[R-390] R390 troubleshooting - I'm stuck, 3/8A fuse pops

[Tisha Hayes]

I would put money on it that there is a capacitor somewhere that is the
problem. While it may not test as a dead short it is probably leaking like
crazy when voltage is applied to B+.

You can pull modules (unplug) things like the PTO, IF deck, RF deck, and
see if it helps you isolate the problem down to a component in the power
supply or audio decks.

Just brainstorming this, but you can also temporarily put an inline
resistor into the B+ circuit (maybe at the fuse holder) to current limit
the B+ so you can do testing. Just remember that the resistor will need to
be able to dissipate 3/8 of an amp at B+ voltages so the wattage may be up
there (or a string of resistors in series). I would not do that for long.

I assume you do not have a capacitor tester so you may need to selectively
lift one leg free from each capacitor to see if it is the "problem child".
It will be a tough road to go (and frustrating) to "easter egg" and replace
components in any other way.

You can also pull all the tubes out of their sockets, I do not think that
is the problem (tubes) but it eliminates another bunch of components that
can be involved. Then you are down to just looking through resistors and
capacitors or some sort of short caused by a tinkerer.

If the PS and AF deck do not drive the current out of bounds then you can
start to plug modules back in.

-- 
Ms. Tisha Hayes/ AA4HA

*Republics decline into democracies and democracies degenerate into
despotisms.*

*-Aristotle*