Magnetic Head Assembly Failure
MHA is an abbreviation for ‘Magnetic Head Assembly’. This can also be referred to as HSA (Head stack assembly)
A magnetic head is approximately the size of a grain of sugar and can be found at the end of an arm that traverses backwards and forwards inside the hard drive chassis to read and write magnetic information to all locations on the rotating disk surfaces.
Modern hard drives have multiple storage surfaces, since each disk platter facilitates double-sided storage and higher capacity disks contain multiple disk platters. Each surface requires its own dedicated read/write head.
The MHA is a series of heads (one per surface) which move in unison, so that all surfaces can be read or written to simultaneously.
MHA Mechanical Failure
The system is somewhat similar in principle to a vinyl record player, though unlike a record stylus, the magnetic head(s) does not come in contact with the rotating platter(s). Instead, it ‘floats’ on a film of air generated by the rotation of the platter.
Any disturbance or shock to the disk while rotating can cause the heads to momentarily contact the rotating disk surfaces, resulting in damage to the heads and/or platter.
‘Head-only’ damage is usually a recoverable condition, whereas platter damage usually represents an unrecoverable condition.
One major problem in the determination of platter damage lies in the fact that in a multi-platter drive, it is generally not possible to visually inspect both sides of each disk platter during the data recovery evaluation process. Removing the platters individually will cause loss of rotational alignment of the platters as set during manufacture. Based on a number of other indicators, CDS will highlight cases where it is believed that a MHA replacement may result in a recovery of data. However, in these cases, there is always a risk that non-visible platter damage may damage the replacement MHA immediately, ultimately resulting in non-recoverability and an invoice for parts consumed.
MHA Electronic Failure:
The magnetic signals sent to and from the magnetic heads are very low in signal level, and need to be amplified. This is achieved using a pre-amplifier circuit which is also a component of the magnetic head assembly.
A voltage or current surge to the pre-amplifier can cause the pre-amplifier to fail, resulting in the necessity to replace the MHA, since the pre-amplifier is an integrated part of the MHA.
Obtaining a Replacement MHA
A replacement MHA is obtained by sourcing an exactly matched ‘donor’ hard drive which is disassembled to provide the required MHA part.
Exactly matched drives are sourced from specialist suppliers, usually in the USA or UK. Such companies stock and catalogue refurbished hard drives in a way that they can identify a correct match of critical hard drive attributes such as manufacturer, capacity, firmware revision and other key parameters.
Such specialist sources charge a premium for supply of donor drives, and there is usually a considerable cost element arising from expedited freight using services such as UPS/Fedex/DHL. Standard US post can take up to 4 weeks to reach Ireland!