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Old 10-12-2012, 01:11 PM   #1
spleenharvester
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Default HP 6735s shorted out - Multimeter time!

Had a 6735s brought to me. Would power off whenever it damn well felt like, usually when pressing the touchpad.

It eventually turned off while I was trying to figure out what the heck's wrong and would then only boot with black screen, 5 flashing caps lock lights and a flashing amber HDD light ("Unspecified system board failure").

Upon dismantling the laptop it's become clear a screw from the touchpad had fallen out and was wedged with the head on the pins of a DC-DC converter, model # Texas Instruments TPS51120, the pins in question are those facing north in the following picture (can take more pictures of surroundings if need be, but I couldn't get a good, focused picture of the whole board... my camera blows):

http://i.imgur.com/rcceZ.jpg

http://i.imgur.com/r0KTZ.jpg

Touching that area makes the laptop power off in the way it used to so the damage must have been done to that area, if not the TPS51120 chip itself.

Removing the screw stopped the random power offs, but now obviously, the thing is a brick.

Anyone know where to start? I've gotten various 5.0V and 3.3V readings from surrounding components..

Schematic for the chip is here: http://www.ti.com/general/docs/lit/g...US670&track=no

Cheers!

Last edited by spleenharvester; 10-12-2012 at 01:47 PM..
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Old 10-12-2012, 01:27 PM   #2
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Default Re: HP 6735s shorted out - Multimeter time!

Guys, made a bit of progress. (Picture flipped so it can be compared to schematic easily)

http://i.imgur.com/GxnTM.jpg

Also of note, the AC adapter jack no longer flashes blue when AC is plugged in, even though it appears to be charging from it. A humming sound also comes from the board with it plugged in.

http://imgur.com/kVgVW

Small red circle, just above the IC. Anytime the center of that contact point is touched with the DMM, the power cuts instantly.

EDIT: AHA! I think I found it. 7v reading back on V5REG (pin #21 on the schematic)

Last edited by spleenharvester; 10-12-2012 at 02:18 PM..
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Old 10-12-2012, 04:09 PM   #3
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Default Re: HP 6735s shorted out - Multimeter time!

Can't figure this one out at all. Power is getting to the RAM, NB, SB, CPU. But nothing is happening.

PGOOD1 also has the full 18v going through it. That's probably bad, because the max voltage is 6v.
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Old 10-12-2012, 05:44 PM   #4
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Default Re: HP 6735s shorted out - Multimeter time!

Aw, missed the post edit time, damn it.

Found Vref2 also has ~9v going through it when max is 6v. Is this basically a confirmed dead TPS51120 then? How likely is it there are other components in the chain damaged? How can I check?

Are there any areas I should be testing that I haven't already?

Also, a squealing sound came at the time the laptop died, though I couldn't see any magic smoke coming from anywhere.
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Old 10-13-2012, 04:21 PM   #5
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Default Re: HP 6735s shorted out - Multimeter time!

http://www.mediafire.com/view/?dy5b7eupc35k65y

^Laptop's entire schematic if that helps someone to help!!

TPS51120 is now completely dead if it wasn't already, accidentally shorted PGOOD1 with TONSEL (which should have been 2v but was actually 18v). Now PGOOD1 puts nothing out and there's no boot anywhere. Chip also gets scalding hot.

Still not really found much. Some readings I've scribbled down are as follows:

Code:
----------
Readings
----------

///TPS-51120 + Surroundings

+V5A, +V3A, +V3AL fine

+V5AL (lower) reading in at 7.2V!

+V5AL (side, pin 4) reading in at 2v!

VBAT reading in at 4.5v

R500 okay

///Test Pads

PAD1001/+V5A ok!
PAD1002/+V3A ok!
PAD1003/+V1.2S ok!
PAD1004/+V1.1S ok!
PAD1005/+VCC_NB reads 1.01v
PAD1006/+VCC_CORE_NB reads 0.78v
PAD1007/+V1.8 ok!


----------
REFERENCE/CHECK LATER
----------
SMSC KBC-1091-NU is the I/O chip
RS780
-Page 3 contains possible leads
These can be ctrl+f'd in the PDF.

V3A and V5A are the only readings I've managed to get from TPS51120, can't find the other components with which to measure it.

Trying to find out a bit more about the POWER_GOOD_3 signal. What reads it? What's generating the whole 5-caps-lock thing? Can't help but wonder if the big SMSC I/O chip is involved somewhere.

Last edited by spleenharvester; 10-13-2012 at 04:50 PM..
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Old 12-07-2012, 12:47 PM   #6
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Default Re: HP 6735s shorted out - Multimeter time!

Some progress guys.

Replaced TPS51120 today after an age of waiting for it to arrive. Fitted it, solder joints looking sweet if I may say so myself.

LEDs at charger point light up. Power button LED flashes briefly. There is a standby 3.3v voltage present, and the correct 18v in present (I have not checked any others for fear of shorting again).

But no response to power button. TPS51120 warms up, and eventually gets quite hot (though nowhere near as quickly as the last one did).

Where else could the problem be?
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Old 12-10-2012, 03:34 AM   #7
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Default Re: HP 6735s shorted out - Multimeter time!

This one is a bit tricky.
Where are you from? This boards are usually cheap, and i know i can get new one for less then 150€ (used ones for less than 100€) + shipping fees.
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Old 02-26-2013, 12:26 PM   #8
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Default Re: HP 6735s shorted out - Multimeter time!

Just thought I'd bump for anyone with the same issue to say I sold the motherboard as faulty/cheaps to someone on ebay not so long ago, it turned out it was U1018 that was the cause.
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Old 02-26-2013, 01:47 PM   #9
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Red face Re: HP 6735s shorted out - Multimeter time!

Quote:
Originally Posted by spleenharvester View Post
Just thought I'd bump for anyone with the same issue to say I sold the motherboard as faulty/cheaps to someone on ebay not so long ago, it turned out it was U1018 that was the cause.
what is U1018, I have searched scheme but no luck finding it, (I am not very good with schematics)
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Old 02-27-2013, 03:00 AM   #10
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Default Re: HP 6735s shorted out - Multimeter time!

dc/dc converter
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Old 02-27-2013, 04:46 AM   #11
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Thumbs up Re: HP 6735s shorted out - Multimeter time!

Quote:
Originally Posted by dj_ricoh View Post
dc/dc converter
Thanks dj
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Old 06-05-2020, 06:41 PM   #12
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Default Re: HP 6735s shorted out - Multimeter time!

Quote:
Originally Posted by trebo View Post
what is U1018, I have searched scheme but no luck finding it, (I am not very good with schematics)
friend can you help me with computer problem compaq 6735s
I already saw the u1018 pin vcc 4.95v and pin out 4.95v pin 1IN + 3.75v and pin 1IN-0v. but I still haven't changed the TPS 51120 AND IT GOT VERY HOT

Last edited by SMDFlea; 06-06-2020 at 05:23 AM.. Reason: google translate
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Old 06-06-2020, 02:14 AM   #13
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Default Re: HP 6735s shorted out - Multimeter time!

just throw it to bin. this ATI platform is useless to repair.

u will still need to rebal/replace ATI NB
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