New circuit: Nikon Nikonos IVa-V
After the stop of the production of Nikonos IVa and Nikonos V from Ninon, many lucky people that has that camera canít find the replacement parts especially for the electronic parts. In this page I will describe a replacement circuit for a damaged original one, that allow the possibility to shot with times from 1/4 (1/8) to 1/125 sec.
The circuit not recover the TTL flash function. And the following described operation to assemble the circuit inside a camera is at own risk.
To understand how the circuit works, you must learn how the electromagnetic shutter unit works.
Inside the shutter unit there are four switch and one electromagnet. One of those is called TRIGGER it switch when the shutter is been armed and when the 1st curtain is fully opened. Another one is for the flash sync, and the last one used for the circuit is the release button that power on the meter when is half depressed, release the shutter when is full depressed. The electromagnet can hold the second curtain opened when is powered.
The timing is made by an electronic delay that power the electromagnet for the right time.
The circuit is made by two one shot circuits, one is triggered from the trigger switch and the other from the release switch. When the release button in fully depressed the shutter starts to open and the electromagnet is powered (for about one second from the monostable). When the one shot recive the reset signal the shutter starts to close. The reset signal comes from the other one shot triggered by the trigger switch. The right time to reset the 1st one shot is made by a comparator that receive a constant value from the ASA/ISO command and a ramp that start when the 1st curtain is totally opened. When the rampís value reach the constant one the reset command is given and the 2nd curtain starts to close (click here to download all related documentation, the PCB and schemes are in EXPRESS PCB format).