I have a 640GB 7200.11 drive that won't spin, won't warm up, doesn't output anything to terminal, nothing.

There appear to be two TVS components near the power connector. Both of them test fine (not shorted).

I have a 750GB 7200.11 drive and thought I'd use a DVM to make some comparisons.

When I get to the circled components, I find the board from the drive that works (the 750) measure about 400-Ohms in one direction, but nothing in the other (working like a diode even though they are in the circuit).

The drive that doesn't work, those components measure about 500-Ohms in either direction (working like a resistor).

Can anyone tell me what that part is? Are they likely both compromised, or am I finding a difference due to subtle board design differences, or is it likely that some other component has shorted and that is why the board that doesn't work reads 500-Ohms in both directions?

This drive was installed in a Maxtor external USB enclosure.

Thanks in advance for any help.

Shock sensor / motion detector

Thanks.

Well, I assume they don't have a memory, and that I have a problem elsewhere?

And even if they have a memory, I'm probably doomed if both of them are remembering the drive was dropped or something.

hmm it measures 2.4MOhm on the working Moose PCB and 48MOhm on working Brinks PCB
I assume 500Ohm is not what you need

But I also think those sensors have very high self-resistance, so 500Ohm is actually coming from PCB itself not the sensor
Did you take the sensors out of PCB when you measured them?

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No, at this point I was just trying to compare the readings at points on the board. I trust that off the board I'd get readings like yours.

Page 22 of the following datasheet shows what may be two typical configurations for a shock sensor amplifier.

Linear Technology LTC6240/LTC6241/LTC6242 Single/Dual/Quad 18MHz, Low Noise, Rail-to-Rail Output, CMOS Op Amps:

http://www.bdtic.com/DataSheet/Linear/L ... TC6242.pdf

Here are datasheets for Murata ceramic shock sensors:

http://www.farnell.com/datasheets/58860.pdf
http://www1.futureelectronics.com/doc/M ... 00LD-R.pdf

I'm thinking that the op-amps that amplify the signals from the two shock sensors have a shorted supply rail. This would explain why both sensors are testing the same in-circuit. I suspect that the op-amp's input has two ESD protection diodes, one connected to the positive supply, and the other to the negative (or ground).

The following ASCII art should be viewed with a fixed width font.

+V o---|<|---o---|<|---o -V (Ground)
D1 | D2
|
|
shock sensor
|
_|_
=

The shock sensor has nothing to do with a drive that doesn't spin up IMO.... the problem is elsewhere (but a 2 minute solution would be using another pcb to pinpoint the problem....)

IMHO, the OP has already found the problem -- s/he just isn't able to recognise it.

The first thing I would do would be to select higher ranges on the multimeter. This will prevent PN junctions from being turned on and thereby contributing to false readings.

The second thing to do is to spend a few minutes tracing out the circuit around the dual (?) op-amp, using the datasheet I provided. Then determine which power supplies are providing the V+ and V- for the op-amp, either the external +5V/+12V rails, or on-board regulators. If one of the on-board supplies is down, then the motor controller chip's POR circuitry would hold the PCB in a reset state.

The problem, unfortunately, is elsewhere

@cgallery, PM me or you'll lose a lot of time - send voltages at the relevant parts (RAM, MCU, common test points).

It would be quicker to measure the voltages at the V+ and V- pins of the op-amps (pins 8 & 4) on both drives.

Why? You assume the shock sensor part is the cause of a drive not spinning up. Never seen it and terminal would not lie about it.

No, I don't believe the problem is related to the shock sensors. The power supply to the op-amps appears to have a problem. This same supply rail probably supplies other components. Why look for test points elsewhere when pins 4 & 8 are available?

The OP could also compare resistances from V+ and V- to ground.

Completely wrong. But can't give any more details on open forum.

Of course you can't. The voltages at the op-amp are a trade secret.

If not, then you could always send me a PM. ;-)

Fzabkar, one of these days do the right thing : get a 7200.10 / 7200.11 scrap PCB, remove all the components and reconstruct the schematic. You'll find that ...... [censored] .

Take a good and a fried PCB and notice the differences in signals and states when working, when idle, with or without HDA.

Then you'll find the right answers - assuming the theory is right. Sometimes the good will and google are not enough.