It's a Chinon FR-506 (NOT an FZ-506) Indeed, you have to be careful to put the right media and issue the proper density specific format command yourself, unless you work at the default of the drive, which in this case is HD. But I did, and I double checked the computer was outputting the right density signal on pin 2 on format and on write. Unfortunately the drive didn't respond correctly for writes in any settings I tried (auto or fixed density). On reading, from what I saw, the computer (at least mine) just tries both densities a couple times until it can read something. If there is some good data it declares success and keeps the pin 2 at the level that works for the rest of the session. There the news was better, the drive responded correctly to the pin 2 when it was set in auto, but incorrectly when it was in fixed HD (reading only in DD instead). So I left it in auto. At this point I'll declare this drive non functional, though still OK as a dual density, read-only drive... And look for a better HD one. My other 5.25" 360k DD 48tpi/300RPM drives read and write OK, so I have a working solution at low density. I want to recreate LIF drives for HP's, writing DD is what I need most anyhow. Thanks for the help, you pointed me in the right direction each time.