It was once diagnosed at Nikon's service center and they said that the motherboard must be replaced.
As for power consumption, it will reset the batteries or rechargeable batteries in 2 days max. I checked on both of them. Everything else works great. I have the back panel of the MF 28 and there is no current going out of it
There used to be a recommended Nikon service in England. Unfortunately, I do not remember his name , but a lot of equipment people from Poland sent to him, because he was and cheaper and undertook repairs that in Poland service refused to perform - as a rule, in Poland they always wanted to replace the entire systems