[TowerTalk] OR2800 Reed Switch

[Jeffrey Okamitsu]

I know that the reed switch in the OR2800 can fail due to EMP from close by 
lightning strikes.  I have also read where people report intermittent issues 
with the reed switch.

I also seem to have an intermittent problem with the reed switch in my 
OR2800DC.  However, my problem seems to track with temperature, indicating to me 
that it may not be the switch itself but potentially a flakey connection or an 
intermittent short either in the rotor itself or at the cable splice (I have the 
older version with the round connector on the pigtail and not the breakout box).

In my case, when the ambient temperature is low (below about 45F), everything is 
fine and the rotor works exactly as expected - no problems tracking rotation, 
pointing accuracy issues, or position repeatability issues.  However, once the 
temperature goes above about 50 F, the switch reads closed all the time.  I have 
verified that it is closing at the higher temperature as during the last 
episode, when I went QRT the switch was open - two hours later when I went back 
on the air it was closed and would not toggle when I attempted to turn the 
rotor.  Also, when I force the rotor to turn in the RT21 debug mode, I see 
NO change in contact resistance, which means that if the reed is shorted, it's 
REALLY welded.

Then, the next morning when it's cold again, the switch is open and the rotor 
works normally.  I have seen this happen consistently for the last two weeks.

I suspect that this is NOT the reed itself, but potentially one of 
the following:

1) Internal short on the leads to the switch, possibly due to insulation 
failure on wires that are wire tied to torque plate from years of temperature 
cycling.
2) Internal short at the splice going into round connector on pigtail.
3) Clearance between the head of the switch and the gear that contains the 
activating magnet.  As the temperature rises the clearance may get smaller 
leading to permanent activation of the switch.  I think this is very 
unlikely unless the fastener that is holding the switch to the torque plate has 
come loose.  As well, I would expect at least SOME fluctuation in resistance as 
the magnet moves.

Question: Has anyone else encountered the above symptoms (intermittent 
failure that tracks temperature).  If so, what was the actual root cause in your 
case?

73, Jeff
W3KL
 Jeffrey K. Okamitsu, PhD, MBA
+1-609-638-5402 (Mobile)