Seagate 7200.12 stopped

[cLinic5]

Hello and thanks for all the help you have already been. I have

been studying the posts and learned a ton but I have a few

questions before I go soldering my drives PCB.

I have a seagate 7200.12 model ST7350528as, I like this model

number, it fits seagate for totally screwing their customers and

not even getting it completely fixed in the next series.

The drive has the firmware bug. Yes, I did part of the procedure

for 7200.11 drives and then changed what other 7200.12 users

suggested.

I had to try a couple of times before it saved everything and

exited.

Problem is the drive won't spin up. I read another post where they

mentioned that since the board isn't fully connected to the drive

there is excess electricity flying around. I think with how many

times I tried to do this I shorted something or I pushed it to the

limit. I didn't drop any screws on the board or anything like

that.

Now, after finding tons of stuff on the net, I am trying to test

the tvs diodes.

I am uploading a picture of my board. It has two shock sensors.

Can you test those?

Here are my results from testing the tvs diodes, the ones with the

red arrow under them. I used two digital voltmeters and one analog

volt meter. I looked on the board but could not tell which side

was the anode or cathode. I will list the results as R(red) lead

to the left side and B(black) lead to the right side of the diode.

B R would be when I switch the leads.

Digital Meter (both digital meters had similar results)

TVS 1 (diode setting) TVS 2

R-B 448 R-B 709

B-R pops up to 1400 then B-R 1 (a few times

goes straight to 1. it would pop to

1800 then go to 1)

Annalog Meter (this is where I get confused bec it's backwards and

I don't know the scale. I did zero the meter.

I have pics drawn but can't duplicate them so I will just give the

numbers and describe the position. If I get this right 0 on this

meter is to the right and the numbers get bigger as it moves to the

left.

TVS 1 @ x10 TVS 2

R-B needle moved up a R-B nada, didn't move

little around 500

B-R moved to four B-R moved to 9

TVS 1 @ x1k TVS 2

R-B shoots up to 10 R-B goes to 10 then drops to

then goes to 20 100

B-R moves to 3 stays B-R goes to 6 and stays

Digial Meter @ 200ohms

TVS 1 TVS 2

R-B 462 pops up then 1 R-B 960 pops up then goes to 1

B-R Stays at 1 B-R moves to 6 and stays

Can someone tell me if either of these are bad? If not what else

can I check. Thanks in advance for your assistance.

[jaclaz]

I presume that you are going after the wrong wild goose.

A TVS diode (though being a diode) behaves more like an "inverted" fuse.

The idea is that (in normal operation) it "bridges" the power line (either +5 or +12) to ground with "infinite" resistance.

If *something* triggers it then it shorts the power line to ground (thus switching off the PSU - if it has short protection - or nicely blowing some components on it).

You cannot actually test a "not triggered" TVS diode with an ohmeter (like you can't *any* diode) untill it is soldered to the board, of course if it was triggered and became a short you can detect the short.

The usual "repair" done when a TVS is shorted is simply that of removing it.

The board will have no protection anymore from survoltage or spikes, but it should work alright.

A drive not spinning is more likely to be an issue with the spindle bearing itself (but you had it spinning before) with contacts to the motor (but I guess that by now you have thoriughfully cleaned and checked them) or - as you fear - another component in the "motor driving electronics" that has blown up (current return, overcurrent due to poor contacts, etc.).

If the latter is the case, your best next move is doing a PCB swap, BUT you NEED and IDENTICAL PCB AND you MUST SWAP the ROM from the old board to the new one, something that is usually well beyond the soldering/desolering/resoldering abilities of the average DIY guy.

jaclaz

[cLinic5]

Thanks for the reply.

I think I have been chasing too many "wrong goose."

So by the numbers I posted can you tell if the TVS is shorted?

"A drive not spinning is more likely to be an issue with the spindle bearing itself (but you had it spinning before) with contacts to the motor (but I guess that by now you have thoriughfully cleaned and checked them) or - as you fear - another component in the "motor driving electronics" that has blown up (current return, overcurrent due to poor contacts, etc.)."

Yes it used to spin up and I did read and follow the posts on cleaning the contacts. Would it be worth removing the TVS before I send the board out for PCB and ROM swap. Notice I said send because I could remove the little ROM chip but I would never be able to get it back on<G>

Thanks again!

[jaclaz]

So by the numbers I posted can you tell if the TVS is shorted?

Hmmm.

I guess that the idea of "short" was not made entirely clear.

If the TVS diode is shorted, then the corresponding line is in contact with ground.

Try doing the following.

Get a pair of tweezers and put them contacting the two ends of a TVS diode.

Measure the resistance across the TVS diode (with the tweezers still there).

Remove the tweezers and measure again.

Did the reading change?

Simpler, connect the hard disk to a PC power supply (one with protection from short circuits).

Switch it on.

Does it automatically and immediately shuts down itself?

Yes=one (or both ) the TVS diodes are shorted

No= The TVS diodes are not shorted

jaclaz

Edited June 27, 2013 by jaclaz

[cLinic5]

Simpler, connect the hard disk to a PC power supply (one with protection from short circuits).

Switch it on.

Does it automatically and immediately shuts down itself?

Yes=one (or both ) the TVS diodes are shorted

No= The TVS diodes are not shorted

No tested it again with a PS that just has fans hooked up to it and it starts fine.

I want to try swapping it with another seagate board i have that used to start it

up but it gave a 0 or 8 mb size.

Will let you know how that turns out.

Thanks for the help.

[cLinic5]

Simpler, connect the hard disk to a PC power supply (one with protection from short circuits).

Switch it on.

Does it automatically and immediately shuts down itself?

Yes=one (or both ) the TVS diodes are shorted

No= The TVS diodes are not shorted

No tested it again with a PS that just has fans hooked up to it and it starts fine.

I want to try swapping it with another seagate board i have that used to start it

up but it gave a 0 or 8 mb size.

Will let you know how that turns out.

Thanks for the help.

Tested the other pcb from a working drive, also a seagate different size drives but same family.

Thank goodness it spun up the drive so i am happy no mechanical parts seem to be broken.

How would i identify what is bad on the pcb? Just downloaded a copy of "Tutorial - Linear and Switchmode Regulators used in HDDs by fzabkar"

and will be reading that tonight for some direction.

[jaclaz]

Tested the other pcb from a working drive, also a seagate different size drives but same family.

Thank goodness it spun up the drive so i am happy no mechanical parts seem to be broken.

How would i identify what is bad on the pcb? Just downloaded a copy of "Tutorial - Linear and Switchmode Regulators used in HDDs by fzabkar"

and will be reading that tonight for some direction.

The thing that is most likely to burn is the motor controller (often called SMOOTH chip), but normally it is evident by visual inspection (if that happened because of "too much current + bad contacts").

Example:

http://forum.hddguru.com/viewtopic.php?t=16737&start=

The usual procedure is however to find a "donor drive" with the EXACT SAME PCB and transfer the ROM chip from the old one to the "new" one.

jaclaz