DRAKE-RADIO@groups.io

#77224

Hello All,

   You may remember my TR7 that loses lock.  But only when it's in the right mood.  Tap on the big tuning knob and *poof* - no lock.  Hit the "FIX" button a couple times, and lock comes back.

  I had traced it down to the output of the PTO.  Tap the big tuning knob, the output of the PTO goes down to 1/10th of what it should be.

  I even traced it down to the low pass filter at the output of the PTO. When the fault occurred, the voltage at the output was low, and the AC voltage at the buffer transistor was HIGH.  So it pretty much had to be one of those three parts, or their connections.

   I resoldered all the connections, including the feedthrough at the ceramic front plate, and the problem went away.  Yay!  I put the radio back together and used it...for a while...until the problem came back :(.

  So now, I have the TR7 back on the bench.  Flipped down the front panel, popped
the can off the PTO - ready to fix it once & for all.

  Only thing is, it's not doing it now.  Damn I hate that.  I just know it will misbehave if I just put it back together.  Maybe I should just replace the whole
LPF?

  I do have a second PTO;  might just swap them.  Only thing is - that second PTO doesn't have its gear train together.  Somebody ( not me! ) had tried to clean the frequency display disks with some sort of powerful solvent and they'd gone all blotchy-milky.  And it doesn't come off.

  So I would have to move the gear train from the intermittant PTO to the other one.  Is that a big deal?

  One complication - my good HP frequency counter has died.  Blows its fuse.  So I would have to set up this thing without a counter.  Or set the TR7 - all apart - aside, and troubleshoot the counter.  I'd really rather not do that.  I don't like having stuff laying around all apart.

  OK - I swapped PTO's.  Had to do a little mix & match.  Put it all together, it works.  HOWEVER - the gear train is not working correctly.  Both indicator wheels
are turning in unison, and the frequency change is way too swift. Something need lubrication?

                     - Jerry, KF6VB

#77225

Jerry,
I had the same problem (PTO output dropping) in my T-4XB when I bought it.
It turned out to be the ground connection was via a lug under the PTO mounting stud.? Probably was loose from the factory.
I finally found it by poking around.? I poked it enough that the buffer transistor inside failed, I figured the PTO had found ground through that transistor
somehow.
Maybe your problem?
73,
Gary
WB6OGD

#77226

I have a TR7 PTO, total;y disassembled where it could be, ultrasonic cleaned to remove old lubricant, relayed and reassembled. This one its as good as factory new. $50 shipped in CONUSA.

Gary 

W0DVN

Show quoted text

On Apr 14, 2024, at 3:02?PM, jerry-KF6VB <jerry@...> wrote:

Hello All,

  You may remember my TR7 that loses lock.  But only when it's in the right mood.  Tap on the big tuning knob and *poof* - no lock.  Hit the "FIX" button a couple times, and lock comes back.

 I had traced it down to the output of the PTO.  Tap the big tuning knob, the output of the PTO goes down to 1/10th of what it should be.

 I even traced it down to the low pass filter at the output of the PTO.  When the fault occurred, the voltage at the output was low, and the AC voltage at the buffer transistor was HIGH.  So it pretty much had to be one of those three parts, or their connections.

  I resoldered all the connections, including the feedthrough at the ceramic front plate, and the problem went away.  Yay!  I put the radio back together and used it...for a while...until the problem came back :(.

 So now, I have the TR7 back on the bench.  Flipped down the front panel, popped
the can off the PTO - ready to fix it once & for all.

 Only thing is, it's not doing it now.  Damn I hate that.  I just know it will misbehave if I just put it back together.  Maybe I should just replace the whole
LPF?

 I do have a second PTO;  might just swap them.  Only thing is - that second PTO doesn't have its gear train together.  Somebody ( not me! ) had tried to clean the frequency display disks with some sort of powerful solvent and they'd gone all blotchy-milky.  And it doesn't come off.

 So I would have to move the gear train from the intermittant PTO to the other one.  Is that a big deal?

 One complication - my good HP frequency counter has died.  Blows its fuse.  So I would have to set up this thing without a counter.  Or set the TR7 - all apart - aside, and troubleshoot the counter.  I'd really rather not do that.  I don't like having stuff laying around all apart.

 OK - I swapped PTO's.  Had to do a little mix & match.  Put it all together, it works.  HOWEVER - the gear train is not working correctly.  Both indicator wheels
are turning in unison, and the frequency change is way too swift. Something need lubrication?

                    - Jerry, KF6VB

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TR7 PTO