ICOM M-802 not tuning

[geoffschultz]

I'm an engineer with 25 years of cruising and 60+K miles under the keel, and am quite good at debugging systems, but I can't figure out what's going on with my ICOM M-802 not tuning. The system consists of an M-802 radio with an AC-140 tuner and a Shakespeare 390 24' whip antenna (I have a carbon fiber mast with no standing rigging). We are currently in Guatemala.

I'm a network controller for the NW Caribbean net, and last year I had no problems transmitting to the rest of fleet. One day I found that my ICOM M-802 wouldn't tune, but I could hear Chris Parker's forecasts and other participants in the NW Caribbean net just fine. The cruising season was almost over, so I didn't pursue it.

Once I had BlueJacket hauled for hurricane season, I had the yard brush my Dynaplates until they were nice and clean, and I hoped that would solve the problem as they were quite encrusted with stuff. When I splashed this year, it was clear that it didn't. Yesterday I hoped to debug the problem, but walked away defeated.

The problem is that when I press the Tune button, the radio flashes TUNE and then turns to THRU. You can hear the tuner clicking away when I do this. I have a digital SWR meter, and inserted it between the radio and the antenna. I can see an SWR of 10+ when it tries to tune. I also moved the SWR meter to just before the tuner, with the same results.

In an attempt to solve this, I disconnected all of the PL-259 connectors, inspected and cleaned them. I also thoroughly cleaned all of the ground connections, replaced some, and reassembled with dielectric grease. I replaced the GTO-15 cable with a new one. The control connector at the tuner is nice and clean.

Now, here's the kicker. At one point when I inserted the SWR meter at the radio, it tuned at 6, 8, and 12 MHz frequencies. Thinking that I had solved the problem, I reloaded all of the stuff in the lazarette that contains the tuner, removed the SWR meter, and tested to make sure that everything was working. It wouldn't tune! I have carefully inspected the PL-259 connector at the radio, but it looks fine.

I'm lost! Any ideas?

-- Geoff

[S/V Illusion]

Have friends who live in Marlborough.

As to the radio, it’s hard to guess. Best strategy to eliminate the many possibilities, I’d start by putting a dummy load on the transceiver output first. Assuming the radio loads properly, insert the tuner to ensure it isn’t the problem. If good so far, it’s an antenna/feed line issue

[geoffschultz]

I'm not a radio guy (I just play one on TV), so I assume that a dummy load looks like an antenna to the radio and has a PL-259 female connector?


Now, where to find one in the Rio Dulce in Guatemala...

[S/V Illusion]

Originally Posted by geoffschultz

I'm not a radio guy (I just play one on TV), so I assume that a dummy load looks like an antenna to the radio and has a PL-259 female connector?


Now, where to find one in the Rio Dulce in Guatemala...

Sorry, I shouldn’t assume it’s a common term except among radio guys.
It’s any resistive 50ohm load capable of dissipating the heat from a 100w transmitter. Commercially made ones look like a 1gal can or rectangular box, both of which have a coax fitting tied to a 50ohm load with a method for heat dissipation.
More important, you can easily make one with a light fixture and a 100 w incandescent bulb which would serve the purpose of a dummy load in the absence of a real one.

Alternatively, borrow or buy a different antenna and coax sufficient to test the radio/tuner on it so as to eliminate your antenna as a possible cause.

[jordanbigel]

Originally Posted by geoffschultz

The problem is that when I press the Tune button, the radio flashes TUNE and then turns to THRU. You can hear the tuner clicking away when I do this. I have a digital SWR meter, and inserted it between the radio and the antenna. I can see an SWR of 10+ when it tries to tune. I also moved the SWR meter to just before the tuner, with the same results.
-- Geoff

I am no radio expert, but I experienced this exact symptom you describe above, last year.

I did most of the things you described also, except the SWR meter (though I did observe that SOME bands would tune and others would not - most would not). But the symptom of TUNE -> THRU, the tuner clicking but not tuning, is exactly what I was seeing.

Since my tuner was 22 years old and was an AT-130 (originally purchased and used with an IC-M710) I concluded it was bad and replaced it with the AT-140 (and the control cable going from the tuner to the radio since it used a different connector and I do not trust myself to make up those tiny-pin connectors) and all is well now.

If you have cleaned everything and it still won't tune, it seems like the tuner itself is a likely candidate.

[sv_pelagia]

Not an expert here, but:

Make a temporary wire antenna by stringing a wire from mast down to cockpit and connect to tuner. If this works (it tunes) then problem related to your existing attena whip and/or feed.

[Brian.D]

What interested me was placing a SWR meter between the radio and the tuner. When you did that, your tuner worked. But once removed and reconnected to tuner, it did not. That is kind of telling me you may have a bad ground or a bad center pin. Regardless, it might be the coax between the radio and the tuner. See if you can barrow a RF cable and swap it out with the one you have. See if that does something.

