The first thing to do when faced with polarity questions is get out the
schematic of the rig. See where the plus side of electrolytic caps is
connected re the power socket. IF the negative of each electrolytic
goes to the same point electrically, (continuity) with the shield side
of the Coax or antenna connector, and the outer shield of a coax power
connector, then you know the center pin is positive voltage.
The exceptions to this electrolytic aid, is those caps that couple stage
to stage, or in the audio or speaker line.
Usually you can see which side of the power connector has 0 ohms to the
chassis box, or the ground plane of the circuit board, and go from there.
If the circuit does not already have it, add an in line fuse to the
power connector, and from that fuse to the board run a 1 amp silicon
diode from the positive side connection to the circuit ground. Then, if
you or someone connects the wrong polarity to the back panel, you blow
the fuse, and can correct the error without damage to board components.
You may NOT have blown anything, there may be an internal fuse already
blown, or other problem.
Good Luck,
73,
Stuart Rohre
K5KVH
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