I have a Seagate Barracuda 7200.9 160GB drive that is dead, doesn't power on or spin up. I see what I assume are 2 TVS's on the PCB. Measuring these on the multimeter on 200k Ω the small one reads 16.8 and the bigger one reads 4.0

From research of other threads it seems that these are ok, as if they read zero then they could be the problem, but it doesn't seem so in this case.

At this point do I take it that PCB is game over? I can source an identical board, that's not a problem. However I assume I'm going to have to swap over the EEPROM. There are 3 8-pin chips on this PCB. Which would I need to swap, if that is indeed the correct step to take.

Any direction is appreciated.

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You need to read them in both directions.
The anode should read 0hm in both cases
and the cathode should give you reading similar to yours.

Test the +5 / +12 and make sure they are not 0ohm either.

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sorry i meant the TVS should not read 0hm on anode.

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The chip closest to the label is the correct one.

Bosse

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They read the same in either/both directions, 16.8 for the smaller one and 4.0 for the bigger one.


Not exactly sure what you are referring to here

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I thought it through and am having a guess that you meant the 2 resistors I circled below shouldn't measure 0 ohms. I measured them and they give the following:

The one on the 5v measures 15.75

The one on the 12v mearues 4.00

If these are all giving the correct readings does it mean there is something more seriously wrong with the PCB?

Thanks for the help

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Hi - +5/+12 is the main rails of the input - the golden fingers on the port where the power plug is.


Pin # Mating Function
— Coding notch
1 3rd 3.3 V
2 3rd
3 2nd
4 1st Ground
5 2nd
6 2nd
7 2nd 5 V
8 3rd
9 3rd
10 2nd Ground
11 3rd Staggered spinup/activity
(in supporting drives)
12 1st Ground
13 2nd 12 V
14 3rd
15 3rd

Please ground Balck pole and test appropriate pins. Should not Show 0ohm(short circuit)

I suspect you have faulty tvs diode

Please read this
http://en.wikipedia.org/wiki/Diode

Diode only works one way. Yours show a reading on both.

Please be careful before removing any protection systems. If not sure ask again.

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Got ya. Tested and didn't get a short on +5 or +12, got 16.75k Ω and 4.00k Ω respectively. That's a good thing then.


This speak of TVS diodes and measuring differently in different directions is confusing me. I understand that they are unidirectional etc, read up what I could on them. I've got access to loads of HDDs here, so I grabbed a few brand new ones now and tested the TVS's on them with multimeter set to 200kΩ. For each drive PCB i tested, the TVS's gave the same measurement irrespective of which direction I measured them.

Either I'm being a complete fool or my multimeter is possessed - both are quite possible

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The problem with testing TVS diodes in-circuit is that they are connected across the supply, which means that you are measuring the resistance of every component connected to that same rail.

If you measure the resistance of a diode out of circuit, then your readings will depend on the particular resistance range of your multimeter. On the "diode" or continuity test range, a typical digital multimeter outputs about 1mA of current at up to 3V. On the 200 ohms range my DMM outputs about 0.1mA at up to 0.5V.

A diode will conduct in one direction but not the other. However, the I-V (current - voltage) characteristic curve of a silicon diode has a sharp knee at about 0.6V.

http://chuck-wright.com/SolarSprintPV/Image8.gif

At voltages below this knee, there is very little conduction. This means that a diode will test as an open circuit on the 200 ohms range. However, on the diode range it will test as expected.

The problem with testing a diode in-circuit is that ICs and other active components (eg transistors) will have their own P-N junctions which behave essentially like diodes. Therefore the multimeter will be turning on these P-N junctions as well as the TVS diode's own P-N junction.

In any case, all you really need to know is whether or not the TVS diode is shorted, in which case it will be measuring almost zero ohms on any resistance range. That's why I suggest that people use the 200 ohms range rather than the diode test range.

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Thanks to all for the input. I've tested the board and the TVS's are not the problem. This drive is dirty and scratched and looks like the guy carried around with him in his bag or somewhere else unprotected so I'm thinking something bad happened to the board, maybe a zap of static or something. Either way the board is toast. I've ordered a replacement PCB and was told earlier that the EEPROM chip is the 8-pin closest to the barcode label, bottom left of the picture. I'm trusting this is right seeing that there are 2 other 8-pin chips on this board?

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I would have checked the health of the rest of the disk before wasting $$$ on a useless replacement board .... but this is another story

That appears to be correct. The chip will probably have a "25" in its part number.

My notes should help you identify the ICs:
http://www.users.on.net/~fzabkar/HDD/HDD_ICs.txt

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I would check the health of the other compents if I knew how, but at this stage I'm still very much in the learning stage. I've learnt a lot recently and hopefully I'll get to the "another story" soon I probably will waste some $$$ and drives along the way but that's all part of the learning curve isn't it.


Thanks Franc for confirming, it is indeed a M25P05VP, ST Microelectronics, 512 Kbit, Low Voltage, Serial Flash Memory chip. I'll swap it over when the new PCB arrives and see if I have any joy.

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I ended up receiving a donor pcb and swapped the rom chip over. The drive spins up now but the bugger is clicking. Until my pc3k arrives I suppose all I can do is post the terminal output. Could that help identify the problem? Maybe the heads are stuffed. Hard to say without being able to diagnose it properly.

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