This place is tricky to find. It's in a small plaza between Opera and Callao. There's a glass doorway with stairs leading downwards and the record store is down there (the glass doorway has a florescent machine gun on it if that helps.)
The shop has various rooms, but most of the records that are in some kind of order are in the main room with the cash register. Not super organized. They have lots of old Spanish rock, punk, vocalist records.
Open Monday - Friday 10:00-2:30 then 4:30-9:00.