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Author Topic: Re-attach meter inside MFJ-969 Tuner  (Read 4854 times)
NS8Q
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Posts: 135




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« on: July 19, 2013, 06:53:57 PM »

Does anyone have an idea of how I can re-attach the meter inside the mfj-969 tuner?  I discovered that it was pushed inside the case.  I'm not entirely sure how that happened, but when I opened it up, there was a loose screw on the bottom and a white plastic piece that had split.  I'm open to try anything short of buying a new tuner.

73
Chris, NS8Q
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KB4QAA
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« Reply #1 on: July 19, 2013, 08:14:11 PM »

Hot glue?  Dab of epoxy?
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K8AXW
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« Reply #2 on: July 19, 2013, 08:19:12 PM »

I find myself using my hot glue gun more and more!
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W6EM
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« Reply #3 on: July 19, 2013, 09:00:47 PM »

I've found that hot glue doesn't stick to plastic surfaces all that well.  Two-part epoxy would be better, if you could use something like masking tape or electrical tape to hold the meter back against the front panel while the epoxy cures.
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WB6BYU
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« Reply #4 on: July 19, 2013, 09:41:47 PM »

Double stick foam tape solves a lot of mounting issues inside equipment!  I think there is a
meter in side one of my MFJ tuners secured that way (possibly even from the factory?)
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KE3WD
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« Reply #5 on: July 20, 2013, 06:09:06 AM »

I've found that hot glue doesn't stick to plastic surfaces all that well.  

I have found that surfaces that are shiny composites often need roughed up first to give some "tooth" to them and then a good quality hot glue works just fine.  

That roughing an be done with a rough sandpaper, or an Xacto type knife making a few surface cuts in an X pattern, just in the area where you want to apply the hot glue.  

"Good quality hot glue" -  I have also found that there are differences in formulation of this stuff, as well.  For example, there are low heat hot glue sticks designed for low level "pasting" that don't work very well in the electronics repair scenario.  But there are also pro grade sticks with typically higher melting points, harder composition when set, that work very well indeed.  

Silicon RTV can work very well for something like remounting a cracked or broken meter hold-down, too.  Care should be taken to find and use an RTV that does not contain Acetic Acid, which can interact with solder joints in electronics.  These exist and state same on the packaging.  Rule of thumb, if the RTV smells like vinegar when opened, do not use it around electronics. 

73
« Last Edit: July 20, 2013, 06:11:21 AM by KE3WD » Logged
W6EM
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« Reply #6 on: July 20, 2013, 08:01:11 AM »

I've found that hot glue doesn't stick to plastic surfaces all that well.  
...Care should be taken to find and use an RTV that does not contain Acetic Acid, which can interact with solder joints in electronics.  These exist and state same on the packaging.  Rule of thumb, if the RTV smells like vinegar when opened, do not use it around electronics. 
  Thanks for the tip.  I thought all of them used an acetic acid cure.  Reminds me of 40 years ago when the two-way shop I worked for used it to seal roof-mounted halo-loop tuning boxes.  No wonder they had so much trouble with corrosion.  They might have been sealed effectively for water ingress, but I guess condensation and the acid gas did its damage.  Looks like GE cast off not only Jack Welch (who rose from its plastics division) but the RTV acetic acid as well.  One of the reasons I use coax-seal guey polymer to keep water out instead of RTV.

Two part epoxy is fast and cheap.  Double-sided tape gets old and sometimes lets go.  I had some old Heath stuff that I had a problem with that used it.  Fuzzy on the exact recall, though.
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K8AXW
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« Reply #7 on: July 20, 2013, 08:07:53 AM »

Quote
"Good quality hot glue" -  I have also found that there are differences in formulation of this stuff, as well.  For example, there are low heat hot glue sticks designed for low level "pasting" that don't work very well in the electronics repair scenario.  But there are also pro grade sticks with typically higher melting points, harder composition when set, that work very well indeed

I've apparently been using the "right stuff."  I have NEVER had a hot glue failure.  I use it most of the time to anchor LEDs into a panel.  Saves a lot of grief, loose LEDs and if need be, can be unmounted with a little effort.
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WX7G
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« Reply #8 on: July 20, 2013, 09:08:18 AM »

I've had the meters come loose on several MFJ tuners and secured them with silicon caulk.
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NS8Q
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Posts: 135




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« Reply #9 on: July 20, 2013, 09:29:19 PM »

Well I took the past piece that broke off inside and took off the piece that split.  Then I tried my best to reattach it with duct tape inside.  It held, but now the meter doesn't show the full power out.  In fact, it only reads 10 watts out when I know I'm running 100.  I wonder if something else happened when the meter broke loose.
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