Connecting any kind of wire to a radio will allow the radio to receive. So you said you can hear other stations but can not tune the tuner. In this case, I suspect a bad ground in the RF cable between the radio and the tuner. A loss of the center conductor could cause no reception. Or a short between the center conductor and shield could cause issues at the radio, maybe cancelling out the tuning process.

A lot of tuners will actually tune when it receives a correct dose of RF such as 10 watts, even without control cables. The radio can be tricked into thinking it is connected to a tuner by using a 10K resistor at the control port on the radio. Read this posting on how to do it.

Good luck

[geoffschultz]

Originally Posted by sv_pelagia

Not an expert here, but:

Make a temporary wire antenna by stringing a wire from mast down to cockpit and connect to tuner. If this works (it tunes) then problem related to your existing attena whip and/or feed.

Can this be any kind of wire? Length? Could I use an extension cord?

[markcouz]

I had identical symptoms with IC 802 / AT140, I could hear the tuning attempts but then the 802 would default to THRU, bypassing the tuner and connecting directly to the antenna.

I managed to source a good used AT140, and after swapping out the system worked perfectly.

[geoffschultz]

Originally Posted by Brian.D

Connecting any kind of wire to a radio will allow the radio to receive. So you said you can hear other stations but can not tune the tuner. In this case, I suspect a bad ground in the RF cable between the radio and the tuner. A loss of the center conductor could cause no reception. Or a short between the center conductor and shield could cause issues at the radio, maybe cancelling out the tuning process.

Another test that I ran was checking the resistance between the ends of the cable. With the cable disconnected at both ends, it was an open circuit. Shorting one end showed a complete circuit. I don't remember what the resistance was, but I remember that read 0 until I cranked it up to 20K ohms.

[geoffschultz]

Originally Posted by S/V Illusion

More important, you can easily make one with a light fixture and a 100 w incandescent bulb which would serve the purpose of a dummy load in the absence of a real one.

I found a 100 watt incandescent bulb and simply touched the tip of the PL-259 to the center of the bulb and had the ground touching the screw-in part of the bulb. When I pressed Tune, it didn't glow, and the SWR was 6.4 vs 9.x with the antenna connected. I tried this at the transceiver and by the tuner with similar results.


Was this correct, and if so, what does it indicate?

[bill good]

What was the SWR meter readings? The last tuner unit that I repaired had a broken soldered joint at the aerial terminal inside the tuner intermittently making a connection because it had been turned by the owner disconnecting the lead to the aerial.Also there was a isolating block that prevents DC but passes RF so a multimeter will not show resistance thru this block. If there is one in your installation try removing it for a test.

Regards

[S/V Illusion]

Originally Posted by geoffschultz

I found a 100 watt incandescent bulb and simply touched the tip of the PL-259 to the center of the bulb and had the ground touching the screw-in part of the bulb. When I pressed Tune, it didn't glow, and the SWR was 6.4 vs 9.x with the antenna connected. I tried this at the transceiver and by the tuner with similar results.


Was this correct, and if so, what does it indicate?

That is the method. If there was any output above a few watts, the bulb would indicate it. Apparently, you saw no visual indication of brightness which means no output. Does your SWR meter indicate forward power level?

[Brian.D]

Originally Posted by geoffschultz

Another test that I ran was checking the resistance between the ends of the cable. With the cable disconnected at both ends, it was an open circuit. Shorting one end showed a complete circuit. I don't remember what the resistance was, but I remember that read 0 until I cranked it up to 20K ohms.

An end-to-end (meaning either center tip, or shield) should result in 0Ω. A test between center pin and shield should result in no reading at all, or like on most of my meters an OL (Open Line). Also wiggle the cable to see if there is an intermittent open somewhere.

Another test I do is will the connector twist if I were to hold the cable and try to turn the actual connector. If it does move then your ground is broken and maybe making intermittent contact. That is why I found it interesting that you had it working with the SWR meter in the path.

If worst comes to worst, put the SWR meter back in. If it starts working then leave it in until you can get some good test gear or additional cables. Better to have a temporary fix than nothing at all.

[bill good]

GeoffSchultz, Sorry, I tried to edit my comments but was called away & the 30Mins expired!! (1) Yes you can string up & use an extention lead as a temp "long wire aerial" with a length of dry rope as the insulator. (2) If you can hear the tuner trying to auto tune then some power is available. (3) The last HF unit I fixed was the connector under the aerial terminal being disconnected because the internal part of that connector had been turned & pulled off the soldered connection. (4) Check the connection from the dynaplate to the tuner earth as it is very important & is a part of the aerial system just like the whip or long wire. (5) On HF installations it is common to have a "black box" thing in the coax lead from the transmitter to the tuner unit which isolates the DC path but allows the RF to pass. It will show open circuit on a multimeter.

The SWR meter is something you need to know how to read. It will show the forward power V reflected power & is expressed as a ratio i.e. 3:1 as the least expected. Useful to show any change/fault after all is working. The dummy load test would come after these checks are done. It is used to confirm the level of the power out & a commercial unit provides a means of limiting radiation & interference to other users.
Regards Bill (Retired Comms tech)