Laptop Toshiba Dynabook Satellite Pro C50-H-101 does not power up

[sdancer75]

I found that motherboard's +1.2v (memory power rail) and +1v (cpu power rail) are missing. An smd capacitor around M2940A IC (powers cpu and memory) and maybe the power regulator IC itself are shorted. +3v and +5v are ok and bios VIn is also ok.

I am thinking to replace the both IC and capacitors around them, but I don't know the values of them.

So, Is there any schematic of the motherboard and/or a datasheet for the M2940A IC?

Is there anyway to know that cpu itself is not shorted?

[fmashockie]

Here's the datasheet for LM2940 https://www.ti.com/lit/ds/symlink/lm2940-n.pdf?ts=1692534539894&ref_url=https%253A%252F%252Fwww.google.com%252F

But just because you have a short on this power rail, does not mean the problem is with voltage regulator.  It could be any component on that power rail causing the short.  You could use a multimeter with high precision (3 or more sig figs like a benchtop multimeter) to narrow down the location of the short on the board. 

[sdancer75]

Here's the datasheet for LM2940 https://www.ti.com/lit/ds/symlink/lm2940-n.pdf?ts=1692534539894&ref_url=https%253A%252F%252Fwww.google.com%252F

But just because you have a short on this power rail, does not mean the problem is with voltage regulator.  It could be any component on that power rail causing the short.  You could use a multimeter with high precision (3 or more sig figs like a benchtop multimeter) to narrow down the location of the short on the board.

Thank you for your reply.

The datasheet refers to another component. The actual component looks like this


the SMD capacitors around the IC are definitely shorted, so I suspect IC itself is also shorted. Testing pads just before MP2940A IC are getting +5V and +3V.

[fmashockie]

Sorry about that.  It appears to be an MPS (monolothic power systems) device.  I cannot find anything on it.  Searching their website doesn't yield any results.  The closest thing I could find is the MP2930 (link here https://www.monolithicpower.com/en/mp2930.html ).  It seems like it is an obsolete device possibly.  Might be worth reaching out to MPS directly for a datasheet if you need it, or a suitable replacement. 

[fzabkar]

Could the IC be a custom part? Could 465899 be a Toshiba part number? What are the date codes on the other ICs?

Maybe you could search for off-the-shelf ICs of that era at the Wayback Machine:

https://web.archive.org/web/20230000000000*/https://www.monolithicpower.com/

I suspect that the actual part number may be MPM2940A.

[sdancer75]

Thanks for the reply. I found some schematic block examples from monolithic that denotes the part as M2940A. Does not actually denotes the pinout but rather a draft block connection diagram.

The actual photos of the component are attached in this post.

[fzabkar]

The mystery part must be MP2940A.

Attached is the marking code for an MP86905 for comparison purposes.