820-00239 - switches on to 180mA only, no PPVCC_S0_CPU

[Vogelek23]

Hi, this one drives me crazy... No previous history, no signs of spillage, dust etc. (MLB looks like factory new). It does boost on all 4 ports to 20V, switches on to 180mA, drops down to 20-30mA and switches back on to 180mA then stays at this level. No PPVCC_S0_CPU although ALL_SYS_PWRGD signal is present on pin 48 of ISL (3.3V level). All other coils have the correct voltages (comparing to the table of measurements taken from working MLB). PPVCC_S0_CPU resistance to ground = 6 Ohm, no short circuit on any surrounding capacitor. Replaced ISL95828 controller and both SIC635 switches, no luck. What to do next?

EDIT 1: Checked with an oscilloscope and no single pulse at primary side of CPU coils when the MLB takes 180mA and ALL_SYS_PWRGD signal goes up.

 

[2informaticos]

CPU core is not only dependent of enable signal.
PCH, BIOS and part of CPU are all involved there.

Did you try known good BIOS?

 

[Vogelek23]

Did you try known good BIOS?

Thanks for your reply. Sorry I forgot to add EDIT 2. Yes, I tried known good BIOS, no positive result. Still the same, 180mA. Does it mean CPU has passed away?

 

[Mac Tech]

check the PWM signals coming out of ISL to the transistors?

 

[2informaticos]

If already tried BIOS, PCH/CPU should be the next.
Unless you detect a broken trace or damaged component on CPU area.

 

[Vogelek23]

After CPU reflow the MLB started with chime and picture. 2 minutes later it has switched itself off and went back to 180mA loop. Confirmed faulty CPU - no damaged componets/traces around CPU area found. Beyond economical repair. Thanks for the support!