[R-390] Troubleshooting "unrepairable" radios

[Tom Norris]

Jon's solution reminded me of a Troubleshooting Adventure I had no  
too long ago on a radio marked "not repairable"

This was a 1962 Amelco that appeared all-original. Seems every time  
you'd turn it on, it would blow the RF/IF B+ fuse.  First thing I  
found was that line showed a short, and indeed there was a pinched  
wire right at the BFO switch.  I turned off the radio, unplugged the  
radio, took off the front panel, fixed the wire and the short went  
away. Put it all back together.  *bam* the fuse blows again when it's  
switched on.  I unplug the radio and check that side of B+ at the  
fuse, and sure enough, a dead short to ground.  I unplug the IF, RF,  
Crystal Osc, still, dead short.  Unplug Audio and PTO.  Power  
Supply.  Dead short.  I remove the front panel and I check around,  
nothing unusual -- and no short any longer.  I plug in all the  
modules, switch off the power, plug in the radio, and with the front  
panel down turn it on.  Radio works fine.  Mumble "bad wiring  
harness..." unplug, turn off, button up.  Plug in turn on.... and as  
I turn it on I just *happen* to be looking down the front panel and  
see a *flash* as my next to last fuse in the box blows.

Defect Found: Terminals from the function switch were *just* touching  
the RF deck.  Apparently this particular switch stuck back behind the  
panel enough to allow this.  Nothing appeared to be modified in any  
way nor did switch appear to be damaged.

Solution: Bent terminals out of the way and removed lockwasher  
between switch bushing and panel.  Considered replacing function  
switch in the future.

73, Merry Christmas and happy troubleshooting.

Tom NU4G



On Dec 14, 2005, at 3:58 PM, Jon wrote:
> ... It was a pinched wire (BFO wire) ...