Lots of times, old hardware comes with missing pieces. Sensors, controller boards, etc. etc.
This project's main goal is to remanufacture a logic board for an MPI Model 51/52 5.25" floppy drive, starting with nothing but the original scanned manual and a higher-end Model 92 drive for reference where the scanned schematics are too degraded.
Stretch goal: replace all TTL logic with a Raspberry Pi Pico, or some other equivalent microcontroller.
Unfortunately, I'm going to have to shelve this project. The only working drive I had, an MPI Model 92 Quad-Density drive, stopped working today, and I can't afford to keep sinking money into keeping it operational. Parts for it are becoming increasingly scarce, especially with items such as the read/write heads.
I'm unable to precisely pinpoint the issue with it, but I believe the IR LED for the index sensor has gone bad. I did find a modern equivalent for it (a TIL34 IR diode), but after having bought an MPI Model 52 drive (essentially a Model 51 like what this project was to be centered around, but for double-sided floppies) that turned out to have multiple points of failure, I'm feeling very demotivated.
This entire journey has spanned several months, and cost quite a bit more money in parts than I expected, mostly due to my one existing drive failing in increasingly-frustrating ways. The logic boards of the 92 and 52 are still in fine working condition, but the mechanical parts--the drive assembly itself, which is much harder to come by and/or remanufacture, has put the cost of completing this project far above what I'm able and willing to pay anymore.
(Also I still have made almost no progress on redrawing the schematics because screwit I'm too tired for this anymore.)
I think I'll instead use the knowledge I gained from working on this in the meantime on something different. I've recently had the idea of a modern cassette-based data storage drive over USB on mind, just because I can.
No progress has been made so far, BUT, I have two new developments:
I recently came across a far less-degraded copy of the original schematics. This should help clear up some of the confusion I've had in redrawing the schematics.
I may or may not have acquired a working Model 52, which is identical in all but the drive mechanism to the Model 51 that I intend to rebuild the logic board for. This should give me a good point of reference for what signals should look like.
I've been trying all this time to recreate the original schematic symbol for symbol, and holy crap has it been annoying to create symbols to match the original schematic.
I'm just gonna start using standard symbols instead and routing wires to the relevant pins. Save myself some headache and time for a project that wasn't meant to take up my entire summer break in redrawing alone.
This is a bit of an older screenshot, but my current approach to redrawing the schematic pages is to draw out a few components, then trace every relevant connection and component on a printout with a yellow highlighter to keep track of what's done and what isn't. As of writing this log, I haven't gotten past this stage yet thanks to my focus being centered more around overhauling my website. :P