no takers on this for far?? OK, I will give my 2cents even tho we dont mess with Yaskawa vfds. but the circuit is basically the same.... here is list of stuff to check from the top down:
1) next, they often have a parameter to turn this feature on or off; check that it is ON or it simply coasts to a stop as you have.
2) the db or regen if u prefer, circuit is simply a comparator op am that has DC bus voltage input as one and a 'setpoint' voltage as the other' sometimes the vfd lets u vary this as a parameter - if so, see if it is set correctly. on a 230v drive it is typically 390vdc turn on, 460 drive typicallly 750v.
3) next you need to have a resistor hooked up; u did not say size of this unit or if resistor is built in or not; if external, is one hooked up? if not, it will coast. dont have one? get 10pc 100w lite bults and wire them in series and hook that up - gives nice visual indication if the circuit is working
4) find the IGBT transistor that the comparator turns on; it is usually off to the side and easy to find as it is not part of the 4 output IGBTs. check it. You can ohm also to the db resistor terminals - it should wire to one db resistor terminal directly and to one dc bus on other side. the other db resistor terminal goes to the other dc bus side.
5) last thing if above does not get u going is to trace the input to the db IGBT to a circuit board and debug the comparator circuit. A failure i have see often is the input from the dc bus to the comparator: since the comparator works at like 10v and the dc bus is 300 or 600v, they need to drop this down; often done thru an obvious string of 10-20pc small 1/4 or 1/2 watt resistors - sometimes crud gets on pc board and can cause these to overheat and one smokes open.
6) If it does not get fixed and they want a new drive, I would be happy to quote you Hitachi!
BTW, the different resistance measurement on the output IGBTs is not your problem of course, but this is a bad thing; <usually> sometimes means they won't last as a set much longer.
let us know what you find!