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Another TR7 implosion

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  • Craig Roberts
    I bought an extra TR7 as a backup, just in case... Well, now BOTH of them are out of commission. Grrrr. The latest failure went like this: 1. During a normal
    Message 1 of 18 , Feb 1, 2011
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      I bought an extra TR7 as a backup, just in case...

      Well, now BOTH of them are out of commission. Grrrr.

      The latest failure went like this:

      1. During a normal transmission, the display went haywire. I unkeyed
      the rig and cycled the RCT switch (which had seemed a little flaky
      lately, even though it had been thoroughly cleaned recently).

      2. I keyed the rig again. The output meter pegged. I backed off the
      output to zero and keyed again. The ALC LED lit and the meter pegged
      again (there was no ALC action at all). I detected the unmistakable
      smell of a frying resistor and shut down the rig.

      I have yet to find the charred component, but I haven't had the radio
      apart yet. The smell seems to be centered around the ALC board or final
      amp brick. This radio has been thoroughly serviced twice in the last
      year and appears never to have been abused. (In fact, it looks near new
      inside and out).

      Whaddya think? (My other radio doesn't transmit, either -- but its
      failure seems more like a driver or PIN diode problem).

      I love my TR7s but, I gotta tell ya, this is getting very frustrating.

      73,
      Craig
      W3CRR
    • Jim Shorney
      I ve been pondering this. It almost seems like you have multiple different problems. The display problem suggests intermittent Molex connectors, or perhaps the
      Message 2 of 18 , Feb 1, 2011
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        I've been pondering this. It almost seems like you have multiple different
        problems. The display problem suggests intermittent Molex connectors, or
        perhaps the DC-DC converter power supply or a different power problem of some
        sort. The pegged meter sounds like PA deck oscillation. The burned smell, maybe
        PIN diodes or the aforementioned DC-DC power suppy. All areas to look at.

        In the past, it seems that a lot of strange 7-line problems can be cured by
        pulling all of the PC boards one at a time, cleaning and DeOxiting the Molex
        connectors (check the female connectors for tension too), and re-seating. Also,
        failure of the large filter cap on the DC-DC power supply board can cause
        strange problems. Replace it with a modern 105C temperature rated cap as
        preventative maintenance while you have the rig apart. PA deck oscillation can
        be caused by excessive predriver gain, but this usually only shows up on the 40
        Meter band segment; I've also seen leaky driver transistors cause it. Check
        the base voltage on the driver transistors in RX, it should be 0 volts. If it's
        anything even remotely approaching 0.6, you have leakage. The PA deck can be
        removed as a unit, without disconnecting any wires, and set on top of the radio
        by removing four screws on the right side of the rig. Check the PIN diodes as
        well, there are procedures on wb4hfn.com and the Drakelist web site.

        I hope this helps.

        73

        -Jim


        On Tue, 01 Feb 2011 14:34:29 -0500, Craig Roberts wrote:

        >I bought an extra TR7 as a backup, just in case...
        >
        >Well, now BOTH of them are out of commission. Grrrr.
        >
        >The latest failure went like this:
        >
        >1. During a normal transmission, the display went haywire. I unkeyed
        >the rig and cycled the RCT switch (which had seemed a little flaky
        >lately, even though it had been thoroughly cleaned recently).
        >
        >2. I keyed the rig again. The output meter pegged. I backed off the
        >output to zero and keyed again. The ALC LED lit and the meter pegged
        >again (there was no ALC action at all). I detected the unmistakable
        >smell of a frying resistor and shut down the rig.
        >
        >I have yet to find the charred component, but I haven't had the radio
        >apart yet. The smell seems to be centered around the ALC board or final
        >amp brick. This radio has been thoroughly serviced twice in the last
        >year and appears never to have been abused. (In fact, it looks near new
        >inside and out).
        >
        >Whaddya think? (My other radio doesn't transmit, either -- but its
        >failure seems more like a driver or PIN diode problem).
        >
        >I love my TR7s but, I gotta tell ya, this is getting very frustrating.
        >
        >73,
        >Craig
        >W3CRR
        >
        >
        >


        --
        Ham Radio NU0C
        Lincoln, Nebraska, U.S.S.A.
        TR7/RV7/R7A/L7, TR6/RV6, T4XC/R4C/L4B, NCL2000, SB104A, R390A, GT550A/RV550A, HyGain 3750, IBM PS/2 - all vintage, all the time!

