It is worth trying to clean and lubricate your floppy drive mechanisms, as per instructions that can be found here and there, including from some of our members. I find that my floppy drives (particularly those that are not used regularly) are increasingly needing TLC these days. Most recently in one of mine, the motor driving the gear/spindle at the back that moves the heads had seized up, presumably due to dried up grease inside the motor. A small drop of oil was applied and allowed to penetrate the motor housing at the spindle, and bingo! it sprang into life. This drive was from a Power Macintosh, so it would not be surprising to see a CC-era floppy exhibit these or similar problems.
Sorry for the earlier misunderstanding. As for your troubles, some thoughts: 1) A 575 will accept a 128MB SIMM, and an LCIII will do so as well. What I am not sure has been established is whether a 550/CCII will accept one, but I can't see why not. 2) There is, however, still the question whether the SIMM itself is bad, or 3) whether the one you have in your hands is Mac-compatible. 4) The final thought is that you might need to wait a LONG time before the thing will boot while the RAM is checked, much longer than with the 8MB in there before. I am not sure about this, because I have no 128MB SIMMs, but others might be able to comment on the delay.
As for the fit that has been mentioned, I find that the 32MB SIMM in my CCII/550 is too tall also, and that it therefore needs to be inserted but not locked into place when the logic board is pushed into the machine, owing to the position of the screw receptacle on the CC's case. Once the logic board is in, however, I then use a chopstick or some such tool to snap it into an upright position. Removal is done by reversing this procedure. Very easily done.
Sorry for the earlier misunderstanding. As for your troubles, some thoughts: 1) A 575 will accept a 128MB SIMM, and an LCIII will do so as well. What I am not sure has been established is whether a 550/CCII will accept one, but I can't see why not. 2) There is, however, still the question whether the SIMM itself is bad, or 3) whether the one you have in your hands is Mac-compatible. 4) The final thought is that you might need to wait a LONG time before the thing will boot while the RAM is checked, much longer than with the 8MB in there before. I am not sure about this, because I have no 128MB SIMMs, but others might be able to comment on the delay.
As for the fit that has been mentioned, I find that the 32MB SIMM in my CCII/550 is too tall also, and that it therefore needs to be inserted but not locked into place when the logic board is pushed into the machine, owing to the position of the screw receptacle on the CC's case. Once the logic board is in, however, I then use a chopstick or some such tool to snap it into an upright position. Removal is done by reversing this procedure. Very easily done.