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Re: IC-751A vs IC-751 (was: distorted audio on 40 only)

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  • adb1x1
    Pete, The 751A does have the same VCO and electrolytics issues (I have the A version as well), but I have noticed that there was some changes in the parts
    Message 1 of 5 , Sep 10, 2006
    • 0 Attachment
      Pete,
      The 751A does have the same VCO and electrolytics issues (I have
      the A version as well), but I have noticed that there was some
      changes in the parts layout on the PLL board and quite a few changes
      on the main board, so that the electrolytic caps aren't as near the
      heatsink, so they probably won't go a quickly in the 751A.

      Though I haven't changed them yet, it looks like the VCO caps are
      the same type used in the 751. When I first got this one, it needed
      some alignment. When it came time to adjust these trimmers they were
      tight and felt a little sticky. I suspect there's a little bee's wax
      on them, so I'm sure I'll be replacing them soon.

      Anthony

      --- In Icom751@yahoogroups.com, Peter Jordahl <PJORDAHL@...> wrote:
      >
      > I have an IC-751A. Does anyone know whether any of the problems
      > mentioned below were fixed in the revisions made to produce the -A
      > model? I had a plain 751 before the 751A (the 751 was stolen!) and
      had
      > problems with a noisy synthesizer (possibly picking up some noise
      from
      > the PS-35 internal PS) and can't remember for sure if the
      disappearing
      > display was on the 751 or the 751A. I have an external PS for the
      > 751A! Apparently ICOM used a similar type of trimmer capacitor in
      all
      > their models of that era, because now my IC-970 is exhibiting
      problems
      > in the UHF side where the synthesizer won't lock and I have heard
      of
      > similar problems in the IC-475.
      >
      > I have since upgraded to a 756 PRO II, but like to keep the 751A
      going
      > as a backup radio.
      >
      > Pete K5GM
      >
      >
      > Icom751@yahoogroups.com wrote:
      >
      > >There are 4 messages in this issue.
      > >
      > >Topics in this digest:
      > >
      > >1a. Re: distorted audio on 40 only
      > > From: adb1x1
      > >1b. Re: distorted audio on 40 only
      > > From: adb1x1
      > >1c. Re: distorted audio on 40 only
      > > From: johnon40
      > >1d. Re: distorted audio on 40 only
      > > From: Jerry Plemmons
      > >
      > >
      > >Messages
      >
      >_____________________________________________________________________
      ___
      > >
      > >1a. Re: distorted audio on 40 only
      > > Posted by: "adb1x1" adb1x1@... adb1x1
      > > Date: Fri Sep 8, 2006 7:19 am (PDT)
      > >
      > >
      > > It sounds like the VCO trimmer for that band. A well known
      issue
      > >with the 751. You might get by by turning the trimmer several
      times and
      > >the realigning, but replacement is much better.
      > >
      > > There are 4 plastic trimmers in the VCO and all of them should
      > >probably be replaced at one time. It's not difficult, just getting
      the
      > >heavy shield off is a bit tedious - takes a fairly high wattage
      > >soldering gun (I used a 150 watt weller and it did ok) and a
      little
      > >care.
      > >
      > > Malcom Technical Services
      > >(http://www.angelfire.com/biz2/mts/updates.html) has good info on
      > >removing this 'box' and realigning the VCO trimmers - just
      requires a
      > >DVM basically.
      > >
      > > Go here and do a search on 751:
      > >http://www.icomamerica.com/support/kb/Default.aspx
      > >
      > > There are several articles that list issues with the 751. They
      cover
      > >the other issue you mention (Display). Basically there are some
      real
      > >problems with heat in the 751. Electrolytics don't like the heat
      and
      > >dry up. The DC-DC converter is especially bad; there are several
      in
      > >that section that will need to be replaced. Also there are several
      on
      > >the PLL board that are mounted near the heatsick that probably
      need to
      > >be replaced as well.
      > >
      > > I basically ordered all the 'problem' capacitors listed in these
      Icom
      > >articles and replaced them, however I used high temperature
      tandalums
      > >instead of aluminum electrolytics. The larger value tandulums are
      more
      > >expensive but are not as heat sensitve as the originals. I
      selected
      > >capacitors with higher voltage ratings than the originals (where
      > >available) since voltage handling is derated considerably with
      heat. I
      > >also replaced the trimmer resistor on the PLL board with a low
      noise
      > >fixed resistor as one of these articles suggests.
      > >
      > > All parts were ordered from Mouser.
      > >
      > > The DC-DC converter is a bit of a pain. It requires removal of
      all
      > >the knobs and front panel and a litle juggling of the display
      board,
      > >but it's not too bad.
      > >
      > >Anthony
      > >
      > >--- In Icom751@yahoogroups.com, "johnon40" <johnon40@> wrote:
      > >
      > >
      > >>My work horse radio has been my Icom 751 since I was licensed.
      > >>Lately, the audio has been notably distorted on 40. It's
      possible
      > >>that my transmit on 40 may be as well. I haven't been able to
      > >>
      > >>
      > >confirm
      > >
      > >
      > >>transmit distortion. The other bands are ok, but I've wondered
      about
      > >>on 80. Any clues as what is wrong with it or how to fix it? The
      > >>
      > >>
      > >only
      > >
      > >
      > >>other thing I've had wrong with this radio is that once in a
      while
      > >>when turning on the power, there is no frequency display; only
      dots.
      > >>Turning off, then back on has brought the display up every time.
      > >>
      > >>
      > >>
      > >
      > >
      > >
      > >
      > >
      > >
      > >
      >
    • adb1x1
      Pete, The 751A does have the same VCO and electrolytics issues (I have the A version as well), but I have noticed that there was some changes in the parts
      Message 2 of 5 , Sep 10, 2006
      • 0 Attachment
        Pete,
        The 751A does have the same VCO and electrolytics issues (I have
        the A version as well), but I have noticed that there was some
        changes in the parts layout on the PLL board and quite a few changes
        on the main board, so that the electrolytic caps aren't as near the
        heatsink, so they probably won't go a quickly in the 751A.

