In a message dated 09/02/2008, lconklin@............ writes:

I have  put a lot of effort into trying to figure out what is going on, to no 
 avail.  In one of the previous episodes, I disconnected the power to the  
oscillator that drives the antenna plate, and opened the loop for the feedback  
damping.  There was no significant change in the output, which led me at  the 
time to conclude that there must either be something wrong with the  
electronics board, or some sort of electrical/magnetic pick-up.    Despite a lot of  
diddling around, I couldn't determine a cause, and  eventually, the system 
settled down without my having done anything specific  to fixing it.  And, 
neither theory fits well with this current  episode, which started when I 
mechanically disurbed the sensor a little by  adjusting the leveling.

I threw together a web page that shows  the onset of the problem, as well as 
short time intervals  before and  after the problem started this time.  If 
anyone cares to take a look at  it and offer their thoughts (or condolences), I'd 
like to hear  them.



Hi Larry,
 
    The problem seems to be with the first opamp or  it's circuit.
 
    Clean the input connectors with fine wire wool and  coat them with 
vaseline.
    If the resistors are NOT metal film, check them for  damage / the correct 
resistance, maybe replace the input circuit ones with metal  film resistors. 
This could simply be a faulty resistor. 
    Visually inspect the solder joints with a  magnifying glass for any which 
appear faulty.
    You can get a solder fault called crevice  corrosion, when corrosion 
creeps in between the copper board and the solder  joints. Remove one solder blob 
on say a resistor and then scratch the tinned  area with a knife. If you have 
crevice corrosion, the solder will peel off  leaving a dark brown oxide film 
on the copper strip.
    It could also be that the opamp is faulty.  Does it unplug, or is it 
soldered in? Can you replace it easily?
 
    You can buy a spray can of freezing fluid. You  monitor the signal output 
and then spray freeze the components in turn. If one  is faulty, you are 
likely to see a large change in the output signal.
    If the board gets damp while in use, you can brush  coat it with single 
pack polyurethane varnish for protection.
 
    Regards,
 
    Chris Chapman



   






In a message dated 09/02/2008, lconklin@............ writes:
<=
FONT=20
  style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#000000 size=
=3D2>I have=20
  put a lot of effort into trying to figure out what is going on, to no=20
  avail.  In one of the previous episodes, I disconnected the power to=20=
the=20
  oscillator that drives the antenna plate, and opened the loop for the feed=
back=20
  damping.  There was no significant change in the output, which led me=
 at=20
  the time to conclude that there must either be something wrong with the=20
  electronics board, or some sort of electrical/magnetic pick-up.  =
;=20
  Despite a lot of  diddling around, I couldn't determine a cause, and=20
  eventually, the system settled down without my having done anything specif=
ic=20
  to fixing it.  And, 
neither theory fits well with this current=20
  episode, which started when I mechanically disurbed the sensor a little by=
=20
  adjusting the leveling.

  I threw together a web page that sho=
ws=20
  the onset of the problem, as well as short time intervals  before and=
=20
  after the problem started this time.  If anyone cares to take a look=20=
at=20
  it and offer their thoughts (or condolences), I'd like to hear=20
them.


Hi Larry,
 
    The problem seems to be with the first opamp or=
=20
it's circuit.
 
    Clean the input connectors with fine wire wool=20=
and=20
coat them with vaseline.
    If the resistors are NOT metal film, check them=
 for=20
damage / the correct resistance, maybe replace the input circuit ones with m=
etal=20
film resistors. This could simply be a faulty resistor. 
    Visually inspect the solder joints with a=20
magnifying glass for any which appear faulty.
    You can get a solder fault called crevice=20
corrosion, when corrosion creeps in between the copper board and the so=
lder=20
joints. Remove one solder blob on say a resistor and then scratch the tinned=
=20
area with a knife. If you have crevice corrosion, the solder will peel off=20
leaving a dark brown oxide film on the copper strip.
    It could also be that the opamp is faulty.=
=20
Does it unplug, or is it soldered in? Can you replace it easily?
 
    You can buy a spray can of freezing fluid. You=20
monitor the signal output and then spray freeze the components in turn. If o=
ne=20
is faulty, you are likely to see a large change in the output signal.
    If the board gets damp while in use, you can br=
ush=20
coat it with single pack polyurethane varnish for protection.
 
    Regards,
 
    Chris Chapman