[Premium-Rx] Racal RA6778C - Product Safety Advisory (Oh MY!!!)

[Ben Dover]

Greetings, Group.

I had a rather odd incident occur this week that I think I
should pass along to other owners of this rig. It COULD 
possibly be an operator safety or fire hazard issue.

I was taking the rig out of it's usual shack location to haul
it on a trip to visit another Premium Receiver fan. While it
was sitting on the floor, I decided I wanted to check what I
had programmed into the memories, and plugged it back in.

When I flipped the AC power switch, the shack's receiver
isolation transformer gave an alarming grunt from overloading,
and I saw the Premium Receiver Nut's Worst Nightmare; a BIG
puff of smoke rolled out of the back of the radio, and the 
isolation transformer's breaker tripped.

Quick investigation showed the radio's fuse to be OK, and the
proper rating. An ohmmeter across the plug showed open in both
AC switch positions.

Pop the dust covers and dig in deeper... The AC power switch is
DPDT, and it showed a DEAD SHORT across the AC line in both
positions!

Grabbed a screwdriver to pull the rear panel & allow removal of 
the power supply module, and there was the source of the smoke;
on each lead of the incoming AC line there are ferrite RF chokes
and bypass capacitors. The plastic heat shrink tubing of one of
the chokes was melted. Removing the choke & doing an ohmmeter
check showed it was open; the choke had done a splendid job of
sacrificing itself to protect the fuse!  ;o)

Quick, temporary repair was a simple matter; strip off the burned
winding, clean the ferrite core, and put on a new winding... but
the AC switch, the source of the problem, is a different matter.


I've long been of the opinion that the RA6778C is a receiver that
is designed to be turned on and LEFT on 24/7 for weeks or months 
at a time. The AC switch is an oddball unit, made to fit the small 
space available on the front panel. It is QUITE flimsy; essentially 
a Rat Shack type mini toggle switch fitted with a large switch's 
mounting bushing and bat handle.

As hams and SWLs we use the radio differently than the original
owners; we turn them on and off a LOT, while the original users 
might power them down once every 6 months or so. The switch is
good enough for occasional useage, but daily? NO WAY!

Dissecting the switch it looks like the internal sliding contact 
somehow rotated 90 degrees and wound up shorting out the AC line.

For the moment, the switch leads have been soldered together and
covered with heat shrink tubing, and the rig is running fine.
However, finding a more robust switch that will fit into the space
provided is going to be a challenge. In the meantime until a
solution to the problem shows up the receiver AC power is being
controlled by the switch on an AC outlet strip.

Just thought I should pass this one along.


73's,

Tom, W9LBB