5.25 floppies that read but don't write

Chuck, I looked at the pin 2 signal and resulting drive behavior. It doesn't properly auto-switch between densities as it should. It does switch it for reading, but not for writing. Below is the full story. There is one jumper that controls DD/HD switching mode. In the auto position, I can read both HD and DD formats (I use the right diskettes for either format). You can see the computer on pin 2 (density select) trying both positions, settling on the right one (high for HD, low for DD), and reading the disc correctly. That's great. But when writing, although pin 2 goes to the right level, the floppy seems to ignore it. It will always write at DD, and refuse to write in HD (no signal at the head). Interestingly, in the fixed density position (should be HD only), it WILL write at 1.2M HD! The write signal does appears at the head. Unfortunately in this setting it will NOT switch the reading, get stuck reading only DD and fail on HD. So I can either have the reading HD or the writing HD, but not the two at the same time. That's why a regular format fails. The density switching logic seems to have a problem. Rather than track down which IC or transistor failed on the board it might be much simpler to get another 5.25 floppy. In the meantime my understanding of these simple critters has improved a lot. Marc