Icom AT-140 tuner with M802 HF radio (SSB) stopped tuning

[Daurin]

After over 3 years continuously reliable use around the world, our tuner has suddenly stopped tuning. Pressing "TUNE" yields expected clacking in transceiver and tuner, but always results in "THRU" tuning, regardless of frequency. Cleaned and replaced all external connections on tuner and tested continuity and voltages in control cables and coax between transceiver and tuner. Inside tuner clean and dry. No sign of any changes in counterpoise strapping or external HF antenna (backstay).

In control cable, I get 12.6 V in the 13.6 V (red) power wire; a drop from 12.9 V on the transceiver output. Bypassed control power to deliver between 13.2 - 13.4 V directly to the tuner, but no help. Key and Start wires carry 5 V when idle, dropping to millivolts when TUNE is pressed (though too briefly for my multimeter to measure more precisely).

We are part way across the Indian Ocean on our circumnavigation, currently in Rodrigues (near Mauritius) en route to South Africa. Our HF radio is our only lifeline to weather, nets, and email at sea. Any suggestions or recommendations would be greatly appreciated.

[GordMay]

Greetings and welcome aboard the CF, Daurin.

[Daurin]

Thank you. I've always found the site very useful, and once belonged, but on a now obsolete email address. Profile updates pending.

[SoonerSailor]

Have you measured D.C. resistance between the backstay and the tuner's output lug to ensure continuity there?

If that is OK, I would open up the AT140 and look for any discontinuities between the output lug and the circuit board. Any recent nearby lightning strikes?

[bluewatervet]

Excellent troubleshooting tack by Soonersailor. Also make sure the tuner 'case' ground connections are solid in the same manner. since a tuner is usually outdoors in the weather, slowly accumulated salt build-up can really mess things up....

[Robert Tilbury]

I have used a AT140 for many years , im a amateure radio operator , (VK2LOZ)
can you try switching from ssb to "am" and key the mic when pressing the tune button as this will drop a AM Carrier ,, let me know if this tunes the antenna and we can go from there ,
You can email if you like ,
vk2loz@gmail.com
regards
Rob

[Auspicious]

Originally Posted by Daurin

In control cable, I get 12.6 V in the 13.6 V (red) power wire; a drop from 12.9 V on the transceiver output. Bypassed control power to deliver between 13.2 - 13.4 V directly to the tuner, but no help. Key and Start wires carry 5 V when idle, dropping to millivolts when TUNE is pressed (though too briefly for my multimeter to measure more precisely).

That's what is supposed to happen. The Tune wire (sometimes labeled Start) tells the tuner it is time to begin tuning by being grounded. The Key wire tells the radio the tuner is ready and to transmit a low-power carrier for the tuner to use for tuning, also signaled by grounding.

Originally Posted by SoonerSailor

Have you measured D.C. resistance between the backstay and the tuner's output lug to ensure continuity there?

I suspect SoonerSailor is on the right track. Someone probably connected the GTO-15 transmission wire to the backstay with a hose clamp. Very bad practice. With time and vibration the wire strands part one by one and eventually only the rigging tape is holding the GTO-15 up. Remove the tape and inspect. GTO-15 is just heavily insulated 14 AWG wire. Strip the end of the wire and crimp on a large blue ring terminal. Clamp the GTO-15 to the backstay with a wire clip (like ranchers use for electric cattle fences; get a stainless steel version) and loop the ring terminal onto one of the legs of the clip securing with another nut. On that leg of the clip U-bolt there will be the clip, retaining nut, ring terminal, and another nut. Tape it over and you're done. Remove the tape ever couple of years and inspect.

[Daurin]

Thanks for all your replies. I wasn't notified they came in - will have to check settings, though at this bandwidth, it may have to wait.

Before posting here, I had gone over the system as suggested above. I had good continuity between the backstay and the tuner lug, but remade both connections anyway. The tuner is in a lazerette, so fairly dry, but I still remade the connections to the counterpoise and control wires. The inside of the tuner is clean and dry, and there is good continuity on the control wires from inside the tuner (on the board) to the plug at the tranceiver end of the control cable. The counterpoise has good continuity from the tuner to the transceiver, the ship's tanks, and the dynaplate, but all connections in the 3" copper ribbon were cleaned and remade anyway.

I tried tuning in all modes, including AM, with the same result.

No lightning strikes anywhere near us in many months.

