Heath Product Notice

[Dave Wood]

Heathites listen up!  Like many hams I have on my workbench a Heath IM-103
line voltage monitor.  Really quite a neat gadget.  But beware! This unit
has a built in engineering fault I found out about last night about 2am.  I
had noted that in the past two days the readings were erratic.  Thinking the
unit was getting ready to roll over (understatement) I put it in line with
about 14 other projects to get attention on the bench.  Well as Ricky
Ricardo says, "it splained it to me last nite".  I was awoken by a loud
hissing sound accompanied by the groaning of my 15 amp breaker in the main
panel.  Then silence!  About one minute later, the smoke alarms in the shack
went off.  Needless to say, I'm up now!  Ran into the shack to find the room
thick with smoke all coming from the IM-103.  Quickly tried to unplug the
unit in the dark, (breaker tripped) only to burn by hand with the IM-103, as
it was quite hot.  Spent the next two hours airing out the house!
Evidently, the 16 volt zener reference shorted and after a time it took out
the 10K biasing resistor.  This placed 125VAC across the poor 100 ohm
current limiting resistor in series with the 1/2 wave rectifier.  The
rectifier went, putting raw AC on the filter cap.  Get the picture! Anyway
the moral of the story is Heath did not include a fuse for this little
critter!  If you have one of these I advise putting one in the unit for
protection against catastrophic failure.  Luckly, the unit was mounted away
from any flamable materials or I may have had a real fire.  There is room on
the terminal strip inside the unit for a fuse holder and fuse. 73  and check
these BA's for proper fuse protection.  Dave

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