may be only a minor player with this symptom.
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AD6KA
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Posts: 2233




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« Reply #9 on: December 14, 2010, 07:33:56 PM »

Quote
A few minutes ago I connected the rig to a dummy load and it works normally..
In the car with the battery, or at home with a power supply?  If it messes up in the truck, check the battery voltage at key down when it faults Both with and without a dummy load. Does it NOT fault if you turn the power down?
What kind of antenna are you using in the car and on what bands?
Quote
the difference between a dummy load being purely resistive and an antenna that is above that threshold is the resulting difference.
I’m not even going to guess what you are trying to say here.
Quote
I think the swr cutback circuit was too sensitive at setting 1..
Maybe, but you said the rig was “shutting down”.This usually means turning itself OFF.
Is the rig in fact turning itself off or is it a power foldback problem?
High SWR foldback does not turn the rig off.
The former sounds like a voltage problem, as has been mentioned, and the latter
sounds like an undetected antenna problem or coax short.
Regardless, you should set the SWR circuit back to the factory default
AND do a microprocessor reset before you proceed any further.
Quote
We are thinking the protective system which involves ALC ,output power, and current have grown apart for reasons not fully clear at this time but we need to complete a diagnostics for a more complete view of what is causing this erratic behavior and indeed rf common mode is always a possibility but may be only a minor player with this symptom.
Who is “we”? You have a qualified Tech helping you?
Not sure how circuits “grow apart”.
It’s impossible to even tell what is going on given little information on antenna type, bands used, modes, power levels tried,
power supplies, type of connections, etc…not to mention use of the rambling verbiage.
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WB6BYU
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Posts: 13045




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« Reply #10 on: December 14, 2010, 07:53:15 PM »

A simple way to make a 2 : 1 dummy load is to put two 50 ohm dummy loads in parallel using a T
connector.  If you need 100 ohms just add a quarter wavelength of 50 ohm coax between the T
and the rig.
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W5WSS
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Posts: 1657




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« Reply #11 on: December 15, 2010, 12:56:22 PM »

Ad6ka The rig is folding back in output down to less than 2 watts while simultaneously displaying a pegged high swr reading that is no fault of the various antenna systems that we have connected to it. The rig works perfectly normal 100% of the time when connected to a 50 ohm purely resistive and non inductive load. There is not a voltage drop problem as measured under maximum load and when measuring at the rig nor is there a lack of ample current available when pressed. We is plural for a friend of mine here in town. What we are going to try next is to adjust the swr set feature to rule out the possibility that something changed for reasons that are not clear yet. We are going to raise the set 2 feature by using a 100 ohm purely resistive and non inductive dummy load. We hope this will settle the issue. Do you know for a fact that the default procedure will include this? By the way your critique of how I structure a sentence was rude. If you want to Elmer than please be polite thank you.
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WB6BYU
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« Reply #12 on: December 15, 2010, 01:35:54 PM »

Did you use the same or different jumper cables for your various tests?  It sure sounds to me
like an intermittent connection in a coax cable, possibly the shield at some point.  It could
also be due to a cracked solder joint on the antenna jack, or an intermittent connection to
the center pin (such that some plugs make good contact and others don't, often due to
wear or corrosion on the plug or socket contact, or insufficient spring contact pressure,
often due to using a plug with too much solder on the end of the pin that spreads the
contacts apart.)

This is based on the behavior of the SWR meter in the rig:  if the SWR jumps up it shouldn't be
due to the shutdown circuitry.  (It might TRIGGER the shutdown circuitry, of course.)  If the
SWR is normal but a bit above the threshold, you should see it remain the same when the rig
shuts down.  (This presumes that the meter is programmed to respond in a "reasonable" manner,
of course, which isn't always the case with some microprocessor-controlled rigs.)

It is possible that some RF is getting into your reflected power sensor - again I'd look for a
broken bypass capacitor or poor shield connection if that is the case.  But I've been bitten
may times by poor connectors - perhaps the most common ones are BNC plugs where the
center pin has receeded into the housing, or worn down (especially from vibration when using
a rubber ducky on a bicycle.)  Some combinations of connectors make contact, others don't,
and it can be quite confusing.
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W5WSS
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Posts: 1657




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« Reply #13 on: December 15, 2010, 05:27:50 PM »

Wb6byu hello, I am using PL-259 silver with Phenolic Amphenol connectors. I soldered them. The center conductor is slightly visible I do that so I can see that it has not receded and is embedded in the solder at the connector end. The shielding is soldered at all four holes around the connector. anyway there are no faults with my antennas power supply etc. Update: I just witnessed the malfunction when connected to a 50 ohm dummy load so the problem has now been isolated down to the rig alone. The power dropped down from 100w to 2w pep yet the alc was intact and the swr was 1:0  If I wait a few minutes it recovers to 100 watts pep but drops back after transmitting for about 30 seconds.
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N4PSE
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Posts: 69




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« Reply #14 on: December 16, 2010, 03:20:23 PM »

Sounds similar to a problem I recently had with my ProIII. See my posting under this forum and under "mods and repairs" for 756ProIII output problems. Turned out to be a bad driver MOSFET. Not sure what the 718 uses, but that might give you another angle to look at.  Good luck, Jim
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