        Though I haven't changed them yet, it looks like the VCO caps are
        the same type used in the 751. When I first got this one, it needed
        some alignment. When it came time to adjust these trimmers they were
        tight and felt a little sticky. I suspect there's a little bee's wax
        on them, so I'm sure I'll be replacing them soon.

        Anthony

        --- In Icom751@yahoogroups.com, Peter Jordahl <PJORDAHL@...> wrote:
        >
        > I have an IC-751A. Does anyone know whether any of the problems
        > mentioned below were fixed in the revisions made to produce the -A
        > model? I had a plain 751 before the 751A (the 751 was stolen!) and
        had
        > problems with a noisy synthesizer (possibly picking up some noise
        from
        > the PS-35 internal PS) and can't remember for sure if the
        disappearing
        > display was on the 751 or the 751A. I have an external PS for the
        > 751A! Apparently ICOM used a similar type of trimmer capacitor in
        all
        > their models of that era, because now my IC-970 is exhibiting
        problems
        > in the UHF side where the synthesizer won't lock and I have heard
        of
        > similar problems in the IC-475.
        >
        > I have since upgraded to a 756 PRO II, but like to keep the 751A
        going
        > as a backup radio.
        >
        > Pete K5GM
        >
        >
        > Icom751@yahoogroups.com wrote:
        >
        > >There are 4 messages in this issue.
        > >
        > >Topics in this digest:
        > >
        > >1a. Re: distorted audio on 40 only
        > > From: adb1x1
        > >1b. Re: distorted audio on 40 only
        > > From: adb1x1
        > >1c. Re: distorted audio on 40 only
        > > From: johnon40
        > >1d. Re: distorted audio on 40 only
        > > From: Jerry Plemmons
        > >
        > >
        > >Messages
        >
        >_____________________________________________________________________
        ___
        > >
        > >1a. Re: distorted audio on 40 only
        > > Posted by: "adb1x1" adb1x1@... adb1x1
        > > Date: Fri Sep 8, 2006 7:19 am (PDT)
        > >
        > >
        > > It sounds like the VCO trimmer for that band. A well known
        issue
        > >with the 751. You might get by by turning the trimmer several
        times and
        > >the realigning, but replacement is much better.
        > >
        > > There are 4 plastic trimmers in the VCO and all of them should
        > >probably be replaced at one time. It's not difficult, just getting
        the
        > >heavy shield off is a bit tedious - takes a fairly high wattage
        > >soldering gun (I used a 150 watt weller and it did ok) and a
        little
        > >care.
        > >
        > > Malcom Technical Services
        > >(http://www.angelfire.com/biz2/mts/updates.html) has good info on
        > >removing this 'box' and realigning the VCO trimmers - just
        requires a
        > >DVM basically.
        > >
        > > Go here and do a search on 751:
        > >http://www.icomamerica.com/support/kb/Default.aspx
        > >
        > > There are several articles that list issues with the 751. They
        cover
        > >the other issue you mention (Display). Basically there are some
        real
        > >problems with heat in the 751. Electrolytics don't like the heat
        and
        > >dry up. The DC-DC converter is especially bad; there are several
        in
        > >that section that will need to be replaced. Also there are several
        on
        > >the PLL board that are mounted near the heatsick that probably
        need to
        > >be replaced as well.
        > >
        > > I basically ordered all the 'problem' capacitors listed in these
