6735s - dead - more inside

[spleenharvester]

Hey all.

I have a 6735s motherboard here. Bought as "untested, fan was clogged so presumed to be cooked".

It was completely dead upon plugging in, no lights anywhere whatsoever.

Shorting the R1277, C1249 or leg 3 of Q1022 to ground makes the board work and boot fine.

Here's where it starts to get weird:

1) I had exactly the same problem with another motherboard, a 6715s which was also bought as dead, in this thread: https://www.badcaps.net/forum/showthread.php?t=27074

2) Not only that, the schematics are almost EXACTLY the same: 6715s schematic / 6735s schematic

I replaced transistor Q75 in the 6715s which did not resolve the issue so I assume Q1022 is not the problem here either.

I accidentally shorted the gain leg of the FDS6673BZ on the 6715s and blew it straight off, but after that, the board booted and worked fine (but obviously not "repaired").

Could it be that the MOSFETs are the cause of the problem in both cases? Or could it be C1249?

I'm certain my trusty Dell PA-10 is not at fault, it works fine in other laptops and has the exact same voltage/current/center-positive characteristics as the HP adapter. It also worked fine in the 6715s after the leg was blown off.

[spleenharvester]

Re: 6735s - dead - more inside

I'm tempted to replace C1249 anyway just to see what happens, I have plenty of spares on other dead boards. Is the replacement fine as long as it's 25v, 0.1uf?

Though having said that, I think the AM4825P may be blown.

[Tuomo]

Re: 6735s - dead - more inside

I'm tempted to replace C1249 anyway just to see what happens, I have plenty of spares on other dead boards. Is the replacement fine as long as it's 25v, 0.1uf?

Though having said that, I think the AM4825P may be blown.

I thin you should measure this capasitor if it is fail.

Problems seems to be at Q1022 not take Q1031 PIN 4 to LOW.

Can you measure Q1022 PIN 1, 2, 3, then you see if Q1022 open or not.

It may be at ADP_EN# signal is not low then Q1022 not open.

When you short those pins then Q1031 PIN 4 go LOW which OPEN it.

[spleenharvester]

Re: 6735s - dead - more inside

ADP_EN# measures in at 8.64 volts, as measured from diode D1010's positive side ("1" on schematic). I am guessing this is where the problem lies, then?

D1010's negative side reads a full 18v.



Q1022 appears fine I'll take a better look tomorrow when my DMM is fixed up.

[spleenharvester]

Re: 6735s - dead - more inside

More on above

D1010's negative side - at ADP_EN# - reads a full 19v (sorry info in above post was incorrect)
D1010's positive side reads ~8v.
R2006 reads also a full 19v.
I may be wrong but ADP_EN (not ADP_EN#) reads in at 0v.

Just found out, when C1249 is shorted and the board booted, it gives the 5 flashing caps lock of death - "System board failure" - could this be because there's no CPU or memory? Or is the board just a dead case and not worth bothering with?

[Tuomo]

Re: 6735s - dead - more inside

More on above

D1010's negative side - at ADP_EN# - reads a full 19v (sorry info in above post was incorrect)
D1010's positive side reads ~8v.
R2006 reads also a full 19v.
I may be wrong but ADP_EN (not ADP_EN#) reads in at 0v.

Just found out, when C1249 is shorted and the board booted, it gives the 5 flashing caps lock of death - "System board failure" - could this be because there's no CPU or memory? Or is the board just a dead case and not worth bothering with?

When shorted C1249 it boots cause Q1031 PIN 4 go LOW.

I think you should focus on ADP_EN# signal.

ADP_EN# should be LOW and ADP_EN should be HIGH.

It looks at AC Adapter not recogniced.

[spleenharvester]

Re: 6735s - dead - more inside

It was the adapter all along. It wasn't sending LIMITsignal and when it's shorted with the 19v supply, everything works.

So I've blown a 6715s for nothing, and the one I didn't blow, has 5 flashing lights of death.

****'s sake

[spleenharvester]

Re: 6735s - dead - more inside

I think I'm gonna get to work on fixing this 5 caps lock + amber flashing issue.

https://www.badcaps.net/forum/showthread.php?t=23141 I had a similar fault before and gave up and sold it to someone - U1018 turned out to be the culprit. But in this case, U1018 appears to be okay.

Pressing hard on the BGA chips and powering the system does not help so it does not appear to be the southbridge BGA issue this model can suffer.

TPS51120 appears to be okay because there are a multitude of 5v, 3.3v and 2.5v sources around the board.

DDR2 power is fine, CPU Vcore is fine, +5v and +3.3v rails are all fine.

BIOS chip is receiving power.

CPU, NB, SB and KBC1091 I/O controller all warm up on booting.

There's one odd thing I've noticed; sometimes, when booting, the amber HDD light flashes repeatedly. Other times, it will flash twice as fast.

I wonder where these LED flashing codes are being generated from?

[Tuomo]

Re: 6735s - dead - more inside

I think I'm gonna get to work on fixing this 5 caps lock + amber flashing issue.

https://www.badcaps.net/forum/showthread.php?t=23141 I had a similar fault before and gave up and sold it to someone - U1018 turned out to be the culprit. But in this case, U1018 appears to be okay.

Pressing hard on the BGA chips and powering the system does not help so it does not appear to be the southbridge BGA issue this model can suffer.

TPS51120 appears to be okay because there are a multitude of 5v, 3.3v and 2.5v sources around the board.

DDR2 power is fine, CPU Vcore is fine, +5v and +3.3v rails are all fine.

BIOS chip is receiving power.

CPU, NB, SB and KBC1091 I/O controller all warm up on booting.

There's one odd thing I've noticed; sometimes, when booting, the amber HDD light flashes repeatedly. Other times, it will flash twice as fast.

I wonder where these LED flashing codes are being generated from?

I think KBC and South Bridge.

You can check few signals.

RSMRST = 3V, SB_PWRG = 3V, KBC_SIO_RST# = 3V.

RSMRST when 0 reset South Bridge.

SB_PWRG KBC voltages OK.

KBC_SIO_RST# when 0 reset KBC.