well in fact Access did replay to me very quickly and they told me that the correct part number is
ALPS EC16B 24 104 F 20
http://www.datasheetarchive.com/dl/D...ARS0024082.pdf
now i checked the web they r an old type hard to get
and also i do not want to replace them with the same cheap type
i want better ones with a metallic tree
but in fact any encoder 24 ppm should work
the only problem is that most of the new one are for panel mounting they are smaller
and they dont have the vertical mechanical fitting of the original ones
anyway the ec11 are smaller and they dont have 24 ppm
the ec12 do but they have plastic tree
http://www.mouser.com/catalog/catalogusd/645/1790.pdf
i am also looking at some bourns ones but if u panel mount them then u have to
solder an extension lead from the pcb to the panel possible but bit complex to do
Another quick fix is to just spray a contact cleaner in the plastic tree wait till it goes inside and turn them many times
it helps a lot and i have done it already but i still dont like the shaking nature of the plastic tree