http://www.digoliardi.net/electrics2.gif

I am dangerously ignorant of electrics so I'm asking: How does it work
that one AC pole goes to one pole of the orange thing (capacitor?) and
then also go around it? It's there a short there?

No, the capacitor is charge from the AC line with a resistor and a
rectifier diode.

You have some problems here that will cause trouble down the line:
1) I am assuming that "TR R210" is a rectifier - the number comes up with
zilch when googled. It should be rated 700V (~2x Vp-p) or greater. The
standard popcorn part would be a 1N4007.

2) The capacitor needs to be rated for a minimum of 200VDC continuous - it
will charge to 170V in this circuit.

3) You should have a fuse in the circuit. It is hard to say what size
without knowing the solenoid rating. If the Lectrohm is rated for 5W then a
good guess is the circuit needs about a 1/8 amp with the shutter closed. A
1/4 amp slow-blow fuse should be adequate. If you don't have a fuse, and
there is a short in the shutter solenoid or capacitor, then there will be 33
watts dissipated in the Lectrohm. This is a very unfortunate number if the
Lectrohm is rated for 5W - the Lectrohm will get yellow hot but not fail and
you have yourself a fire starter. You should test the fuse, making sure it
will blow, by shorting the solenoid and closing the switch: make sure the
fuse blows before smoke starts to rise from the Lectrohm. The fuse gets a
bit of a workout in this circuit and may fail from fatigue every few years.
In lieu of a fuse you can use a 50W Lectrohm.

I am assuming the circuit works as follows, though I have no idea of the
shutter solenoid's ratings, so some of it is guestimation:

The capacitor is normally charged to 170V and it sits there at this voltage
until the shutter is switched on. No current is drawn from the 120VAC once
the capacitor charges.

When the switch closes the capacitor provides a shot of 170V power to close
the shutter solenoid.

Solenoids need a lower voltage to hold closed than they need to activate. By
reducing the holding voltage the solenoid coil can be made smaller - the
solenoid doesn't have to be sized to take full voltage all the time.
Continuous full voltage will overheat the coil in a solenoid designed to be
used in this fashion.

When the shutter is closed, and the capacitor has partially discharged, the
circuit provides a much lower current to hold the solenoid closed. The 200
ohm resistor drops some of the voltage going to the solenoid and capacitor.

When the switch is opened the shutter solenoid opens and the capacitor is
charged back to 170V for the next shutter closing. The recharging takes less
than half a second.

Connecting the circuit to a timer:

First, a problem: a timer is wired to supply 120V when exposing. You can't
wire the timer's socket across the switch without major pyrotechnics.

The "standard" way to connect this circuit to an enlarging timer would be to
leave the switch closed and plug the 120V leads into the timer. This may not
work very well.

If the timer controls the 120V then the capacitor doesn't get fully charged
and the shutter solenoid doesn't get a high voltage kick to slam it closed.
Without the higher voltage the solenoid may not work or work sluggishly and
erratically.

You need to wire a relay where the switch is located - the coil of the relay
goes to the timer and the relay contacts are wired across the switch. You
need a SPST relay with a 120VAC 60Hz coil. You can get one at Radio Shack.


--
Nicholas O. Lindan, Cleveland, Ohio
Darkroom Automation: F-Stop Timers, Enlarging Meters
http://www.darkroomautomation.com/index2.htm
n o lindan at ix dot netcom dot com