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Author Topic: IC-730 USB receive and transmit are 200 hz apart.  (Read 3557 times)
K4GVO
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Posts: 6


WWW

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« on: March 25, 2013, 05:45:00 AM »

AM and LSB are seeminging OK.  I didn't test cw. 

Any ideas on what might be  going on?  Is it something I'm going to be able to fix?  I have a counter but it's not real accurate and I have a Tek scope.  I don't have the service manual either, just the instruction manual.

Thanks,
Jim.
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KA4POL
Member

Posts: 1996




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« Reply #1 on: March 25, 2013, 06:43:54 AM »

You are not by any chance in split operation?
You can check the frequency by receiving WWV. That's certainly more accurate than your counter.
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W9GB
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Posts: 2623




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« Reply #2 on: March 25, 2013, 07:22:40 AM »

Icom manuals and schematics
courtesy of N7TGB (thank him for service)
http://www.n7tgb.net/pages/radio/icom_manuals.htm

Icom IC-730 Service Manual
http://www.download.n7tgb.net/Icom_Manuals/IC-730_service_manual.pdf
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AC2EU
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Posts: 403


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« Reply #3 on: March 25, 2013, 07:23:49 AM »

Does the display indicate the change when you key the mike?
Is RIT engaged?
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K4GVO
Member

Posts: 6


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« Reply #4 on: March 25, 2013, 08:51:29 AM »

Does the display indicate the change when you key the mike?
Is RIT engaged?

RIT is off.  The display does not change on transmit.  The receiver frequency is right on with wwv at 10 MHZ. I've owned this rig since 1982 and am fairly sure I know how to operate it.   Wink  I have a second receiver that I'm testing with.  I've confirmed that the IC-730 is transmitting on 28469.800 +- a few hz when the other receive is set to 28470 (USB) and is transmitting on 28470 on LSB.  It behaves the same on 40 meters.  I didn't check any other band. 

And thanks for the manuals links.

Thanks,
Jim.
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K4GVO
Member

Posts: 6


WWW

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« Reply #5 on: March 25, 2013, 08:52:55 AM »

You are not by any chance in split operation?
You can check the frequency by receiving WWV. That's certainly more accurate than your counter.
No, it's not split.  The other vfo is considerably different in frequency, in any case.

Jim.
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AC2EU
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Posts: 403


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« Reply #6 on: March 25, 2013, 11:36:30 AM »

OK ,inow that you have checked all of the obvious things and the display is not indicating the change, then the problem is limited to a drift in the USB section. Your VFO appears to be OK.

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K4GVO
Member

Posts: 6


WWW

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« Reply #7 on: March 25, 2013, 04:09:40 PM »

OK ,inow that you have checked all of the obvious things and the display is not indicating the change, then the problem is limited to a drift in the USB section. Your VFO appears to be OK.

Any suggestions as to which component(s)?  Perhaps a cap?  I don't have a maintenance harness so I'm guessing I'll have to debug statically unless it's on top. 

Thanks,
Jim.
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W9GB
Member

Posts: 2623




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« Reply #8 on: March 25, 2013, 05:36:33 PM »

Do you have the P.B. Tune (IF shift) control in the 12 o'clock (detent) position ?
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AC2EU
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Posts: 403


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« Reply #9 on: March 25, 2013, 08:52:17 PM »

OK ,inow that you have checked all of the obvious things and the display is not indicating the change, then the problem is limited to a drift in the USB section. Your VFO appears to be OK.

Any suggestions as to which component(s)?  Perhaps a cap?  I don't have a maintenance harness so I'm guessing I'll have to debug statically unless it's on top. 

Thanks,
Jim.

I don't know the specifics of that radio, but my conclusion is from the diagnostics that you presented here.
The USB section is where you need to look since everything else is OK, but only some good old fashioned troubleshooting will get it fixed. It could be something as mundane as a bad solder joint on a critical component for all I know...
Static analysis may not yield much, since it is only off frequency, not totally failed.
Is the USB carrier fully suppressed or do you get some carrier when keying up?

Perhaps someone on the forum who knows the radio may have some further insight for you.
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AD7WB
Member

Posts: 29




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« Reply #10 on: March 31, 2013, 09:51:47 PM »

Hi Jim,

See pages 8-4 and 8-5, BFO adjustment, in the service manual. USB, LSB receive and transmit are independent. The BFO's are just free-running oscillators, not synthesized from a master source so it could just be ageing of the crystals, I've seen ageing in my 730.

The most relevant parts are C40 and L2 on the detector board, page 9-8 of the service manual.

If you don't think your frequency counter is accurate align that first! A lot of frequency counters have a 10MHz output. Inside the counter will be a small variable cap next to the crystal. Adjust that cap after the counter warms up and zero beat the 10MHz output with WWV.

Good Luck,

Lance AD7WB
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