Hello.
Our Client bring Us old SCSI HDD from Industrial device. Exact model (as in title): Seagate Medalist ST39140W. This is quite nice digital archeology case. I'm waiting for donor device and in meantime I want to ask You Guys and Girls, do You know are there any data stored on PCB (in this model) that need to be transferred to donor PCB? I don't see any separate eeprom chip (this device is from pre-flash eeprom era). It might be built in in other chips branded by ST (motor driver), NEC (heads stack controller?), SEAGATE (DSP/CPU?), SEAGATE LUCENT (CPU/DRAM controller/SCSI BUS controler?).

The firmware appears to be embedded within one or more of the micros, perhaps in a mask ROM.

Did you check the polyfuse and protection diode at the top left corner of the PCB?

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A backup a day keeps DR away.

I think on this old model you can just replace PCB w/o transferring any firmware.

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SAN, NAS, RAID, Server, and HDD Data Recovery.

Just above lower screw holes line, on the right side of PCB, tantalum capacitors surrounded there is SOT23 MOSFET that looks like it is burnt out (on the center of it there is something that looks like burn hole). I am waiting for working device to check voltages. On some fuses/diodes I have c.a. 5 V on other 0 V after power on, LM393 (upper central part near SCSI connector) is getting warmer, and Seagate 102069-501 chip too, no LED (down right to motor coils connector) blinks. On power plug, there is no short circuit on 12 V or 5 V and GND lines. Green poly fuse looks like shorted, but no other diodes/fuses are shorted. Without reference, working device I can't say anything interesting more.

The damaged MOSFET (or PNP transistor?) appears to be a P-channel type. There appears to be a "220" resistor between drain and source. I'm wondering whether this is a soft start circuit. If so, I'd check for a short circuit between drain and ground, just in case it could damage your replacement PCB.

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A backup a day keeps DR away.

Long story short.
PCB change works without any adaptation (this is very old SCSI drive).
After plugging HDD with new PCB to original controller, new PCB was destroyed by faulty controller or terminator. Before that, the image of drive was done (via different controller) with two soft badsectors, corrected by the drive itself. (Finally both were added to g-list). To say one more interesting thing, about this device - it was booting THEOS.
That's all about this Seagate drive. Now, the challenge is to build modern machine, that will use old ISA industrial controller, and run THEOS.