Mamiya 645 pro help needed please

When my Grandfather died last year he left me his Mamiya 645 Pro with 55-110 lens which was working fine

Today I went out and NO matter WHAT I do when I chose a shutter speed in the AE prism finder it shows TOP DOWN

AV or SP (ok).
chosen shutter speed (ok)


However I am also getting "Lt" flashing lower left occasionally when I turn off and on again after a while and it will not go away no matter what combo of aperture/shutter speed

Chyanging from AP to SP makes NO difference

Help thanks

What is worse I can locate NO WHERE to have it looked at (Wales UK)

Super fresh batteries? Many cameras are very finicky about voltage...

Welcome to Photrio.
As Kino posted, replace the battery. Preferably with a silver oxide or lithium type, although in a pinch a really fresh alkaline battery can give you some use.
In addition, clean all the electrical contacts - the battery compartment, the finder, the film back.