The Polaroid Land Cameras were originally designed to be used with flash bulbs and as such use what is called M-sync for the flash synchronization. M-sync fires the flash before the shutter opens (as opposed to X-sync which fires when the shutter is fully open) so that the bulb has time to ignite and illuminate before the film is exposed, this is problematic when using electric flashes designed for X-sync as the flash will have fired and dissipated before the shutter is open. My mod adds a small amount of mechanical delay to an X-sync flash so that it can fire from the M-sync flash output of the Polaroid.
With the front off my electronic flash you can see the internal wiring, the flash trigger wires are attached to the NO contacts on the relay. the extended Polaroid cable runs a white wire to the relay coil, and a black wire to the negative battery terminal of the flash. The positive battery terminal of the flash runs to the second relay coil to complete the circuit. The reason that i have opted to modify this flash as opposed to modifying the mechanical trigger switch inside of my Polaroid 350 is that i sometimes use the Polaroid bulb flash and would very much miss being able to use it.
The relay can be seen with a small ceramic capacitor across the relay coil terminals to reduce back-EMF (a bit paranoid, but generally accepted as good practice) The purpose of this relay is to provide an 8-12ms delay before triggering the flash (to make it approximately X-sync), this time delay is due to the mechanical limitations of the relays switching.
Inside of hot-shoe base, terminals have been kept for cosmetics and to act as tensioner when slotted into my flash holder. Be sure that the black wire from the original Polaroid cable runs to the negative battery terminal of the modified flash.
Hot-shoe base with wire grommet and an extended Polaroid flash cable. The original wires have been soldered onto and extended, and a new extended sheath has been added.
Flash with a relay fitted inside of the hot-shoe base. Extra wires to power the relay can be seen connected to battery tabs on the flash. If using a 3 volt relay, connect to the battery bridging terminal as shown, if using a 5-6 volt relay, connect this to the opposing battery terminal.
Here is my $20 Polaroid 350 with an odd handle that i found in an op shop for $3 and my now modified M-sync AGFATRONIC 301 CB that i got thrown in for free. The handle is great as it has a flash shoe, and still allows for tripod mounting as the retaining bolt is threaded.
