[ICOM] Receive level dropping-rig or antenna system issues?

[John]

Hi ron,

Do you remember what the problem was with the 761 and 751A?

73 John AF5CC

On Mon, Mar 25, 2013 at 11:53 AM,  <bonddaleena at aol.com> wrote:
> John, did you check Icom's 'knowledge base'?
> This symptom is a very common one with the 761 and no doubt the 751A. I have a MKIIg and haven't noticed any problem, but it's virtually unused. I bought it for my motorhome which I no longer have.....
>
> ron
> N4UE
>
>
>
>
>
>
>
> -----Original Message-----
> From: John G. <af5cc at fidmail.com>
> To: ICOM Reflector <icom at mailman.qth.net>
> Sent: Sun, Mar 24, 2013 7:30 pm
> Subject: Re: [ICOM] Receive level dropping-rig or antenna system issues?
>
>
> Hi George,
>
> Thanks for the information. I had a similar problem recently with my 706.  I
> would key it and the radio would turn off.  Checking the fuse the a
> continuity checker made it look good, but replacing it with another fuse
> solved that problem.
> Still have the receive issue, though, even with the new fuse, and it has
> always made the correct power on transmit.
>
> 73 John AF5CC
> ----- Original Message -----
> From: "George Jones" <gjones04 at tampabay.rr.com>
> To: "ICOM Reflector" <icom at mailman.qth.net>
> Sent: Sunday, March 24, 2013 10:08 PM
> Subject: Re: [ICOM] Receive level dropping-rig or antenna system issues?
>
>
>> Recently I had a similar problem on my IC-706MKII mobile. The problem was
>> more noticeable on transmit rather on receive.  I have operated this
>> mobile for some time without experiencing any problems on a Hustler
>> antenna with separate coils for each band.  About a month ago I picked up
>> a LGG tuner at a local hamfest and installed it in the mobile. I switched
>> the antenna out to a 108-inch steel whip. The tuner worked with this
>> combination and no apparent problem for several weeks except it seemed to
>> take longer to tune on 20-meters. After many attempts to check into a net
>> on 40-meters I began to suspect a problem. My first response was to think
>> that the problem was with the tuner or new antenna combination.
>> After bypassing the tuner and switching the antenna back to the Hustler
>> with 40-meter coil, the problem persisted.
>>
>> Out came the test equipment. First I connected a Bird watt meter and dummy
>> load to the IC-706MKII, HF/6 antenna connecter. After keying up the radio
>> in the FM mode and checking each of the HF bands, I noted that the TX
>> power would barely register any output on the Bird's lowest setting.
>> Now my thoughts turned to a defective PA section on the IC-706MKII radio.
>> My previous thought that there may have been a problem with the tuner and
>> 108-inch whip combination was now confirmed and that I had damaged the PA
>> section with that antenna combination.
>>
>> Further test....  Out came my other IC-706MKIIG radio. After connecting
>> the second radio up the problem seem to be no better. In fact, the Bird
>> watt meter indicated the same problem.  This had me really scratching my
>> head!  I began to check the 12-volt line and noted that the voltage looked
>> good around +13.8 volts at the connector to the radio.  I even keyed the
>> IC-706MKIIG transmitter while monitoring the voltage at the connector. The
>> voltage drop noted looked to be in the normal range with only about 0.3
>> volts drop.
>>
>> Now with both radios on the bench in the house with an Astron 50 amp
>> supply connected, both radios produced rated power out on the Bird meter.
>> Back to the car to further check out power cable.  I connected a 12-volt,
>> 60-watt camper style light bulb to the power cable an immediately observed
>> the problem. The light bulb lit up very dimly. Using the light bulb for a
>> test instrument, I began  testing each connection along the power cable.
>> In my vehicle, an SUV, I have a #6 wire running from the battery to a
>> distribution block near where the radios are mounted. The #6 wire runs
>> through a cartridge fuse right at the battery tap. The light bulb
>> indicated a problem with the fuse. I replaced the defective fuse and now
