/g/Icom-746Pro

Re: 746pro transmit problems on 17 and 15 meters only

biwa@... (Burt K6OQK) — Wed, 02 Apr 2025 15:11:54 -0700

I had a similar problem several years ago, coincidentally with my ICOM 746PRO. In my case it was on 40-Meters. It was getting into my wife's computer monitor as well as the TV sound system, and my workbench audio. My friend Steve, W6RHM, who is an EMC, EMI specialist suggested I put a Toroid core on the radio's A.C. line cord as close to the power supply as possible. I did and that completely solved the problem. As I recall, I used a 240-J Toroid, as I had several of those on hand. Looking at the back of the radio now, I see that I wound 5 turns of the power cord through the core.

The radio was looking for a better RF ground than what I was providing at the time. In its search it went looking back down the Mains, which in turn conducted the RF into many of the power spigots in our home.

For what it may be worth...

Burt, K6OQK

At 04:02 PM 4/1/2025, Kory Oldham W4RZ wrote:

Re: 746pro transmit problems on 17 and 15 meters only

brock71@... (John Brock) — Wed, 02 Apr 2025 08:14:37 -0700

Could it be you need a rf choke on the coax?

Re: 746pro transmit problems on 17 and 15 meters only

Kory@... (Kory Oldham W4RZ) — Tue, 01 Apr 2025 16:02:41 -0700

I have the same issue with my 160M and 80M dipole(s), I played with my grounding cables making them longer and shorter, I forget where I ended up but my RFI/EMI feeding back and knocking out my WIfi, Mouse, Keyboard etc.. went away for 90%. I am limited to 50 Watts'ish on 17m much more then that and the RFI/EMI starts backup again, but that is the only area now I have issues with.

I would say check your grounds, maybe try to lengthen them first them shorten them, it sounds like mine and was a ground loop kind of issue.

Kory

W4RZ

Re: 746pro transmit problems on 17 and 15 meters only

W4JFABob@... (Bob Naylor) — Tue, 01 Apr 2025 15:30:08 -0700

If it's working fine into a dummy load so working into a 50 ohm pure resistive,
or darn near, load, the radio is fine, so that leaves RF in the shack, connections, ground, ground wire length.

Bob W4JFA

Re: 746pro transmit problems on 17 and 15 meters only

kgaaba@... (kgaaba) — Tue, 01 Apr 2025 10:53:54 -0700

It actually works fine on a dummy load

Re: 746pro transmit problems on 17 and 15 meters only

qrq_cw@... (Mark Brueggemann K5LXP) — Tue, 01 Apr 2025 06:27:47 -0700

On Monday, March 31, 2025 at 03:53:30 PM MDT, kgaaba via groups.io <kgaaba@...> wrote:

When keying up on any mode this is what the meter reading says

What happens with a dummy load?

Mark K5LXP
Albuquerque, NM

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746pro transmit problems on 17 and 15 meters only

kgaaba@... (kgaaba) — Mon, 31 Mar 2025 14:53:29 -0700

It transmits and works fine on all other bands except 17 and 15. My antenna is fine and works well with other rigs. When keying up on any mode this is what the meter reading says. Any help is appreciated. Thanks Ken

The antenna tuner works fine

Re: service manual

merlin4670@... (Michael McGuirt) — Sun, 30 Mar 2025 06:34:47 -0700

Scott,

Can you send me a copu of the manual as well ?

Mac

K2TEC

Re: service manual

Sean2e0saf@... (sean M0OEG) — Sat, 29 Mar 2025 07:58:38 -0700

Thanks scott I will have a look

Re: service manual

Sean2e0saf@... (sean M0OEG) — Sat, 29 Mar 2025 07:58:18 -0700

The 746pro one is ok but the 746 one is blurred peter

Re: service manual

W1NB@... (Scott Madison) — Fri, 28 Mar 2025 12:02:33 -0700

Sean,

I sent an e-mail directly to you.

Scott, W1NB

Re: service manual

plaws0@... (Peter Laws) — Fri, 28 Mar 2025 11:57:33 -0700

The one in the files section here looks OK at first glance at least.

