The Radio Information Board

I have a TK 480 that was working one minute and dead the next. The part if find odd, is that if you place a meter across the + and - batt. poles, there is no continunity...at all, with the power knob on or off. For comparison My TK280 shows about 3.5 ohms of resistance and my TK380 shows about 4 ohms with the power knob on, more with it off. Is there some sort of circuit breaker in there? If so where is it?

There is a fuse inside,F1 is a 3 amp fuse it is located on the side of CN10 which is near the A+ input.
mod