        Icom
        > >articles and replaced them, however I used high temperature
        tandalums
        > >instead of aluminum electrolytics. The larger value tandulums are
        more
        > >expensive but are not as heat sensitve as the originals. I
        selected
        > >capacitors with higher voltage ratings than the originals (where
        > >available) since voltage handling is derated considerably with
        heat. I
        > >also replaced the trimmer resistor on the PLL board with a low
        noise
        > >fixed resistor as one of these articles suggests.
        > >
        > > All parts were ordered from Mouser.
        > >
        > > The DC-DC converter is a bit of a pain. It requires removal of
        all
        > >the knobs and front panel and a litle juggling of the display
        board,
        > >but it's not too bad.
        > >
        > >Anthony
        > >
        > >--- In Icom751@yahoogroups.com, "johnon40" <johnon40@> wrote:
        > >
        > >
        > >>My work horse radio has been my Icom 751 since I was licensed.
        > >>Lately, the audio has been notably distorted on 40. It's
        possible
        > >>that my transmit on 40 may be as well. I haven't been able to
        > >>
        > >>
        > >confirm
        > >
        > >
        > >>transmit distortion. The other bands are ok, but I've wondered
        about
        > >>on 80. Any clues as what is wrong with it or how to fix it? The
        > >>
        > >>
        > >only
        > >
        > >
        > >>other thing I've had wrong with this radio is that once in a
        while
        > >>when turning on the power, there is no frequency display; only
        dots.
        > >>Turning off, then back on has brought the display up every time.
        > >>
        > >>
        > >>
        > >
        > >
        > >
        > >
        > >
        > >
        > >
        >
      • Ray
        I have been told there are quite a few differences in the 751 and the 751A. Also the 751A was the proto type of the 761. Plus they added the built in UX-14 and
        Message 3 of 5 , Sep 10, 2006
        • 0 Attachment
          I have been told there are quite a few differences in the 751 and the 751A.
          Also the 751A was the proto type of the 761. Plus they added the built in
          UX-14 and AT-150 antenna tuner for example.
          I have both here now and wouldn't get rid of either (maybe for enough
          money ).
          My 761 is completely stock. The 751A has a 250 cycle filter added. Fantastic
          for CW and RTTY !! I have opened it up for full transmit. The 60 meter band
          works beautiful in it. My came configured for IF shift. Changed it back to
          PBT. Yes, PBT is much better. I use both radios to drive a little modified
          AL-811 amp. Does it perform ?? How does 336/336 sound. Still need BS7H. 291
          RTTY.

          Any mods or eminence that I didn't feel comfortable doing has all been
          perform by Scott Malcom at MTS. VCO mods, etc. His work is perfect and
          prices very reasonable.

          Hang on to your 751A. It will give you many years of service.

          73 and DX to you.



          Raymond H. McClure - W8CNL
          5 McKenzie Circle
          North Augusta, S.C.
          29841-4319

          Meddle not in the Affairs of Dragons, for Thou Art Crunchy and Taste Good
          with Catsup or BBQ Sauce

          * * * * * * * * * * * * * * * * * * * * * * * *


          ----- Original Message -----
          From: "adb1x1" <adb1x1@...>
          To: <Icom751@yahoogroups.com>
          Sent: Sunday, September 10, 2006 10:30 AM
          Subject: [Icom751] Re: IC-751A vs IC-751 (was: distorted audio on 40 only)


