Sometimes, the cleaning light pops on when the tape itself cannot be read. I would turn it off, then back on, and see if with no tape, the light stays off. See if teh light only pops on after a tape is inserted, and it makes a buzzing sound.
If you have this attached to Windows XP pro, you have a backup application that is included for free. What I have done many times, is to take a problem tape, and insert it into the DLT drive while that backup application is running. It takes about 3 minutes or so but the tape application will finally say that the tape can’t be used unless it is prepped. Do I wish to prep it. I of course say, yes, please, blow the mo fo away.
After a minute, the tape is all good. I unload the backup application and my pre-mastering software loves the tape again. This doesn’t work all the time, but it does help much of the time.
I see this issue mostly happen when you buy used tapes. Who can blame me. Used tape cost as little at $3 and new tapes are $34 to $44. So its worth it sometimes to buy a few used tapes. I mention that, because if that’s what you did, expect many of them to just not work. I see that a lot, but I continue to buy them as much of the time they do work, and the ones that don’t do not offset the cost ratio beneifts enough to stop me from doing this.
NOw, if you did all that, and it still doesn’t work. Try a brand new tape. A Maxell Type IV can be purchased for $34 new if you shop around. Try newegg.com. If that still doesn’t work, then it could be just about anything. Try lower grade tapes. Sometimes a Type III will work where a Type IV fails. If that doesn’t work, then the DLT board could be bad, or dust may have found its way into teh head area, which is enclosed, but not air tight or anything. Dust can get in there. I don’t know that I would look to get one repaired as they cost so little on ebay, it might be worth it to just buy another one. Still, you could always type DLT repair in Google and see what pops up.