My nikon fg shutter is stuck but only works when set on m90 or b

SOURCE: Nikon FG Shutter and light meter not working

Sorry, but there is nothing else you can do without dismantling the camera and giving it a full service. It's not a DIY job so will have to go to a repair specialist.

Note that unlike some similar Nikon models of the time, the FG's complex electronics mean that your camera may now only be good for spare parts as it's likely that the main circuit board has failed and replacements simply are not available and arevery difficult and expensive to fit if you're lucky enough to locate one. The reputation for failure of this model due to ageing circuitry means that it's now unpopular and near worthless.

A repair specialist can certainly tell you whether the camera is repairable before undertaking any serious work on it.

Personally, I'd just advise you to sell it as is for spares or repairs and to obtain a working example or even the mechanical Nikon FM/FM2 which are still plentiful, easily serviced and repaired, and available fairly cheaply or even free (via FreeCycle).

Testimonial: "Thanks Obertelli for taking the time for the detailed answer. I am hoping to keep the 50mm lens and hopefully use it with adapter."

SOURCE: Nikon FG. Replaced 3V

M90 is a battery independent setting - it requires no battery power to function. If it won't advance until put on M90 from other settings, then either you're not allowing for proper exposure, have the settings incorrectly set (film speed, etc), or you have shutter issues. The shutter is electronically controlled on all settings except M90. In the auto setting, your lense MUST be set to the smallest aperture (biggest number). On any other setting, you can use it however you'd like. I'd suggest unloading any film, setting the shutter speed dial to 1/125 or so, opening the back and looking thru and firing the shutter. If it's not snapping open and immediately closed, theres an issue and you need to consult a repair technician either locally, through Nikon, or through KEH Camera online.