Hitachi Deskstar Question

[Philip Shaw]

Good afternoon. I received a Hitachi Deskstar (HDP725025GLA380) which needed a head exchange and a PCB swap. I moved the 8-pin ROM chip starting with 25 from the customer board to the donor. The drive spun up normally but couldn't initialize. I ended up getting a second donor and changed the heads but still had the same issue. I swapped the PCB again and nothing changed. Both times when I put the heads that were in the customer drive back in a donor the donor worked fine. After a fair amount of flailing I checked the ROM chips from both donors and they are exactly the same. So the information I need to change over is stored somewhere else. Would that be on the main controller chip or on the other 8-pin chip? Is it just the NV-RAM that needs to be moved? The NV-RAM.nvr files from the donors are only 1KB but they do contain the serial number of the drive. If I can read the NV-RAM from the customer drive and transfer it to one of the donors will that do the trick?

Thanks.

[compos mentis]

Which PCB do you have?

What are the markings on the memory ICs?

I think some PCBs have the ROM in the MCU and the NVRAM in an 8-pin EEPROM.

[compos mentis]

Here are two versions of your PCB:

https://goughlui.com/wp-content/uploads/2023/02/2023012818174269.jpg

https://cdn10.bigcommerce.com/s-9c16le9g/products/16519/images/36260/IMG_8968__13907.1722067702.1280.1280.JPG

U5 is the NVRAM (S93C76).

U7 is the external ROM (25xx).

If U7 is unpopulated, then the ROM code is embedded within the MCU. The
ROM and NVRAM versions must be compatible. If the donor ROM and patient
ROM are different versions, then both U7 and U5 must be transferred. At
least, that's how I understand it. In any case, U5 must always be
transferred.

[Philip Shaw]

I have the second version with U7 populated. If the code that needs to be transferred is on U5 that would be great. All three ROM chips from U7 are the same so I don't know how important that is. But U5 is an easy transfer. I will give it a shot.

Is it your understanding that it is just the NV-RAM on U5 or does it have other adaptives?

Thanks.    

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[pbzcbf...@gmail.com]

The NVRAM has unique data, no code. The ROM has no adaptives, just code.