help needed with tps51125

[rookieme]

I had power issue with a dell N5010.
There was no 3 or 5V.
The original part was RT8205BGQW and I have only the compatible tps51125.
I replaced is but still I get no power.
At pin 16 it gets the 19V but the vrefs are odd.
Pin 3 [vref] gives 1,2V - should be 2V.
Pin 8 [vreg3] gives 2,2V - should be 3,3V.
Pin 17 [vreg5] gives 3,3V- should be 5V.
0V at pins 11&20 [phase 2&1]
I also noticed that schematic mentions different configurations for each of the 2 alternative chips as they have different settings for TONSEL & SKIPSEL so I rearranged 2 resistors according the tps51125 datasheet but with no better result.
I replaced tps51125 again but same result.
What am I missing?

[cpt.charlie]

Re: help needed with tps51125

Check the resistance to ground of Vref Vreg3 and vreg5

[Djosla]

Re: help needed with tps51125

actually RT8205B is compatible with TPS51125A not TPS51125...output capacitance on ldo output is different...beside tonsel and skipsel that might be your problem...

[ridamouh159]

Re: help needed with tps51125

Tps51125=rt8205b=up6182

[Djosla]

Re: help needed with tps51125

Tps51125=rt8205b=up6182

Agree but this one:

TPS 51125A = RT8205BGQW =(CK=CD C47)

take a look at datasheeets...everything is explained...
lower voltage on 3.3 and 5v are definitely caused by either feedback lines or input refrence voltage...so check there...

[rookieme]

Re: help needed with tps51125

today the motherboard worked fine - for a while though
it was all night without power
after 5 minutes same issue..
too bad I don't have 51125A or RT8205B to give it a try - the owner won't give me time to make an order.


Thank you all for your time