          > Pete,
          > The 751A does have the same VCO and electrolytics issues (I have
          > the A version as well), but I have noticed that there was some
          > changes in the parts layout on the PLL board and quite a few changes
          > on the main board, so that the electrolytic caps aren't as near the
          > heatsink, so they probably won't go a quickly in the 751A.
          >
          > Though I haven't changed them yet, it looks like the VCO caps are
          > the same type used in the 751. When I first got this one, it needed
          > some alignment. When it came time to adjust these trimmers they were
          > tight and felt a little sticky. I suspect there's a little bee's wax
          > on them, so I'm sure I'll be replacing them soon.
          >
          > Anthony
          >
          > --- In Icom751@yahoogroups.com, Peter Jordahl <PJORDAHL@...> wrote:
          >>
          >> I have an IC-751A. Does anyone know whether any of the problems
          >> mentioned below were fixed in the revisions made to produce the -A
          >> model? I had a plain 751 before the 751A (the 751 was stolen!) and
          > had
          >> problems with a noisy synthesizer (possibly picking up some noise
          > from
          >> the PS-35 internal PS) and can't remember for sure if the
          > disappearing
          >> display was on the 751 or the 751A. I have an external PS for the
          >> 751A! Apparently ICOM used a similar type of trimmer capacitor in
          > all
          >> their models of that era, because now my IC-970 is exhibiting
          > problems
          >> in the UHF side where the synthesizer won't lock and I have heard
          > of
          >> similar problems in the IC-475.
          >>
          >> I have since upgraded to a 756 PRO II, but like to keep the 751A
          > going
          >> as a backup radio.
          >>
          >> Pete K5GM
          >>
          >>
          >> Icom751@yahoogroups.com wrote:
          >>
          >> >There are 4 messages in this issue.
          >> >
          >> >Topics in this digest:
          >> >
          >> >1a. Re: distorted audio on 40 only
          >> > From: adb1x1
          >> >1b. Re: distorted audio on 40 only
          >> > From: adb1x1
          >> >1c. Re: distorted audio on 40 only
          >> > From: johnon40
          >> >1d. Re: distorted audio on 40 only
          >> > From: Jerry Plemmons
          >> >
          >> >
          >> >Messages
          >>
          >>_____________________________________________________________________
          > ___
          >> >
          >> >1a. Re: distorted audio on 40 only
          >> > Posted by: "adb1x1" adb1x1@... adb1x1
          >> > Date: Fri Sep 8, 2006 7:19 am (PDT)
          >> >
          >> >
          >> > It sounds like the VCO trimmer for that band. A well known
          > issue
          >> >with the 751. You might get by by turning the trimmer several
          > times and
          >> >the realigning, but replacement is much better.
          >> >
          >> > There are 4 plastic trimmers in the VCO and all of them should
          >> >probably be replaced at one time. It's not difficult, just getting
          > the
          >> >heavy shield off is a bit tedious - takes a fairly high wattage
          >> >soldering gun (I used a 150 watt weller and it did ok) and a
          > little
          >> >care.
          >> >
          >> > Malcom Technical Services
          >> >(http://www.angelfire.com/biz2/mts/updates.html) has good info on
          >> >removing this 'box' and realigning the VCO trimmers - just
          > requires a
          >> >DVM basically.
          >> >
          >> > Go here and do a search on 751:
          >> >http://www.icomamerica.com/support/kb/Default.aspx
          >> >
          >> > There are several articles that list issues with the 751. They
          > cover
          >> >the other issue you mention (Display). Basically there are some
          > real
          >> >problems with heat in the 751. Electrolytics don't like the heat
          > and
          >> >dry up. The DC-DC converter is especially bad; there are several
          > in
          >> >that section that will need to be replaced. Also there are several
          > on
          >> >the PLL board that are mounted near the heatsick that probably
          > need to
          >> >be replaced as well.
          >> >
          >> > I basically ordered all the 'problem' capacitors listed in these
          > Icom
          >> >articles and replaced them, however I used high temperature
          > tandalums
          >> >instead of aluminum electrolytics. The larger value tandulums are
          > more
          >> >expensive but are not as heat sensitve as the originals. I
          > selected
          >> >capacitors with higher voltage ratings than the originals (where
          >> >available) since voltage handling is derated considerably with
          > heat. I
          >> >also replaced the trimmer resistor on the PLL board with a low
          > noise
          >> >fixed resistor as one of these articles suggests.
          >> >
          >> > All parts were ordered from Mouser.
          >> >
          >> > The DC-DC converter is a bit of a pain. It requires removal of
          > all
          >> >the knobs and front panel and a litle juggling of the display
          > board,
          >> >but it's not too bad.
          >> >
          >> >Anthony
          >> >
          >> >--- In Icom751@yahoogroups.com, "johnon40" <johnon40@> wrote:
          >> >
          >> >
          >> >>My work horse radio has been my Icom 751 since I was licensed.
          >> >>Lately, the audio has been notably distorted on 40. It's
          > possible
          >> >>that my transmit on 40 may be as well. I haven't been able to
          >> >>
          >> >>
          >> >confirm
          >> >
          >> >
          >> >>transmit distortion. The other bands are ok, but I've wondered
          > about
          >> >>on 80. Any clues as what is wrong with it or how to fix it? The
          >> >>
          >> >>
          >> >only
          >> >
          >> >
          >> >>other thing I've had wrong with this radio is that once in a
          > while
          >> >>when turning on the power, there is no frequency display; only
          > dots.
          >> >>Turning off, then back on has brought the display up every time.
          >> >>
          >> >>
          >> >>
          >> >
          >> >
          >> >
          >> >
          >> >
          >> >
          >> >
          >>
          >
          >
          >
          >
          >
          >
          >
          > Yahoo! Groups Links
          >
          >
          >
          >
          >
          >
          >
          >
          >
          >
          >
        • Peter Jordahl
          Ray and Anthony, Thanks for your comments. I believe I will not anticipate problems before they occur. The re-placement of components in the A-model sounds
          Message 4 of 5 , Sep 11, 2006
          • 0 Attachment
            Ray and Anthony,
            Thanks for your comments. I believe I will not anticipate problems
            before they occur. The re-placement of components in the A-model sounds
            like a partial response to the heat problems, although it must have
            occurred before most of those problems occurred in the straight 751.

