[ICOM] 756 pro III noise
Gary P. Fiber
gfiber at comcast.net
Fri Oct 15 14:27:20 EDT 2010
Icom did use filament tape also known as Strapping tape. Most any good
tape will do however.
Good find, I have seen that happen in the shop but never gave it any
thought about it being the cause of your noise.
Gary K8IZ
On 10/15/2010 10:47 AM, Jaime Gomez wrote:
> Thanks to all who answered my request giving me their hints. I found 2 coax
> cables routed different than shown in the bottom view in the service manual
> and found one contact of the connecting tape between the top and bottom
> boards, the one that goes on the back left side, with signs of corrosion. I
> cleaned it while I can get a replacement tape.
> Now the radio is working OK, no more annoying noise....
> 73,
>
> Jim, HK1N
>
> On Thu, Oct 14, 2010 at 8:36 PM, Jim Hargrave<w5ifp at gvtc.com> wrote:
>
>
>> Jim,
>>
>> Sounds like perhaps the spectrum sweep generator as the source of the
>> noise.
>> I would suspect an open ground on one of the inter-connecting cables /
>> coax,
>> causing it to radiate.
>>
>> 73's Jim
>> W5IFP
>>
>>
>>> -----Original Message-----
>>> From: icom-bounces at mailman.qth.net
>>> [mailto:icom-bounces at mailman.qth.net]On Behalf Of Jaime Gomez
>>>
>> > Sent: Thursday, October 14, 2010 6:36 PM
>>
>>> To: ICOM Reflector
>>> Subject: Re: [ICOM] 756 pro III noise
>>>
>>>
>>> I have made some more checkings and found these 2 issues:
>>>
>>> 1- The noise is produced by the Spectrum Scope. If I turn it off the
>>>
>> noise
>>
>>> desappears and also the noise changes pitch by changing the spectrum
>>>
>> span.
>>
>>> The S3LO signal is clean as I checked with my scope.
>>>
>>> 2- When I turn the radio on, I can hear signals and noticed that the
>>>
>> radio
>>
>>> is scanning, eventhough the scan is turned off. If I turn the
>>> main dial the
>>> scanning stops and the receiver dies, I cannot hear any signal at all, no
>>> matter which antenna port is selected or which VFO a or B is
>>> selected, seems
>>> like the antenna is disconnected from the radio.
>>>
>>> Will keep going tomorrow, I think this is not an easy one...
>>>
>>> 73, Jim, HK1N
>>>
>>> On Thu, Oct 14, 2010 at 3:11 PM, Frank A. Ellis
>>> <w3uhf.frank at gmail.com>wrote:
>>>
>>>
>>>> Jim,
>>>>
>>>> While this result may seem intuitive, don't forget that when
>>>>
>>> the LO power
>>>
>>>> is removed from a mixer, very little to no signal will appear
>>>>
>>> at the output
>>>
>>>> (IF port) of the mixer. The little power that will appear there
>>>>
>>> will consist
>>>
>>>> of the RF signal applied to the RF port, attenuated by the mixer's
>>>>
>> RF-IF
>>
>>>> port isolation, which could be in the 30-40dB range. Whatever power is
>>>> passed through the mixer, in this fashion, severely attenuated, will
>>>> certainly be well out of the frequency range that the
>>>>
>>> subsequent IF stages
>>>
>>>> are designed to process.
>>>>
>>>> So - don't rule out the possibility that the signal appearing at the RF
>>>> port of the mixer is actually the "dirty" signal, and you are
>>>>
>>> disabling it
>>>
>>>> from being processed in the mixer by removing the LO power. A spectrum
>>>> analyzer would be pretty valuable in verifying the cleanliness of all
>>>> signals being presented to the mixer.
>>>>
>>>> Just one more thought, without me looking it up, is J211 an "LO only"
>>>> connector, or is the LO signal just one of the signals carried
>>>>
>>> through this
>>>
>>>> connector? If this connector is carrying multiple lines, you
>>>>
>>> could also be
>>>
>>>> disabling something else by disconnecting it, leading to a possible red
>>>> herring.
>>>>
>>>> 73, good luck, and keep us posted on your findings!
>>>>
>>>> Frank, W3UHF
>>>>
>>>>
>>>>
>>>>
>>>> On Oct 14, 2010, at 11:10 AM, Jaime Gomez wrote:
>>>>
>>>>
>>>>> Thanks to all who have answered my request for help. I opened
>>>>>
>>> the radio
>>>
>>>> and
>>>>
>>>>> so far what I have found is that if I disconnect the cable at
>>>>>
>>> J211 in the
>>>
>>>>> main board, which carries the signal from 3LO the noise dissapears.
>>>>>
>> It
>>
>>>> looks
>>>>
>>>>> like something in the VCO card is causing the noise.
>>>>> Any other hints?
>>>>> Thank you,
>>>>>
>>>>> Jim, HK1N
>>>>>
>>>>> On Wed, Oct 13, 2010 at 2:47 PM, Alex<alex at kr1st.com> wrote:
>>>>>
>>>>>
>>>>>> Hi Jim,
>>>>>>
>>>>>> This sounds suspiciously like some cable became disconnected
>>>>>>
>>> from a PCB,
>>>
>>>>>> and
>>>>>> is perhaps now close to the CPU board or even touching it. Possibly
>>>>>>
>> a
>>
>>>> cable
>>>>
>>>>>> that connects to the PA board. Very wild guess without looking at
>>>>>>
>> the
>>
>>>>>> transceiver. :)
>>>>>>
>>>>>> I don't have any experience with this, but I found a similar problem
>>>>>>
>>>> with a
>>>>
>>>>>> FT-897. The problem was that I could hear a noise on 70cm
>>>>>>
>>> every time I
>>>
>>>>>> turned the dial. What I ended up doing was rerouting the small coax
>>>>>>
>>>> cable
>>>>
>>>>>> that came from the RX/TX board and connected to the PA board
>>>>>>
>>> away from
>>>
>>>> the
>>>>
>>>>>> front panel. The noise was then substantially less.
