Looking for 5.25 drive replacements

[lowrybt1]

In connection with an effort to bring a C1PMF fully back to life, I'm investigating options for replacing/repairing the mechanicals and sensors on a MPI B-51.

I've determined that the Atari used the MPI B-51 mechanicals and sensors only for its 810 drive (1980's vintage). There is an outfit that sells these (drop-in mechanicals) refurbished and new-old-stock. Apparently, the Atari 810 did not use the index hole sensor so that needs to be added. And of course the logic board for the B-51 including data separator (all of which I have).

Has anyone tried interfacing the Atari 810 mechanicals to an OSI machine?

Thanks, Tom

[Klyball]

Hi Tom there a couple mpi b-92's on ebay they lowered the price on,

Grant

[lowrybt1]

Has anyone found a copy of the service manual for the MPI (Micro Peripherals Inc) B-92 floppy drive? I'm going to see if I can use it with my 600/610 setup in place of the B-51 that originally came with my C1PMF. First, I need to see if there's an attachment point for the MPI data separator daughter board. I think I see the plated holes in the B-92 PCB where pins might be attached for the data separator connection --but am not sure about it. I might try connecting the B-51 logic board to the B-92 mechanicals to what happens.

The issue with my B-51 appears to be:

* fault in the drive logic board that results in Track 0 error
* and/or fault with the Track 0 sensor/LED

On a related note.... I use the HxC SD card floppy emulator with my Sinclair QL and the thing is wonderful. Has anyone found a way to interface the HxC to OSI devices? It seems as if there is a lot of good info on the OSIWEB forum about physical and logic format of OS65D and OS65U on 5.25" disks, including timings and spacing. Perhaps the data-separator thing is a hurdle, though I think I've seen the HxC in use with TRS-80 Mod1, TI99/4 and Atari 800 setups and all of those had the need for data-separators (I think).

[Klyball]

I would just check the separator part of the mpi 51/52 schematic I would bet it will be the same /add your separator and cut this connection

To use the newer MPI drives without the separator board you must follow the trace from pin 30 to the 7438 NAND pin 3. Now follow pin 3 of the NAND and you will find it goes two places-
1. Daughterboard connector
2. pin 5 and 9 of the 74LS123
CUT the connection between pin 1 (NAND ) and the 74LS123

you can then modifiy the os65 to do 80 tracks later once its working/ as is it will just fill half the disk on one side like a mpi 51

Grant

[lowrybt1]

Hi Grant,

Thanks for sharing these instructions. I think they apply to the MPI-52, not the MPI-92. Would you know if the logic boards for the two models are similar? The 92 is an 80 track. The 52 is a 40 track, I think. Tom

[Klyball]

The logic boards for the 51 and 52 are basically the same it's just missing the head on the other side I would assume the only difference in the 92 is the step to get 80 tracks the osi will see it as drive A and drive B after you make the adjustments to the 610 board

So right now if you hook it up it will only use half of one side of the disk

Grant

[lowrybt1]

MPI B92 is interesting. It's 4 or 5 revs beyond the B-51 logic board and almost all the IC's and many of the traces are different. There's definitely a 10 slot header for the data separator daughter board to which pins need to be soldered. Also, it's single-sided.

The mechanicals are nearly identical to the MPI-51 and the cabling (P4 and P3 ) is identical so I'm hopeful that I might be able to interface the B-51 logic board to these mechanicals. If that doesn't work, I'll add the pins for the daughter board (J5) to the MPI-92 and see what happens when the data separator is connected to it.

[Klyball]

use the mpi 52 schematic and use a mutli meter to trace out the circuit to the separator you will need to snip a trace as above.