Seagate HDD repair and data recovery has its own clue to follow and find the best solutions with the right hdd repair tools.

Lack of spindle rotation
The problem can be caused by a damaged PCB (in particular, the spindle motor controller chip), short circuit of coils (which can be checked by a measurement of the resistance on the HDA contacts), motor seizure, oxidization of the contacts between the controller board and the spindle motor contacts on the HDA. Solution of the problems with a seized spindle and s/c motor coils only makes sense when you need to recover data. In case of a short circuit you can attempt to use a resistor in order to “straighten” the s/c motor coil or consider moving the disk to a donor HDA.

Endless <>, “HM …” output in terminal
The malfunction can be caused by a burnt-out commutator chip or lack of power supply on the commutator connector. In case of such problem you should examine the drive checking it for signs of a short circuit, probe the commutator connector between the PCB and HDA. Compare during the procedure the resistance values between the power supply contacts of the commutator and ground and the corresponding values for a normal drive. Then attempt to use a functional PCB to check the drive. You can also check whether +/- 5V power is supplied to the commutator connector of the drive PCB. You can find out the exact contacts where it should be present using a functional board or tracing the power supply components on the board.

Fix Errors “unknown preamp type” or “preamp not supported”
The message means a damaged commutator, a non-native board or erased content of the Serial Flash ROM on the PCB. You can check whether the ROM is erased by reading it.

No response in terminal at power-on
You need some professional hdd repair and data recovery tools like PC3k or HD Doctor Suite to test on this one.
In that case drive PCB is either damaged or hanging because of a malfunctioning commutator chip. You can use the native board for a check – insert insulating material over the commutator chip, install the PCB over the HDA and switch power on. If messages in terminal appear, there is a problem with the commutator. You can use a donor board, but please check the HDA first for a short circuit on the contacts of commutator power supply and heads positioning device control. If a short circuit is present, replace the magnetic heads assembly with the commutator.

Serial Flash data corruption
Corruption of data in HDD Flash memory is a rather common case. In Seagate HDD families equipped with
Serial Flash (see section 4. Overview of firmware structure in Seagate Barracuda drives) you can do without a programmer device, unlike the families based on Parallel Flash. To do that, you have to switch a drive to Safe Mode and then rewrite Flash in the utility in Safe Mode. In the simplest case you will have to send a Safe Mode signal in the utility (from its start-up dialog or from utility status dialog) and switch on the drive’s power supply (or use the Safe Mode initialization toolbar button for automatic switching). The HDD at that must switch to terminal level “F>”, then you may proceed with ROM rewriting. In a more complicated situation (e.g., when area containing the interrupt table is damaged) a drive may enter an endless loop while outputting the contents of controller register, then it will not react to Safe Mode signal. To solve the problem, you have to short-circuit pins 4 and 5 of the Serial Flash chip (see the figure below).

Fix ”Application code incompatible with serial flash code”
The message can be caused by a non-native PCB (or just Flash content), or by App code read from disk surface
incorrectly (e.g., because of heads contamination). You can attempt to read and analyze App code from disk surface. If readable information is retrieved, find in App body the <<Eng Rev>> string and use the text string of firmware version next to it to decide after analysis of statistical information (please see an additional appendix hereto), which ROM version is native for the drive. The required ROM version is often indicated in new drive families next to the <<Eng Rev>> string.

There are more about the Seagate HDD failures and solutions, please read here

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