>>>>>>
>>>>>> So it may not be something terribly complicated what is
>>>>>>
>>> wrong with your
>>>
>>>>>> radio.
>>>>>>
>>>>>> I hope this helps somewhat.
>>>>>>
>>>>>> 73,
>>>>>> --Alex KR1ST
>>>>>> http://www.kr1st.com
>>>>>> http://www.airlinkexpress.org
>>>>>>
>>>>>>
>>>>>> -----Original Message-----
>>>>>> From: icom-bounces at mailman.qth.net
>>>>>>
>>> [mailto:icom-bounces at mailman.qth.net
>>>
>>>> ]
>>>>
>>>>>> On
>>>>>> Behalf Of Jaime Gomez
>>>>>> Sent: Wednesday, October 13, 2010 2:36 PM
>>>>>> To: ICOM Reflector
>>>>>> Subject: Re: [ICOM] 756 pro III noise
>>>>>>
>>>>>> Well, I did the reset, as per Walt's instructions. Same thing, no
>>>>>>
>> Tx,
>>
>>>>>> popping noise on all frequencies, not affected by the noise blanker,
>>>>>>
>>>> AGC,
>>>>
>>>>>> filters, etc....and now I noticed something else, when I
>>>>>>
>>> turn the dial,
>>>
>>>> the
>>>>
>>>>>> popping increases and depends of the dial turning
>>>>>>
>>> speed....Obviously the
>>>
>>>>>> auto tuner is not working because there is no rf to excite it....
>>>>>>
>>>>>> What can I look at, if there is anything?
>>>>>>
>>>>>> 73, Jim, HK1N
>>>>>>
>>>>>> On Wed, Oct 13, 2010 at 12:36 PM, Walt Heilsnis - WB2VSJ<
>>>>>> wb2vsj at earthlink.net> wrote:
>>>>>>
>>>>>>
>>>>>>> This is beginning to sound a little bit familiar - I
>>>>>>>
>>> vaguely remember
>>>
>>>>>>> something somewhere about a transmit issue like this and I
>>>>>>>
>>> think it was
>>>
>>>>>>> Auto-Tuner related.
>>>>>>>
>>>>>>> Anyway, according to the PRO III Manual the reset procedure is:
>>>>>>>
>>>>>>> - Make sure the transceiver power is OFF.
>>>>>>> - While pushing [M-CL] and [(F-INP)ENT], push
>>>>>>> [POWER] to turn power ON.
>>>>>>> - The internal CPU is reset.
>>>>>>> - A/D convertor calibration of the DSP unit starts and it
>>>>>>> takes 10 sec.
>>>>>>> - The transceiver displays its initial VFO frequencies when
>>>>>>> resetting is complete.
>>>>>>> - Correct the set mode settings after resetting, if desired.
>>>>>>>
>>>>>>> I have a PRO II and have not had any issues like this (yet) :)
>>>>>>>
>>>>>>> Walt
>>>>>>>
>>>>>>>
>>>>>>> -----Original Message-----
>>>>>>>
>>>>>>>> From: Jaime Gomez<cwdx.hk1n at gmail.com>
>>>>>>>> Sent: Oct 13, 2010 1:07 PM
>>>>>>>> To: ICOM Reflector<icom at mailman.qth.net>
>>>>>>>> Subject: Re: [ICOM] 756 pro III noise
>>>>>>>>
>>>>>>>> Hi Walt, I have connected a dummy load to the antenna terminal, no
>>>>>>>>
>>>>>> change,
>>>>>>
>>>>>>>> noise is present in all bands, all modes, not affected by
>>>>>>>>
>>> attenuators
>>>
>>>> or
>>>>
>>>>>>>> preamps, all other radios in the station (7800, proII, proIII,
>>>>>>>>
>> 781)
>>
>>>> work
>>>>
>>>>>>>> fine. I just noticed also that it is not transmitting, the Tx red
>>>>>>>>
>>>> light
>>>>
>>>>>>> just
>>>>>>>
>>>>>>>> blinks and turns off and no power output.
>>>>>>>>
>>>>>>>> How do I hard reset the rig to factory fresh as Rich sugested?
>>>>>>>>
>>>>>>>> Thanks, 73
>>>>>>>>
>>>>>>>>
>>>>>>> ----
>>>>>>> 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
>>>>>>>
>>>>>>>
>>>>>>
>>>>>>
>>>>>> --
>>>>>> Jim, HK1N
>>>>>> ----
>>>>>> 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
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> Jim, HK1N
>>>>> ----
>>>>> 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
>>>>>
>>>> 73, Frank A. Ellis, W3UHF
>>>>
>>>>
>>>>
>>>> ----
>>>> 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
>>>>
>>>>
>>>
>>>
>>> --
>>> Jim, HK1N
>>> ----
>>> 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
>>
>>
>
>
>
--
Gary P. Fiber K8IZ
Electronic Communications Systems Technician - Field
General Radio Telephone Operators License PG-19-6691,
with Shipboard Radar Endorsement.
Washington State Resident.
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