Laptop Toshiba Dynabook Satellite Pro C50-H-101 does not power up - Page 1
Forum section: electronics / repair

author: sdancer75
author_rank: Frequent Contributor
timestamp: August 20, 2023, 08:14:34 pm
content: 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?

author: fmashockie
author_rank: Frequent Contributor
timestamp: August 20, 2023, 08:22:58 pm
content: Here's the datasheet for LM2940https://www.ti.com/lit/ds/symlink/lm2940-n.pdf?ts=1692534539894&ref_url=https%253A%252F%252Fwww.google.com%252FBut 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.

author: sdancer75
author_rank: Frequent Contributor
timestamp: August 21, 2023, 07:19:02 am
content: Quote from: fmashockie on August 20, 2023, 08:22:58 pmThank you for your reply.The datasheet refers to another component. The actual component looks like thisthe 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.

author: fmashockie
author_rank: Frequent Contributor
timestamp: August 21, 2023, 03:40:20 pm
content: 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 herehttps://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.

author: fzabkar
author_rank: Super Contributor
timestamp: August 21, 2023, 09:59:50 pm
content: 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.

author: sdancer75
author_rank: Frequent Contributor
timestamp: August 22, 2023, 07:44:10 am
content: 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.

author: fzabkar
author_rank: Super Contributor
timestamp: August 22, 2023, 06:57:29 pm
content: The mystery part must be MP2940A.Attached is the marking code for an MP86905 for comparison purposes.

author: angourie
author_rank: Newbie
timestamp: April 29, 2025, 05:34:54 pm
content: hi!I have the same motherboard that I am trying to repair....Mine had a blown capacitor which upon trying to repair I managed to knock off an adjacent resistor.The resistor was damaged so I can't measure the value and there is no schematic that I can find.Any chance you still have the board, so you can maybe make a measurement for me?I've circled the part in the picture.It will be much appreciated!

author: sdancer75
author_rank: Frequent Contributor
timestamp: April 29, 2025, 06:15:47 pm
content: I am sorry but laptop was not mine so I had to return it to it's owner.

author: angourie
author_rank: Newbie
timestamp: April 29, 2025, 06:33:01 pm
content: Hi!Thanks for replying.Was it fixed?If not, do you think they might want to sell it for parts?I can't find any schematics whatsoever and the whole thing hinges on the value of that resistor....

author: sdancer75
author_rank: Frequent Contributor
timestamp: April 30, 2025, 06:54:00 am
content: I didnt repair it, but as long as I remember the problem was around CPU i.e capacitors or the CPU itself.

author: angourie
author_rank: Newbie
timestamp: April 30, 2025, 01:08:28 pm
content: In mine, the capacitor near the MP2940A you mentioned had blown (I circled it on you picture).The shorted capacitor took out the fuse F3 further up... once I replaced the fuse and the capacitor (couldn't find an smd one so I used a through hole tantalum one) the motherboard powered on...That capacitor is directly beneath the heat pipe so I suspect it gets overheated...The problem is that I accidently knocked off a resistor nearby, which unfortunately got damaged so I can't even measure it to get the value. It's important because it forms part of a resistor arrangement related to the voltage of the MP2930A. Since there are no schematics online, I am trying anyway I can to find the value of that part so I can replace it and fix that pc.I'll even repair it for the owner for free, if they let me have my measurement!

author: sdancer75
author_rank: Frequent Contributor
timestamp: April 30, 2025, 01:45:58 pm
content: If the resistor just below the one you destroyed is ok, why don't you try with this same value and check the result? They seem identical.Ps: check the voltage you should have in the inductors. You must have 1V for both of them.So according to this you can play with the replacement resistor value.

author: angourie
author_rank: Newbie
timestamp: May 01, 2025, 11:13:16 pm
content: They all look do look the same, all across the board actually, but they have different values...Those 2 resistors are both connected to pin 1 of MP2940A but go to different places after that so they probably have different values....I could try different values i guess, until it works, but I'll never be sure how the system is affected...BUTI did manage to find a faulty board on Ebay.... the fault is with the battery charging so this resistor should be fine... it was only £10!So when I get it I'll replace the resistor and I'll hopefully be on my way...I'll report back....