On Fri, Mar 28, 2025 at 2:40 PM sean M0OEG via groups.io
<Sean2e0saf@...> wrote:

would anyone have a good copy of the RF unit parts diagram please for the ic746 non pro the pro is a different layout

the ones i have found are terribly blurred.

thanks

--
Peter Laws | VE[23]UWY / N5UWY | plaws0 gmail com | Travel by Train!

Re: IC-746PRO 2M sensitivity?

Sean2e0saf@... (sean M0OEG) — Fri, 28 Mar 2025 11:56:01 -0700

hi donald i have only just got the radio it was bought with a dead tx output thats fixed..

i have looked at the id5100 spec

FM/NFM (Ham bands): 0.18 uV (12 dB SINAD)

icom 746 spec

FM (12 dB SINAD) 0.18 µV (144 MHz)*3 preamp on

so both should be the same or pretty much

i have found on the ctrl board Q5 split open its a S.fet 2sk515 T1B i have one here from icom to replace it.. however im not entirely sure of its function if anyone can tell..?

this is on the icom ic746 NON PRO

service manual

Sean2e0saf@... (sean M0OEG) — Fri, 28 Mar 2025 11:40:48 -0700

would anyone have a good copy of the RF unit parts diagram please for the ic746 non pro the pro is a different layout

the ones i have found are terribly blurred.

thanks

Re: IC-746PRO 2M sensitivity?

donhellen@... (Donald Hellen) — Wed, 26 Mar 2025 17:48:52 -0700

Sean,

Was the sensitivity the same before, or is this the first time you've checked?

I ask because the 5100 is a much newer radio and I would expect it to have
better sensitivity overall, though it might not be very well noticed.

Donald KX8K

On Wed, 26 Mar 2025 15:33:03 -0700, "sean M0OEG via groups.io"
<Sean2e0saf@...> wrote:

Thanks for that jim...

I will have a look at it ASAP..

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Re: IC-746PRO 2M sensitivity?

Sean2e0saf@... (sean M0OEG) — Wed, 26 Mar 2025 15:50:19 -0700

Thanks for that jim...

I will have a look at it ASAP..

If I put my id5100 on same frequency the 746 seems down on RX sensitivity.

If i put the Rx preamp on my linear amplifier the rx comes up somewhat.

So hopefully maybe it's that causing the issue.

Re: IC-746PRO 2M sensitivity?

barberaudio@... (James Barber) — Tue, 25 Mar 2025 20:28:22 -0700

Hi Sean,

Yes, it's a pre-biased PNP, DTA114EU.

In the PRO version the collector ties to the center of a network of 100K to ground and 100 ohms to the

anode of one of the PIN diodes in the dual package. I would imagine the non-PRO version is similar.

In my case the PNP was shorted, and replacing it fixed the 2M sensitivity issue. If your failure is identical you can check it in-circuit to be sure. My "short" was around 64 ohms E-C, assuming I remember correctly.

The fix was tedious. The more SMD repair I do on tightly-packed boards, the less inclined I am to do it. My wife also says I've grown cranky and tend to yell at children and other small rodents that invade my territory. ;-)

Hope that helps and 73,

Jim N7CXI

Re: IC-746PRO 2M sensitivity?

Sean2e0saf@... (sean M0OEG) — Tue, 25 Mar 2025 09:50:22 -0700

jim i have a 746 non pro and i seem to have a similar issue here..

Q604 on the PA board is this the device DTA114EUA T106

located adjacent to J601 connector going to the rf unit..?

thanks for any help sean M0OEG

Re: TX alignment: 1mV audio??

Rob@... (Rob Beckers (VA3BUA & PA3BUA)) — Wed, 12 Mar 2025 10:53:00 -0700

Can't quite read the letters in your attached image Jim, but in any event, the non "Plus" version doesn't quite have the 'upgrade' possibilities unfortunately. I believe it can be unlocked to the full 3.2 GHz bandwidth, you can have a look at the link and see if your model is covered. That's about it though.

Hadn't thought about using regular 50 Ohm attenuators. Neat trick!

-Rob-