            Yes, I have been told that the 761 was basically a 751A with Autotuner
            and power supply all in one cabinet; apparently the 765 was a
            significantly different animal.

            I have seen many references by satisfied customers to Malcolm Technical
            Services. If I have problems in the future I will strongly consider them.

            73
            Pete K5GM

            >________________________________________________________________________
            >
            >1a. Re: IC-751A vs IC-751 (was: distorted audio on 40 only)
            > Posted by: "adb1x1" adb1x1@... adb1x1
            > Date: Sun Sep 10, 2006 7:30 am (PDT)
            >
            >Pete,
            > The 751A does have the same VCO and electrolytics issues (I have
            >the A version as well), but I have noticed that there was some
            >changes in the parts layout on the PLL board and quite a few changes
            >on the main board, so that the electrolytic caps aren't as near the
            >heatsink, so they probably won't go a quickly in the 751A.
            >
            > Though I haven't changed them yet, it looks like the VCO caps are
            >the same type used in the 751. When I first got this one, it needed
            >some alignment. When it came time to adjust these trimmers they were
            >tight and felt a little sticky. I suspect there's a little bee's wax
            >on them, so I'm sure I'll be replacing them soon.
            >
            >Anthony
            >
            >
            >
            >
            >
            >
            >Messages in this topic (4)
            >________________________________________________________________________
            >
            >1c. Re: IC-751A vs IC-751 (was: distorted audio on 40 only)
            > Posted by: "Ray" w8cnl@... w8cnl
            > Date: Sun Sep 10, 2006 10:19 am (PDT)
            >
            >I have been told there are quite a few differences in the 751 and the 751A.
            >Also the 751A was the proto type of the 761. Plus they added the built in
            >UX-14 and AT-150 antenna tuner for example.
            >I have both here now and wouldn't get rid of either (maybe for enough
            >money ).
            >My 761 is completely stock. The 751A has a 250 cycle filter added. Fantastic
            >for CW and RTTY !! I have opened it up for full transmit. The 60 meter band
            >works beautiful in it. My came configured for IF shift. Changed it back to
            >PBT. Yes, PBT is much better. I use both radios to drive a little modified
            >AL-811 amp. Does it perform ?? How does 336/336 sound. Still need BS7H. 291
            >RTTY.
            >
            >Any mods or eminence that I didn't feel comfortable doing has all been
            >perform by Scott Malcom at MTS. VCO mods, etc. His work is perfect and
            >prices very reasonable.
            >
            >Hang on to your 751A. It will give you many years of service.
            >
            >73 and DX to you.
            >
            >
            >
            >Raymond H. McClure - W8CNL
            >5 McKenzie Circle
            >North Augusta, S.C.
            >29841-4319
            >
            >Meddle not in the Affairs of Dragons, for Thou Art Crunchy and Taste Good
            >with Catsup or BBQ Sauce
            >
            >* * * * * * * * * * * * * * * * * * * * * * * *
            >
            >
            >
            >
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