HP 6720S starts with black screen

[mohkamtech]

Hp 6720s- platform: DDD UMA 6050A2137901-MB-A03

When started, fan spins continuously but no display on screen and external monitor.

Current reading : 0.003-0.48 and stopped at 0.68

Steps made :

Replaced ram, and cpu, with known good working ones, same problem.
Flashed bios, reflowed GPU for test purpose to no avail.

Tested mobo :
-CPU voltages :
Vcc_Core :+1.12V
VCCP : +1.18V
+V1.5S : +1.7V (a little high)
H_Pwrgd : +1.18V
H_Cpurst# :+ 1.8V

GPU voltages : +1.18V; +1.44V; +2.08V

All other voltages are present and measured good except :

-At CN17 (lvds connector) :
+V3A(pins 18-19-20) is missing due to "LVDS_VDD_EN" absent.
LVDSA_DATA pins signals are also absent.

-Bios (soic8) pins 1 and 2 always 3.54v strange !!!

Please advise as where to dig further ! Bios, I/O or other component !

 

[elektro-nik]

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Intel 965gm not respond to warming...

post card you have? Northbridge but most likely by replacing

 

[mohkamtech]

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No, it warms correctly. Cpu also.

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Unforunately got a pci post card, need e pcie.
Ordered a "Compal Diagnostic test card laptop motherboard". It's on the way.

Would you recommend any specific professional diagnostic card for laptop mobo ?

купите доступ для просмотра контента

Do you think that Northbridge might be so badly failing that a reflow won't help a temporarily fix ?

 

[elektro-nik]

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for your motherboard INVENTEC for many other the best, but not the only

купите доступ для просмотра контента

купите доступ для просмотра контента

COMPAL post card for motherboards COMPAL

Still there for Samsung and Asus, but the one that the link works with all except Compal

 

[mohkamtech]

So having both "Compal" and the 5 in 1 card you suggested is a complete diagnostic-set for lap mobos.

Some debug cards got lcd display, showing codes and solution for ami, award, phoenix and auto bios mobo, codes are up-gradable.

Thank you for the diag-card recommendation. I just ordered it from Germany.

PS : Are cpu and ram slot testers useful to speed up checking failed mobo ?
And is it better to get those with leds ?

Thank you

 

[mohkamtech]

PS do you recommend me to buy CPU and RAM slot testers for speeding the job ?

And if so, better get those with led or without ?

 

[elektro-nik]

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to check the socket on the continuity and insulation tester with LEDs use




for measuring signals and voltages using a tester without LED




to check the memory slots

 

[mohkamtech]

Thank you for you help elektro-nik.

As for hp6720s display fail, Northbridge has to be replaced as you concluded, reflow won't help. But lack of BGA machine, I think I have to give up!

 

[elektro-nik]

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for the repair of laptops need to have an infrared station ...

 

[mohkamtech]

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I have a "YAXUN-863D" infra_red station which I didn't experience yet . Is it enough to do the job of BGA replacement ?

 

[elektro-nik]

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infrared soldering station for motherboard

 

[mohkamtech]

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There are very pro ones with computer control. I'm intending to buy one in the coming years.

 

[mohkamtech]

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Hi !
I got it from Germany, tested hp6320s and got the error code 39. I'm not yet familiar with it. So P.S does this code pinpoint a specific failure ?


Thank you for responding.