Mike
I would be very surprised if your MkV was exhibiting an emi problem that
hasn't been observed on other MkVs.
The NB button is a simple 'make' switch. The led and the NB switch
action are electrically separate: the switch action is needed to turn on
the NB circuitry and other stuff that beeps and feeds back a signal to
turn on the led.
Thoughts:
It could be a stressed connection from the SW-C board - except that on
one side the NB switch shares a decoded connection with the TUNER
switch, so this would be intermittent too. Similarly, if it was a
connector problem on the other side of the NB switch then all three
filter buttons would be intermittent.
I would put my money on this being a mechanical problem with the NB
switch assembly. Maybe a very small bit of something rolling around
inside the switch that blocks the contacts in the 'right' position or
something that has lost spring loading that is aided by gravity in the
wrong position.
Good luck!
Pete, G4PLZ
Mike and Alicia Fanning wrote:
> I am having a really bizarre problem with my recently purchased used Mark V
> Field. When I bought the rig, the noise blanker button was intermittent -
> that is, you had to hit it several times to engage or disengage the noise
> blanker (no beep and no LED toggle). I just bought the roofing filter mod
> and some CW filters from Inrad, and while I was installing the mod, I
> decided to fold down the front panel and see if there was anything obviously
> wrong with the PC board assembly that houses the NB button. I checked
> continuity on the button, and electrically everything seems fine. I then
> powered up the radio (with the front panel still loose), and as I am folding
> in the front panel to screw it back into place, the NB button works perfect
> until just before the panel reaches vertical. If I tilt the front panel
> just a few degrees outward, all is well again. I have tried this same
> experiment with no power applied and a multimeter checking the continuity of
> the NB button while holding down the button, and the switch always seems to
> make good closure, no matter what the position of the front panel assembly.
> However, when I power it back up, same story as before - just before you get
> the panel vertical, the NB button quits working. I unscrewed the two
> "hinge" screws at the base of the front panel assembly, kept the front panel
> vertical, and moved it slightly backward and forward (closer and farther to
> the chassis). Again, the NB button quit working when I got within close
> proximity of the chassis.
>
> There is a pc board of some variety with a metal can around it that resides
> right behind the NB and filter selection buttons, approximately 3-4 inches
> tall and about an inch wide. I am guessing this is the shield for the high
> voltage power supply that runs the front panel display. My current theory
> is EMI getting into a control line and corrupting the pushbutton data, but
> at this point, I am out of airspeed, altitude, and ideas.
>
> Has anyone else seen this behavior? Can anyone offer some helpful tips?
>
> Still scratching my head,
> Mike, K4GU
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