        "Give a man a URL, and he will learn for an hour; teach him to Google, and he will learn for a lifetime."

        HyGain 3750 User's Group - http://groups.yahoo.com/group/HyGain_3750/
        http://incolor.inetnebr.com/jshorney
        http://www.nebraskaghosts.org
      • Dave Drake
        Craig, First question: Do you have a service manual? If you do, even the original version, (there were two), find the traces on the motherboard that are 10v
        Message 3 of 18 , Feb 2, 2011
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          Craig,
          First question: Do you have a service manual?

          If you do, even the original version, (there were two), find the traces on the motherboard that are 10v lines and check to see if the rig has proper voltage. Also then check the other traces for proper voltage in both rx and tx.

          On the PA brick, make sure the predriver is backed off of maximum a bit. If it is at max, then you may have another problem lurking. Yes, pin diodes can be a problem and are very difficult to get to. It would be best to leave that to someone experienced at replaceing them.

          My experience is like Jims, that the very first thing to do when you receive your new/old TR7 is to remove every board and clean contacts. Also clean the molex connectors on all plugs. Once you have done this, you can then reasonably trouble shoot any real problems. However, it all starts from the power supply board. Jim is also correct with the capacitor on the power supply board. The PS7 does not provide very clean DC, and the power supply board finishes the job. Thats the way Drake designed it.

          I would suggest if you do not have a service manual, you try to obtain one to go much further. If you are not inclined to really dig in, then I would suggest you send the rig (s) to a good Drake service man to repair and get up and running. There are several listed on Ron's website (wb4hfn) as well as Ron himself. A couple more over around the Dayton area/SW Ohio. Jeff Covelli up near Clevelend. I will say if you send it to any of these guys they'll stand behind their work and provide phone support to help you out of any further issues.

          Aligned properly, a TR7 is still an excellent ham radio both in receive quality and transmit audio quality. I am continually amazed at how it compares to newer radios such as a TT Omni VII and Icom 7200 (at my location in daily use).

          Good luck,
          David
          Wd9cmd

          [Non-text portions of this message have been removed]
        • Craig Roberts
          Many thanks to Jim and Dave for their suggestions. I have the afternoon off today - a real rarity -- so I will dig into the rig a bit. (I do have a service
          Message 4 of 18 , Feb 2, 2011
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            Many thanks to Jim and Dave for their suggestions. I have the afternoon
            off today - a real rarity -- so I will dig into the rig a bit. (I do
            have a service manual).

            This radio's been repaired by Jeff a couple of times for transmit
            problems; once just before I bought the radio a couple of years ago and
            once about six months ago. The last service included PIN diode
            replacement and a new T/R relay (which, in fact, was the needed
            repair). Jeff's performed his usual beautiful service and I am
            confident that the Molex connectors are clean. Neverthless, I do pull
            and re-seat the boards periodically "just in case."

            I removed the power supply board last night and -- by golly -- I think
            the 220 uf electrolytic is the component that fried. It is not charred,
            but the overheated smell seems to be coming from it. Anyone who's
            experienced burned components knows that the unmistakable odor tends to
            permeate everything around it and is surprisingly hard to pinpoint --
            though resistors that burst into flame are easier to find :-) .

            Anyway, I'll be replacing that cap go from there with voltage
            measurements, etc, as needed.

            This particular TR7 is in such beautiful shape that it's misleading. I
            keep forgetting that's it is over 30 years old and -- naturally -- prone
            to breakdowns from time to time.

            I'll keep y'all posted.

            Thanks again.

            73,

            Craig
            W3CRR
          • Craig Roberts
            Some progress and a new mystery. Replacement of the 22 uf electrolytic on the power supply board indeed fixed the display problem. The radio has awakened from
            Message 5 of 18 , Feb 2, 2011
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              Some progress and a new mystery.

              Replacement of the 22 uf electrolytic on the power supply board indeed
              fixed the display problem. The radio has awakened from the dead and it
              now receives normally. (I did adjust the power supply board voltages).

              However, when the transmitter is keyed into a dummy load now, it acts as
              if it's working into an open circuit. Forward and reflected powers
              indicate identically, there's no ALC indication and no output.

              Hmmmm. Where do I go from here?

