thanks for the advice, do you know if this is a very expensive or difficult repair?

Hi everyone, I've recently acquired a beogram 4004 turntable. Everything on it has been working great until today when I tried to spin a 45 and found that it was playing too slow. It seems to play 33's perfectly, but when I put on a 45 its sluggish and out of pitch. Does this mean I need a new belt or is there some adjustment I could make? Thanks