Thanks again for your input, and I look forward to any other ideas you might suggest.

[Daurin]

I should add that when the problem first arose last week, we were on a particularly wet passage where sea water may have found the plug at the tuner end of the command cable. In fact, the delicate wires in the plug were badly corroded. Naturally, I started there by remaking those connections as per above.
Is it likely that a corroded connection in that plug caused damage within the tuner or transceiver while trying to tune or transmit?

[Auspicious]

Originally Posted by Daurin

Before posting here, I had gone over the system as suggested above.

Well phooey.

So you remade the GTO-15 wire to backstay connection?

Originally Posted by Daurin

Is it likely that a corroded connection in that plug caused damage within the tuner or transceiver while trying to tune or transmit?

No. It's all so simple. Either there is power to the tuner or not (and you already provided power directly). The "control" is so simple as to approach elegance - no data, just grounding.

It is possible that water wicked into the cable and one of two control wires corroded and has either parted or has deteriorated to the point that a resistance measurement (high impedance DVM) shows good but that the ground signal is not detected by the tuner or radio. *sigh* I dislike just changing things to have something to try, especially for someone who has supply chain challenges (my way of saying "Amazon doesn't deliver here").

Rereading your original post I have a question. If I understand the control firmware in the radio correctly the reason that THRU is displayed after a tuning attempt is high SWR after a time out period. When you try to transmit after a tuning attempt does the SWR indicator light on the display? You'll have to transmit in CW, AM, or FSK (or whistle into the mic in an SSB mode) to actually generate power.

I suspect that the radio and tuner are working and the tuner is unable to get a good match (consistent with my hose clamp diatribe). Can you borrow an SWR meter? That would give a very clear indication. You could also run 50 or 60' of known-good wire from the antenna lug on the tuner hauled up on a spare halyard. If that tunes you know you have an antenna problem. In that case I'd suspect internal corrosion in the GTO-15. If so, GTO-15 is heavily insulated 14 AWG wire. You can get it from anywhere that does neon sign installation as the same wire is used for neon sign power supplies. Regular 14 AWG will also work until you can get the right product.

[SoonerSailor]

I had similar problems when the wrong tuner was selected in the M802 setup menu. Just remembered that.

[ejs]

Hello,

Since you said that the tuner makes the appropriate clicking noises when you try to tune, I doubt it is the control cable. It could still be the ANTC wire that tells the 802 the state of tune but that is not likely since it is trying to tune based on hearing the relays clicking.

I have fixed several of these tuners with this same symptom and have found it was caused by the internal wire to the ground lug being loose. Unfortunately to fix you need to open the tuner by undoing 2 dozen bolts with nuts. The ground lug is just a bolt through the case with the internal wire on one end and the external on the outside. The outside one can feel tight even if the internal one is loose. I'd have a look at that.

Cheers, Eric

[Daurin]

Originally Posted by Auspicious

So you remade the GTO-15 wire to backstay connection?
...
It is possible that water wicked into the cable and one of two control wires corroded and has either parted or has deteriorated to the point that a resistance measurement (high impedance DVM) shows good but that the ground signal is not detected by the tuner or radio.
...
When you try to transmit after a tuning attempt does the SWR indicator light on the display?
...
Can you borrow an SWR meter?

Yes, I remade the GTO-15 to backstay connection, but I do that routinely and it is well aloft, so it was actually quite clean. I don't have a SS bull-clamp handy, so I used the old hose clamp method, but I like the clamp idea, and will certainly adopt it next time.

How many ohms is too much resistance between the transceiver and the tuner on the control (Key,Start) wires? I just beep-tested them from the board inside the tuner to the plug at the transceiver end, and then checked voltages with the unit on and tuning.

No SWR indicator when TXing. I will go up to the meteorological office here and see if they have an SWR meter I might borrow....

[Daurin]

Originally Posted by SoonerSailor

I had similar problems when the wrong tuner was selected in the M802 setup menu. Just remembered that.

Yep, checked that...though I couldn't think of how that could have changed settings on its own overnight. But at this stage, I'll try anything.

[Daurin]

Originally Posted by ejs

It could still be the ANTC wire...

Which one is that? Key or Start?

Originally Posted by ejs

I have fixed several of these tuners with this same symptom and have found it was caused by the internal wire to the ground lug being loose.

I did check that when I had the tuner open on the bench the other day, but considering your experience, I think I'll check it again.

Thanks again to all,
Dirk