Sorry if I got you confused about 'different drives' - I'll try & make it a little clearer..
... but note that this is all speculation & guess work
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Depending on how old your Wii system is depends upon the type of DVD drive installed
The earlier Wii's systems had a 'standard' DVD drive fitted & this meant that they were capable of playing DVD movies, either by soft-modding or by hard wiring a 'Wiikey' to the drive itself
However since Nintendo didn't like this idea, they started modifying the drives to try & prevent this (IIRC there's been about 9 different variations of drives so far)
Although the drives may look identical - the controller chip is labelled differently [last few letters may be like "D2A", "D2B" etc] & it's possible that the firmware had been changed to try & prevent the 'Backup Disc playback issue
- I'm sure some1 will correct me if I'm wrong but AFAIK there are some combinations of DVD drives you can't swap with another. One such combo (I think) is that you MAY be able to place a D2C drive into a console that had an older drive BUT you can't put a D2B into a system that had a newer drive
(I found some of this info out from
this site)
Also even if you had a very old Wii & it went in for repair by Nintendo - it's possible that the drive was replaced with one of the newer versions which is incapable of playing movie DVD OR Disk backup disks
It's possible you may have 2 DVD drives that 'look' the same but your (broken) DVD may be a D2C & your (New) replacement is a D2B (an older drive) - or something similar
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Hope that clears some of the confusion up - but remember that I'm also only guessing that this might be the problem..... what is really needed is someone who knows more about DVD replacement & if there are certain combo's that won't work