>> both radios make rated power in the car.  Further test with the Bird meter
>> indicated that the tuner and 108-inch whip combination was working as
>> expected.
>>
>> What we learned from this experience is that the original fuse was
>> stressed in a manor that it would not fail until a heavy current was drawn
>> through it. A simple continuity check with an ohm meter shows the fuse to
>> be good. The voltage drop across the fuse with the bulb connected
>> indicated several volts drop. The digital volt meter alone did not provide
>> enough of a load to indicate the problem.
>>
>> George - W4AQR
>>
>> --------------------------------------------------
>> From: "Larry Young" <k4lxv at bellsouth.net>
>> Sent: Sunday, March 24, 2013 3:46 PM
>> To: "ICOM Reflector" <icom at mailman.qth.net>
>> Subject: Re: [ICOM] Receive level dropping-rig or antenna system issues?
>>
>>> John: It should be easy to determine if it is internal or external to the
>>> rig. When the  receive is normal, attach an external signal source to the
>>> antenna input and note its level on the S meter. When the receive level
>>> drops, reconnect the same signal source and again not the S meter level.
>>> If it is the same as before when good, then obviously you have some
>>> oxidation occurring somewhere in the antenna/feedline/balun path.
>>> Larry  K4LXV
>>>
>>>
>>> --- On Sun, 3/24/13, John G. <af5cc at fidmail.com> wrote:
>>>
>>> From: John G. <af5cc at fidmail.com>
>>> Subject: [ICOM] Receive level dropping-rig or antenna system issues?
>>> To: "ICOM Reflector" <icom at mailman.qth.net>
>>> Date: Sunday,
>>> March 24, 2013, 3:03 PM
>>>
>>> Here is a message I posted a few months ago about the receive level
>>> dropping off at times in my Icom 706 original:
>>>
>>> "I have noticed for the past few months that the receive seems to drop
>>> at times on certain bands-it started on 12m and now occurs on 15m as
>>> well. If you click the key or mic to quickly put it into transmit the
>>> receive comes back. To me this sounds like a dirty relay or one that is
>>> going bad"
>>>
>>> Now here are some additional details, it seems to be occurring on other
>>> bands as well. 17m at times, and was doing it on 30m last night. Someone
>>> suggested to me that it could be a problem in the antenna system as well.
>>> I did some checking this morning, and have determined that it isn't in
>>> the low pass filter, the MFJ tuner, or any jumper coaxes in the shack. It
>>> would have to be in the feedline going to the G5RV, or the balun there. I
>>> haven't had time to change out the coax run
>>> yet.
>>>
>>> I have also noticed that on 12m and 15m the receive will come back up by
>>> itself at times. Sometimes it is a quick drop down and come back several
>>> times in succession. Would a relay problem do this?
>>>
>>> So, with this latest information, what is the better guess as to the
>>> problem-in the rig or the antenna system?
>>>
>>> 73 John AF5CC
>>>
>>> ----
>>> Your Moderator: Dick Flanagan K7VC: icom-owner at mailman.qth.net
>>> Icom Users Net: Sundays, 1700Z, 14.316 MHz
>>> Icom FAQ: http://www.qsl.net/icom/
>>> To support QSL/QTH.net: http://www.qsl.net/donate.html
>>> ----
>>> Your Moderator: Dick Flanagan K7VC: icom-owner at mailman.qth.net
>>> Icom Users Net: Sundays, 1700Z, 14.316 MHz
>>> Icom FAQ: http://www.qsl.net/icom/
>>> To support QSL/QTH.net: http://www.qsl.net/donate.html
>>
>> ----
>> Your Moderator: Dick Flanagan K7VC: icom-owner at mailman.qth.net
>> Icom Users Net: Sundays, 1700Z, 14.316 MHz
>> Icom FAQ: http://www.qsl.net/icom/
>> To support QSL/QTH.net: http://www.qsl.net/donate.html
>
> ----
> Your Moderator: Dick Flanagan K7VC: icom-owner at mailman.qth.net
> Icom Users Net: Sundays, 1700Z, 14.316 MHz
> Icom FAQ: http://www.qsl.net/icom/
> To support QSL/QTH.net: http://www.qsl.net/donate.html
>
>
> ----
> Your Moderator: Dick Flanagan K7VC: icom-owner at mailman.qth.net
> Icom Users Net: Sundays, 1700Z, 14.316 MHz
> Icom FAQ: http://www.qsl.net/icom/
> To support QSL/QTH.net: http://www.qsl.net/donate.html