It may indicate a polarity issue with your wiring. If the positive and negative are touching either in the rear of the unit or the rear of the speaker, RCHK will appear, as the system is attempting to avoid itself overloading it. In short, it's a safety measure designed to prolong the life of your unit.
this is the third unit ive had (htz520). it keeps blinking rchk. *** does that mean??? the first unit was ent in 3 times for repair in less than a year. they couldnt fix it so they exchanged it for a new comparable model (htz510). it was sent in for reapir twice before the 90 day warranty was up. so they gave me the htz 520. it apparently isnt going to work either. they need to go back to the drawing board and make something that works.