Phonoland

Hi, 448 was working and playing records with good audio. Went to play a tune and after selection played a minute or so, the audio crackled and faded away to no sound and, I caught a hint of electronic malfunction scent. Now all I get is a popping sound I guess every second and a half to two senonds apart when record spins. Any clues or perhaps an answer? Thanks.

Sorry man--you (probably unknowing), have committed the "cardinal sin"--You let the smoke out !
Once done, I strongly suggest that you send the amplifier to a qualified, experienced repair "pro".
In any event, do not leave that phono plugged in, as, like in anything electrical, more damage can occur!
Ron Rich