              Thanks again,

              Craig
              W3CRR
            • Jim Shorney
              ... Hmmm, that s an odd one. I would check Q307 and Q307, the +10 T and R switch transistors on the TX Exciter board. I m starting to feel like I m the only
              Message 6 of 18 , Feb 2, 2011
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                On Wed, 02 Feb 2011 15:50:20 -0500, Craig Roberts wrote:

                >However, when the transmitter is keyed into a dummy load now, it acts as
                >if it's working into an open circuit. Forward and reflected powers
                >indicate identically, there's no ALC indication and no output.
                >
                >Hmmmm. Where do I go from here?


                Hmmm, that's an odd one. I would check Q307 and Q307, the +10 T and R switch
                transistors on the TX Exciter board.

                I'm starting to feel like I'm the only one on this group.... :)

                73

                -Jim


                --
                Ham Radio NU0C
                Lincoln, Nebraska, U.S.S.A.
                TR7/RV7/R7A/L7, TR6/RV6, T4XC/R4C/L4B, NCL2000, SB104A, R390A, GT550A/RV550A, HyGain 3750, IBM PS/2 - all vintage, all the time!

                "Give a man a URL, and he will learn for an hour; teach him to Google, and he will learn for a lifetime."

                HyGain 3750 User's Group - http://groups.yahoo.com/group/HyGain_3750/
                http://incolor.inetnebr.com/jshorney
                http://www.nebraskaghosts.org
              • Dave Drake
                Just an FYI, don t forget to make sure you have all correct voltages on the mother board, not just 10v trace. Also, if the 10v line was off by very much, say a
                Message 7 of 18 , Feb 3, 2011
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                  Just an FYI, don't forget to make sure you have all correct voltages on the mother board, not just 10v trace.

                  Also, if the 10v line was off by very much, say a few tenths of a volt either way, you may need a full realignment !! The radio is very sensitive (in how well it functions and behaves) to the 10v circuit adjustment.

                  Its critical that voltages on all the motherboard traces are behaving properly in both transmit and receive.

                  If Jeff did work on the rig recently, just give him a call on the land line. I know he'll help you sort it out over the phone if possible.

                  Anyway,.....voltages on the motherboard....start there.

                  David
                  Wd9cmd

                  [Non-text portions of this message have been removed]
                • Craig Roberts
                  Jim -- you were absolutely correct. Q307 and R363 on the Transmitter Exciter Board were fried -- literally - thus killing the T/R switching. It appears as if
                  Message 8 of 18 , Feb 6, 2011
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                    Jim -- you were absolutely correct.

                    Q307 and R363 on the Transmitter Exciter Board were fried -- literally -
                    thus killing the T/R switching. It appears as if the 220 uf electrolytic
                    on the Power Supply Board failed, sending unpleasantness down the +10V
                    line. Replacing the three components mentioned has restored the radio
                    to normal operation (at least for the time being).

                    Thanks very much!

                    73,
                    Craig
                    W3CRR
                  • Jim Shorney
                    I m glad that you got it going, Craig! I ll say it again, for anyone within reading distance, replace that 220 uF cap as preventative maintenance! That is
                    Message 9 of 18 , Feb 6, 2011
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                      I'm glad that you got it going, Craig!

                      I'll say it again, for anyone within reading distance, replace that 220 uF cap
                      as preventative maintenance! That is probably the one cap in the radio that is
                      under the most stress, strange and bad things can happen when it fails (or even
                      begins to fail). These caps are 30 years old now, it's time.

                      73

                      -Jim

                      On Sun, 06 Feb 2011 17:56:52 -0500, Craig Roberts wrote:

                      >Jim -- you were absolutely correct.
                      >
                      >Q307 and R363 on the Transmitter Exciter Board were fried -- literally -
                      >thus killing the T/R switching. It appears as if the 220 uf electrolytic
                      >on the Power Supply Board failed, sending unpleasantness down the +10V
                      >line. Replacing the three components mentioned has restored the radio
                      >to normal operation (at least for the time being).
                      >
                      >Thanks very much!
                      >
                      >73,
                      >Craig
                      >W3CRR
                      >
                      >
                      >
                      >
                      >


                      --
                      Ham Radio NU0C
                      Lincoln, Nebraska, U.S.S.A.
                      TR7/RV7/R7A/L7, TR6/RV6, T4XC/R4C/L4B, NCL2000, SB104A, R390A, GT550A/RV550A, HyGain 3750, IBM PS/2 - all vintage, all the time!

                      "Give a man a URL, and he will learn for an hour; teach him to Google, and he will learn for a lifetime."

