In message , Jack Twilley
writes
"Mike" == M J Powell writes:

Jack I accidentally reversed the polarity of my DC power supply. I
Jack blew the fuse in my TNC, but I can't find a fuse in my TR-7400A
Jack and the only fuse I see in my TS-520 appears to be for the AC
Jack power supply.

Jack What sort of damage could these radios have suffered?

Mike You may have blown the 'idiot diode' as well as the fuse..

I have the schematic to the TS-520, so I can look for an obvious diode
near the power connector but I don't have the schematic for the
TR-7400A. If anyone out there has the schematic and knows where this
idiot diode is, let me know.

If you have an ohmmeter you could clip it across the DC input pins and
start unsoldering various connections etc.

By the way - have you measured ohms across the DC input? Clip leads both
ways round?

Mike
--
M.J.Powell