Mac 1900 no volume up

I picked up a Mac 1900 which according to the seller had no volume. He had taken to his tech who said he didn’t have time for it now and so it was put up for several years. I was told it had no volume. I power the unit up and it did have volume but will not increase in volume. I cleaned the volume pot and it seamed to have made a difference in how long the sound came through as you turned the volume knob up. Near the half point of turning the knob you typically get a pop! I did plug and iPod into the power amp in and was able to get volume through, I was told this would test the amp but don’t know that to be true. I am not an audio person but competent so should take direction well. I’ve got 350 in the receiver and if I can get it working reasonable I’ll keep if not I’ll turn it. Thx