ROM chip question

[Ajay Kukadia]

Has anyone ever tried to fit a ROM chip to a P.C.B that has the ROM chip (details) embeded.
I ask because i have a a faulty Hitachi HDT721010SLA360 (wont spin up) and i cant read the ROM data from it. I Know the pcb is faulty as i have another identical model HDD and when I fit that pcb to my faulty drive it spins up fine.
I thought i could just swap the ROM chips over but the working pcb has the ROM chip missing and apparently the ROM chip is of the embeded type.
My question is:- If I fit the ROM chip anyway will it overide the embeded one or do I have to find exactly the same pcb.

Any help would be very appreciated.

Ajay

[labtech]

You seem to have one of the early version release PCB for that particular model drive.

First is not the ROM that need swapping, but rather the NV-RAM chip. Keep in mind that the PCB has a ROM as well, which is different than the NV-RAM.

Swapping the NV-RAM to the donor PCB is likely to mask the integrated ROM, thus bypassing it, so it should accomplish your goal.

With that said, there are some other compatibility issues that would need to be double checked on, such as the ROM version, then as result the PCB spec and so on.

Comment: should not swap test foreign PCBs on a drive as there could occur damage to the programmed code within it.

Question: have you tried fixing the PCB? E.g checked voltage protectors with a multimeter?

[Doomer]

My question is:- If I fit the ROM chip anyway will it overide the embeded one or do I have to find exactly the same pcb.

No, it won't
PCB needs to be configured to accept the ROM chip, usually it's one-two resistors close to ROM chip area

Post big enough pictures of both PCBs and you might find some help here to determine what else you need to move to new PCB along with ROM and NVRAM chips

[labtech]

Swapping the NV-RAM to the donor PCB is likely to mask the integrated NV-RAM [correction: not ROM as stated previously], thus bypassing it, so it should accomplish your goal.

[Ajay Kukadia]

Thanks for your help so far.

Sorry i did mean NV-RAM chip. I have checked voltages (marked with green dots on Faulty pcb overview photo attached) and all correct. There is no voltage output from the U3 chip, which I measured (marked by red dots). The only thing i have not checked yet is to see if the crystal is running, if it is not then the chip wouldnt work anyway. I am thinking that maybe there could be a dry joint somewhere, which could be cleared by a reflow of some of the pcb (but that is my last resort).

Ajay

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[Doomer]

both PCBs have NVRAM chip - U5
One PCB has ROM chip U7, the other PCB has ROM embedded to ASIC

If ROM revision is the same on both PCBs you only need to transfer NVRAM chip
If it is not the same you'll need to transfer ROM chip, as well.
Seems that capacitor on the top left conner of U7 chip, resistor on the bottom left conner of U7 and resistor to the bottom of U7 might do the trick with chip selection, that would be my guess

[Ajay Kukadia]

My humblest thanks for your help.

I swapped the NV-Ram chips over and then used the donor pcb on the faulty drive.
Fixed and working.

Thanks again

Ajay

[labtech]

Then that means the ROM versions were the same on both PCBs.
congrats