                      HyGain 3750 User's Group - http://groups.yahoo.com/group/HyGain_3750/
                      http://incolor.inetnebr.com/jshorney
                      http://www.nebraskaghosts.org
                    • Craig Roberts
                      Heed Jim s advice. That cap was one of those little things I was going to get to but , somehow, never did. I just feel very lucky the damage its failure
                      Message 10 of 18 , Feb 6, 2011
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                        Heed Jim's advice. That cap was one of those little things I was "going
                        to get to" but , somehow, never did. I just feel very lucky the damage
                        its failure caused wasn't worse.

                        73,

                        Craig
                        W3CRR

                        On 2/6/2011 6:42 PM, Jim Shorney wrote:
                        >
                        > I'm glad that you got it going, Craig!
                        >
                        > I'll say it again, for anyone within reading distance, replace that
                        > 220 uF cap
                        > as preventative maintenance! That is probably the one cap in the radio
                        > that is
                        > under the most stress, strange and bad things can happen when it fails
                        > (or even
                        > begins to fail). These caps are 30 years old now, it's time.
                        >
                        > 73
                        >
                        > -Jim
                        >
                        > On Sun, 06 Feb 2011 17:56:52 -0500, Craig Roberts wrote:
                        >
                        > >Jim -- you were absolutely correct.
                        > >
                        > >Q307 and R363 on the Transmitter Exciter Board were fried -- literally -
                        > >thus killing the T/R switching. It appears as if the 220 uf electrolytic
                        > >on the Power Supply Board failed, sending unpleasantness down the +10V
                        > >line. Replacing the three components mentioned has restored the radio
                        > >to normal operation (at least for the time being).
                        > >
                        > >Thanks very much!
                        > >
                        > >73,
                        > >Craig
                        > >W3CRR
                        > >
                        > >
                        > >
                        > >
                        > >
                        >
                        > --
                        > Ham Radio NU0C
                        > Lincoln, Nebraska, U.S.S.A.
                        > TR7/RV7/R7A/L7, TR6/RV6, T4XC/R4C/L4B, NCL2000, SB104A, R390A,
                        > GT550A/RV550A, HyGain 3750, IBM PS/2 - all vintage, all the time!
                        >
                        > "Give a man a URL, and he will learn for an hour; teach him to Google,
                        > and he will learn for a lifetime."
                        >
                        > HyGain 3750 User's Group - http://groups.yahoo.com/group/HyGain_3750/
                        > http://incolor.inetnebr.com/jshorney
                        > http://www.nebraskaghosts.org
                        >
                        >



                        [Non-text portions of this message have been removed]
                      • Craig Roberts
                        Shucks! I thought I had it. After replacing the 220 uf electrolytic on the power supply board and a fried switching transistor and associated components on
                        Message 11 of 18 , Feb 8, 2011
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                          Shucks! I thought I had it.

                          After replacing the 220 uf electrolytic on the power supply board and a
                          fried switching transistor and associated components on the Transmit
                          Exciter board late yesterday, all seemed well. Receive and transmit
                          were normal in all modes and a simple tweaking of the carrier null and
                          power supply board voltage put everything in order quickly. The radio
                          acted just fine for a couple of hours.

                          Then -- after several faultless CW QSOs on 40 meters, I switched modes
                          to SSB. The radio wouldn't transmit (even though SSB had worked fine
                          earlier in the evening). On receive, the display jumped to the dreaded
                          17.000 MHz range, squirreled around a bit and finally settled on 17.650
                          or so with the receiver dead. Keying the radio on CW returned it to
                          normal transmit operation in the 7 MHz band in that mode, but releasing
                          the key continued to result in an incorrect, out-of-band display and a
                          dead receiver.

                          Apparently, the T/R transistors(s) on the transmit exciter board are
                          gone again -- but freezing the rig in the transmit mode this time.

                          I am completely at a loss here. I fear it's time to break out the
                          bubble wrap (again).
                        • Garey Barrell
                          Craig - The 17 MHz output just means the low band PLL is unlocked. When you were working on the radio did you happen to measure the +24V bus? Unlocked PLLs
                          Message 12 of 18 , Feb 8, 2011
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                            Craig -

                            The 17 MHz output just means the low band PLL is unlocked.

                            When you were working on the radio did you happen to measure the +24V
                            bus? Unlocked PLLs that 'sometimes' lock are often an indication of low
                            +24 V. If you switch to 20M or above does the frequency lock, or does
                            it wander up to about 32 MHz?

