[AMRadio] Meter help


John Lawson jpl15 at panix.com
Thu Sep 14 11:56:31 EDT 2006



On Thu, 14 Sep 2006, Rick Brashear wrote:

> It seems a while back there was a thread dealing with the repair of panel 
> meters.  Well, I have one that is in need.  It's a Triplett Model 331, 0 - 
> 150 VAC.  It sticks when I turn the face down slightly.  Other than that it 
> works beautifully.  When vertical all is well and when the face is leaned 
> toward the back it works fine.  I've cleaned it as well as I dare by blowing 
> it out gently. Needless to say, something is hanging or binding or something. 
> Any ideas?


    I assume you've got it apart.  If not, there will be a Short Pause 
whilst you disassemble the case and extract the movement and scale plate.


.........


   Okay, we're back!


  There are a couple of places for this kind of stiction to happen.  The 
first would be to carefully inspect, with perhaps a bright point-source of 
light and a magnifier (a jeweler's loupe is excellent for this...), the 
gap between the pole-pieces of the magnet structure and the armature of 
the meter (to which the pointer is attached).  It's entirely possible that 
a tiny sliver of Something Ferrous has gotten in there.  It's doubtful 
that just careful blowing will dislodge magnetic particles like that - 
you'll have to do precision surgery.

   It is possible that, due to shock, the pointer is dragging on the scale 
plate.

  Also - check that the torsion springs are not collapsed, they should look 
like a watch spring.

  Then there is the mechanical zero adjustment - if the case is assembled 
incorrectly, the tiny dog on the adjustment screw can actually bend the 
slotted lever back enough to hang up the pointer system.

   Finally, in many meters the movement is carried in jewels like a watch, 
check to see if those are tight but not binding.


   I rather suspect that you've got Magneto-gunk in the gap, tho....



Cheers

John KB6SCO

PS: if the meter is junk, do not despair, I have three or four exact 
replacements.  Someplace, in a box, under a box, behind some junk, in one 
of my storage space.  I swear, it was *just* here a minnit ago.....   ;)










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