ususally when adding ajax in htmlOptions of an element binded on change function, check your page output by pressing ctrl+u on your page, something like this should be attached to that html element.
jQuery('body').on('change','#element_id',function(){/* check whether your ajax code is here*/})
try whether another change function for the same element binded.
code looks okay to me, we’ll debug it step by step, Okay first for temporally comment the $(’#umum_acc’) change function where you’ve written it, and then try whether $(’#Accoumdb_ACC_CODE’).change(function(){}) triggers with the right ajax url don’t pass any data just echo die in the controller ajax url action you should be able to see the echoed response in the firebug ajax post response;
Normally when value changes in the input field change event triggers. i think some javascript library or your very own code might be preventing event key code detection can you write jQuery(’#Accoumdb_ACC_CODE’) test change function or on keypress to this element whather you can get the out put if no values on these events you might have to check you javascripts and libraries.