                            The transistor 'fuses' on the Transmit Exciter board are just that.
                            Totally unprotected and even a momentary short or overload on the 10R or
                            10T bus will kill one.

                            73, Garey - K4OAH
                            Glen Allen, VA

                            Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
                            and TR-4/C Service Supplement CDs
                            <www.k4oah.com>


                            Craig Roberts wrote:
                            > Shucks! I thought I had it.
                            >
                            > After replacing the 220 uf electrolytic on the power supply board and a
                            > fried switching transistor and associated components on the Transmit
                            > Exciter board late yesterday, all seemed well. Receive and transmit
                            > were normal in all modes and a simple tweaking of the carrier null and
                            > power supply board voltage put everything in order quickly. The radio
                            > acted just fine for a couple of hours.
                            >
                            > Then -- after several faultless CW QSOs on 40 meters, I switched modes
                            > to SSB. The radio wouldn't transmit (even though SSB had worked fine
                            > earlier in the evening). On receive, the display jumped to the dreaded
                            > 17.000 MHz range, squirreled around a bit and finally settled on 17.650
                            > or so with the receiver dead. Keying the radio on CW returned it to
                            > normal transmit operation in the 7 MHz band in that mode, but releasing
                            > the key continued to result in an incorrect, out-of-band display and a
                            > dead receiver.
                            >
                            > Apparently, the T/R transistors(s) on the transmit exciter board are
                            > gone again -- but freezing the rig in the transmit mode this time.
                            >
                            > I am completely at a loss here. I fear it's time to break out the
                            > bubble wrap (again).
                            >
                            >
                            >
                          • Craig Roberts
                            Garey Barrell wrote: If you switch to 20M or above does the frequency lock, or does it wander up to about 32 MHz? Yup -- it does wander up to 32 MHz or
                            Message 13 of 18 , Feb 8, 2011
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                              Garey Barrell wrote:"If you switch to 20M or above does the frequency
                              lock, or does
                              it wander up to about 32 MHz?"

                              Yup -- it does wander up to 32 MHz or thereabouts on the higher bands.

                              Convinced my problem stemmed from the 220 uf electrolytic and the 10 V
                              line alone, I did NOT check the 24 volt line (foolish me). It could be,
                              I suppose, that another problem has befallen the power supply board.

                              I'll let you know.

                              Thanks very much, Garey.

                              73,

                              Craig
                              W3CRR

                              ,
                              >
                              >
                              > The 17 MHz output just means the low band PLL is unlocked.
                              >
                              > When you were working on the radio did you happen to measure the +24V
                              > bus? Unlocked PLLs that 'sometimes' lock are often an indication of low
                              > +24 V.
                              >
                              > The transistor 'fuses' on the Transmit Exciter board are just that.
                              > Totally unprotected and even a momentary short or overload on the 10R or
                              > 10T bus will kill one.
                              >
                              > 73, Garey - K4OAH
                              > Glen Allen, VA
                              >
                              > Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
                              > and TR-4/C Service Supplement CDs
                              > <www.k4oah.com>
                              >
                              > Craig Roberts wrote:
                              > > Shucks! I thought I had it.
                              > >
                              > > After replacing the 220 uf electrolytic on the power supply board and a
                              > > fried switching transistor and associated components on the Transmit
                              > > Exciter board late yesterday, all seemed well. Receive and transmit
                              > > were normal in all modes and a simple tweaking of the carrier null and
                              > > power supply board voltage put everything in order quickly. The radio
                              > > acted just fine for a couple of hours.
                              > >
                              > > Then -- after several faultless CW QSOs on 40 meters, I switched modes
                              > > to SSB. The radio wouldn't transmit (even though SSB had worked fine
                              > > earlier in the evening). On receive, the display jumped to the dreaded
                              > > 17.000 MHz range, squirreled around a bit and finally settled on 17.650
                              > > or so with the receiver dead. Keying the radio on CW returned it to
                              > > normal transmit operation in the 7 MHz band in that mode, but releasing
                              > > the key continued to result in an incorrect, out-of-band display and a
                              > > dead receiver.
                              > >
                              > > Apparently, the T/R transistors(s) on the transmit exciter board are
                              > > gone again -- but freezing the rig in the transmit mode this time.
                              > >
                              > > I am completely at a loss here. I fear it's time to break out the
                              > > bubble wrap (again).
                              > >
                              > >
                              > >
                              >
                              >



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