I was looking for an answer to this same question and stumbled onto this possible solution at www.electronics-forum.info. I hope it helps:
Date: 22 Nov 2004 23:43:26
From: JURB6006
Subject: Re: 1989 Sears LXI TV
Try holding down vol+ and vol- at the same time (on the set, not the remote).
I'm not sure how long, 15- 30 seconds should do it if it's the model I think it is.
JURB
Sarah Vincent
January 2005