Actually, I was looking for this information for 3 years!...now thanks to you, the manual is on my hands and of great help, cause I understand now where I was doing wrong connections and wires...excellent, I'll be back to you if in need, thank you.
This manual covers the main equipment features only. While it also includes the procedure for saving and loading from the now long obsolete memory cards it does not mention the how to operate with the optional floppy drive interface so I am still at a loss about how to use this! Note that there is a separate manual covering the MIDI interface and programming via the keyboard, not included in this download. You will also need to get hold of this if you want to use the MIDI interface properly. Basically there is little difference between this manual and the free to download manual for the similar PR60 model.
Good list of manuals. I found a very rare one and easily get. Should be promptly to download, as we must to wait hours even after confirmed payment.
Text excerpt from page 66 (click to view)
Appendices
Attaching the rack-mount adaptor
fig.um550
1. Remove three screws (on each side) from the right and left panels of the UM-550. 2. Using the screws you removed in step 1, attach the rack-mount brackets to the UM-550.
* You must use the screws that you removed. Do not use any other screws.
Attaching the desk-stand mount
fig.um550 fig.cushion
1. Remove three screws from the right panel of the UM-550. 2. Affix the cushion set (stickers) to the locations shown in the diagram at right.
Cushion set (stickers)
3. Using the screws you removed in step 1, attach the desk-stand mount to the UM-550. * You must use the screws that you removed. Do not use any other screws.
When standing the UM-550 on its side, make sure to position it so the power switch is at the bottom.