Hitachi ARM series HDDs have a common breakdown, which shows that the former area of user area is accessible but the latter area is inaccessible. The behaviour is quite similar to Seagate partial access issue.

This problem is usually caused by replacing the original head with breakdown with a new head.After that this phenomenon comes up. That is to say, the user data in the beginning is readable, but from certain LBA, the rest becomes unreadable and error light indicator is shown with UNC light. This problem leads to the successrate of data recovery reduced greatly after changing head.

It's worth noting that Hitachi ARM HDDs have Partial Access Issue. The root cause is the donor head’s adaptive parameters couldn’t match well with the adaptive parameters of source head. Namely, the malfunction won't appear when adaptive parameters are compatible.

However,for some particular drives seeking a perfect donor head is not easy.At this time the problem is inevitable. To resolve this situation, you can use MRT tools.

Then we just seek a donor head as always. Swap head and see if this issue appears. When we meet this issue, use the recommended method so that it increases the successful rate of data recovery.

If you want to know the detailed procedure, please refer to the following link here:

http://vip.mrtlab.com/showdown.asp?id=10