It is normal for a tape recorders heads to get a build up of dirt during normal use. Some cassettes are also prone to leave more dirt on a head than others, some cheap c90 cassettes will leave more oxide on a head than a more expensive brand, in general the blacker the color of the tape the better quality they are.

Symptoms of dirty heads include loss of treble, muffled sound, low volume and sometimes chewed tapes. To clean heads professionally you can forget about head cleaning tapes, these are good as a preventative measure only and may not clean away some of the caked on oxide that can accumulate on your heads.

First we need to do a visual inspection, 90% of units will have good access to the deck, if you open the door and look inside you will notice two or three things. in the middle there is a metal box with a rectangular strip on it this is the playback and record head, (if you unit does record) there will be a similar box on the left, this is the erase head and on the right is a rubber wheel below a shaft this is the pinch roller and capstan.

If there are any signs of brown oxide on the head or pinch roller its time to clean it up. some cassette doors will clip off to give you better access take a look at the side of the door when its open if it looks like it is a two piece door try to gently unclip by lifting upwards, if you cant unclip don’t worry about it as you don’t want to force it and maybe break it. next use some alcohol or maybe Mentholated Spirits on a rag or cotton bud to clean the head and pinch roller. never use any thing sharp or hard near the head if the oxide is caked on the head use a soft cream polish like silvo or brasso, never use steel wool. leave sit to allow pinch roller to dry out, then test. You should now hear an improvement in audio quality, most notably an improvement in the treble range.