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New to the group, hoping to get some advice to get my little tuner going.

What I have is the typical Aliexpress kit, preloaded with 3.2.? I ordered the version that supplies SO-239 connectors and the Auto and Bypass switches.

It went together reasonably well.? The only assembly details that might be of note are:

• the Bypass and Auto connections to the bottom of the board were tough and I may have to revisit them.? Way too small for me to do confidently with a soldering iron. I ended up using two short lengths of the wire left over from the binocular transformer, with the ends cleaned up.
• I was supplied with 8 electrolytic capacitors.? There's only space for 6, so I assume I got two extra in error.? I've seen nothing to suggest they belong somewhere else, like the bottom of the board.
• No wires for connecting the SO-239 connectors were included.? I assumed that an inch or so of unshielded wire would be OK to make the connections to the board, rather than try to convince chunks of RG58 to do the contortions.? The connectors have short ground wires to the board as well.? I didn't run a wire between the two connectors, assuming that the board would do that.
• I didn't put capacitors across the Auto and Bypass switches, something I've seen mentioned while looking for answers (none included - I'm assuming the extra electrolytic caps weren't intended for this purpose?)
• I didn't use the center out of a piece of coax cable for the binocular transformer.? What I had was solid center conductor and kept breaking when I tried to bend it to the necessary shape.? I ended up using insulated stranded wire that *just* fit through the holes on the board.

It powers up.? The display shows Power, SWR, L and C as zeros.? There's a dot to the right of the power line to signify (I understand), Auto mode.? That all looks promising, but the behavior isn't.? I'm seeing a few things that don't seem right, which may or may not be connected.? In no particular order:

• Auto and Bypass switches don't seem to do anything.
• Powering up with the switches depressed doesn't seem to do anything.
• Tune button works as I believe it should - reset with quick press, Tune with longer push.
• When I put RF to the tuner, it makes all the snapping sounds one would expect, then shows an acceptable SWR on the display.
• Power on the display is crazy-high... suggesting my 10 watts is actually over 100 watts.
• Radio shows the same high SWR as without the tuner in line... unless I set the TX power up to maybe 20 watts... then it seems that the clicking and snapping results in something the radio likes.
• The Auto dot indicator will switch to the underscore mark instead, after tuning is complete.? I can't get the dot back unless I power cycle the tuner.
• Transmitting again, on the same frequency will sometimes result in the tuner trying to find a better result.? Sometimes it does, sometimes it ends up failing and the L and C values show as 0.
• When a match is found, the SWR indicated by the tuner might be 1.15:1, but the radio is reporting 1.75:1.? In some cases, the radio reports 'off the scale' while the tuner is indicating a good match.
• On 30m, I saw a match determined, but the SWR reported by the radio continued to rise with 20 watts continuing to the antenna.? This suggests a thermal issue in an inductor perhaps?

I'm at a loss as to what to try, where to look.? I suppose it's possible that there are a few issues at play here, so maybe the first place to check is at the Bypass and Auto connections on the bottom of the board.? I can feel the anxiety building though, just thinking about putting the iron to those spots again... ;-)

I spend some time looking for a procedure to follow to troubleshoot this tuner, but found nothing.

All suggestions appreciated!

73

Brock VA7AV

I'm guessing you may have damaged the auto and bypass switches while soldering. I did exactly that with my auto switch. I used magnet wire for the ground bus and overheated to burn off the insulation. I was able to rescue it by reheating the sunken terminal and pulling it out of the switch somewhat, though I'm on the lookout for better quality switches. Try disconnecting the wires from the switches and shorting them to ground manually.?

Your SWR and power readings are probably off due to the inferior Shottky RF-sensing diodes. Mine is also off (Ali-Express, Hisonauto). I ordered some 1N5711 diodes from Mouser. I'll have them early this week and I will post an update.

The Ali listing for my tuner claimed that it would tune down to 1 W. It seems to do that just fine using my KX3. I did not do the binocular transformer mod and programming change.

Brock,

Good information -any updates on your progress?
Still building mine - it came without switches. From the schematic it looks like they are all momentary switches, I hope I am correct. I also see that there is no power switch (on/off) listed in the schematic, but would be easy to include.

Hi Michael,

Yes, I can provide an update.

The seller offered to send me some replacement Schottky diodes, which eventually arrived.? They turned out to be axial diodes, not surface mount, so that was good to see.? The board actually has pads for non-surface mount diodes, so it was actually fairly easy to pop the original ones off the board and get the new larger ones in place.

However, that didn't solve the problem.? Although, I think the power reading is now more accurately inaccurate... I'd say it's closer to exactly 10x actual transmit power than it was before... LOL

I'm also noticing that when TX stops, it takes a short time for the display to return to 'receive' readings (0 W, 0 SWR).? If I transmit with 5 watts, it shows around 50 watts.? Then when TX shuts off, the display reads 50W, 17W, 5W, 0.5W, 0... as it seems to refresh.? Slowly enough that I can read all the decrementing numbers, but quick enough that it's probably less than 1.5 to 2 seconds in total.

I'm guessing there's a capacitor involved, maybe a bleed resistor, but I'm in no way competent enough to find where or confirm.? If the wrong value of either surface mount component was placed on the board, somewhere, by the board builder, I'm wondering if this would be possible.

While waiting for the diodes, I ended up ordering another ATU-100 kit from a different seller.? I built it also (easier the second time for sure!).? So far, it seems to function properly and the display certainly indicates what I think the correct power actually is.? Having done it twice, the same way, I have to think the original unit has a problem from the seller.? Unless there's a cold solder joint somewhere that I should be blamed for.? I'd be grateful if anyone who is familiar with the schematic and operation could suggest where to look.

The bypass and auto switches are indeed momentary.? The only tricky part is connecting wires to the underside of the board for these switches.? The pads are very small and there's no hole to help you out.? A steady hand and it's not too bad, just a bit of a pain.? I'm actually a bit surprised that the board isn't set up to allow for these connections with holes and larger pads.

73

Brock VA7AV

Thanks Brock.
Have the wires connected under the board for the Auto and Bypass switches - If I build another one, I think that I will find a different method to attach those.

Michael