Have a WD MyBook Studio drive here that had the wrong power supply plugged in. This damaged the hard drive PCB but I located a donor board and swapped firmware over and it now powers up and is recognized but of course I can't access data due to encryption. The bridge board on this particular model is part number 4060-705083-003 Rev A with Oxford encryption chip. Unfortunately it is also bad and does not provide power to drive. Normally I would just swap bridge board but I don't have any with Oxford chip, nor can I locate any suitable donor boards online. Any suggestions on testing / repairing the bridge board?

U2 is a serial flash memory. Perhaps you could try moving it to your donor.

U10 is a dual MOSFET. It switches +5V and +12V to the HDD under control of the bridge IC.

U4, Q3 and the 150K inductor appear to constitute a +5V DC-DC converter.

U6/L4 and the nearby IC/inductor pair constitute two switchmode supplies, probably Vcore and Vio (+3.3V) for the bridge, serial flash memory and the Firewire IC (FW843).

Measure the voltages at the V1, V2 and +5V test points. I would also check the zero-ohm resistor (L13) near the DC power socket.


APM4532, Anpec, Dual Enhancement Mode MOSFET (N-and P-Channel), 30V/5A, -30V/-3.5A:
http://www.anpec.com.tw/ashx_prod_file. ... M4532K.pdf
http://www.audiolabga.com/pdf/APM4532K.pdf

W25X40AVNIG, Winbond, 4Mbit, SPI serial flash memory, 3.3V:
http://www.darisus.de/Elektonikshop/Dat ... 25X80A.pdf

NX4110, Microsemi, 1A synchronous buck switcher with FET, 1MHz, SOT23-5L, 2.8V to 5.5V:
http://www.microsemi.com/document-porta ... 4110ds-pdf
http://datasheet.eeworld.com.cn/pdf/MIC ... 0CZ1TR.pdf

FW843, LSI Logic, IEEE 1394b Bilingual 3-Port Cable Transceiver/Arbiter, 3.3V supply, on-chip 1.2V regulator:
http://www.lsi.com/downloads/Public/139 ... _FW843.pdf (Product Brief)
http://www.lsi.com/products/networkingc ... FW843.aspx

OXUF943SE-LQCG, Oxford Semiconductor / PLX Technology, FireWire 800 or USB 2.0 to SATA Controller with Encryption:
http://www.plxtech.com/OXUF943SE
http://www.mouser.com/ds/2/327/roduct_B ... -16680.pdf

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This thread may have some related information:

viewtopic.php?f=1&t=26831

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First, thanks, as usual fzabkar, you always have excellent suggestions.

Unfortunately I don't have a donor for the bridge board, just hdd pcb otherwise I would take your recommendation and swap U2.

L13 resistor reports .1. I get no readings on V1, V2 and +5V test points. I get 12v on the top left two legs of Q3 (as seen in your enlargement in previous post) no readings on other legs.

If this provides any clues at all the Smooth chip on the original hdd pcb had been blown, with a large burn mark in the middle of the chip.

It's my understanding that these Oxford encryption chips were primary used on the this MyBook Studio Mac edition with USB 2 & FW800 ports. Perhaps I should look to just purchase another of these on eBay and hopefully it will also have the Oxford chip? Is U2 swap necessary on these bridge boards?

Thank you

AIUI, the +5V DC-DC converter provides the input to the V1 and V2 regulators. Therefore the problem may be confined to the +5V supply. That said, the NX2838 IC and AO4840 MOSFET are rated for 30V operation, so I can't understand why this section of the circuit appears to have failed. Perhaps your AC adapter had the wrong polarity?

Could you measure the TVS diodes on your HDD PCB? I expect that the 12V diode will be shorted, but it would be interesting to see if the 5V diode survived.

The diodes and zero-ohm resistors are identified in this photo clip:
http://www.hddoracle.com/download/file.php?id=1084&mode=view


Catastrophic failures in Western Digital PCBs:
http://www.hddoracle.com/viewtopic.php?f=59&t=1119&p=5033

TVS FAQ :
http://www.hddoracle.com/viewtopic.php?f=100&t=86&p=102

NX2838, Nexsem/Microsemi, 30V Adj HF Single Synchronous. Controller + 3.3V/500mA LDO:
http://www.microsemi.com/document-portal/doc_download/124276-nx2838ds

AO4840, ALPHA & OMEGA Semiconductor, 40V, 6A, Dual N-Channel MOSFET,
http://aosmd.com/pdfs/datasheet/AO4840.pdf

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A backup a day keeps DR away.