Help identifying a component - M091 SOT23 (?) - Page 1
Forum section: electronics / repair

author: Nexxen
author_rank: Regular Contributor
timestamp: March 29, 2023, 11:28:35 pm
content: I need to identify a component:3mm x 2mm2 legs on a side, 1 on the other (SOT23?)Has M091 on top.Two leads have +5V, the side with one had 0.Thanks in advance!!

author: fzabkar
author_rank: Super Contributor
timestamp: March 30, 2023, 12:27:53 am
content: http://www.smdmark.com/en-US/search/code?id=m0Try m0, mo, m09, m09, m0xx, etc. There are numerous permutations.It would help if you were to tell us its circuit reference, eg Qnn, ICnn, Tnn, etc.

author: Nexxen
author_rank: Regular Contributor
timestamp: March 30, 2023, 12:52:59 am
content: No idea what you are talking about. Unfortunately those are unknown acronyms.It's on a motherboard, close to ram.I'm a beginner, I know I'll be both dasappointing and frsutratingI'll post pictures tomorrow.Thanks

author: fzabkar
author_rank: Super Contributor
timestamp: March 30, 2023, 01:00:37 am
content: A component on a PCB is usually identified with text such as IC123 or U123 or Q456. "IC" and "U" are used to identify an integrated circuit, whereas a "Q" identifies a transistor, "C" = capacitor, "R" = resistor, etc.

author: Nexxen
author_rank: Regular Contributor
timestamp: March 30, 2023, 01:04:59 am
content: Q748 (Q is the important info I guess)Thanks, I never thought it actually mattered. Ok, C and R I knew

author: fzabkar
author_rank: Super Contributor
timestamp: March 30, 2023, 01:15:51 am
content: Quote from: Nexxen on March 30, 2023, 01:04:59 amI'm guessing it's an enhancement mode P-channel MOSFET.If the voltages are 0V, 5V, 5V from left to right (centre pin at top), then the MOSFET is being switched on.

author: Nexxen
author_rank: Regular Contributor
timestamp: March 30, 2023, 01:10:23 pm
content: PicsComponents  goes to [WW1 P6]In pic 3 the 0V pad of M091 goes to Q747 (60N3L) mosfet, sharing it with componets PQ1 (D90N0 2L). On the left of the RAM slots.I can't make where Q747 and PQ1 get their Vcc. Probably needs to be enabled.https://pdf1.alldatasheet.com/datasheet-pdf/view/171603/STMICROELECTRONICS/D90N02L.html

author: Nexxen
author_rank: Regular Contributor
timestamp: March 31, 2023, 12:50:05 am
content: I couldn't find a match.I'll write to Asrock and hope they'll give me the answer.I'm wondering if such a small component can be responsible for the whole board to power on.

author: Nexxen
author_rank: Regular Contributor
timestamp: April 01, 2023, 01:39:55 pm
content: AP2309GNhttps://www.alldatasheet.com/datasheet-pdf/pdf/146907/A-POWER/AP2309GN.htmlCould this one do it? I found it on another board, and it takes both +5VSB and +5V on the other, like my board does.

author: fzabkar
author_rank: Super Contributor
timestamp: April 01, 2023, 08:12:20 pm
content: Quote from: Nexxen on April 01, 2023, 01:39:55 pmI'm confused. Your original hand drawn diagram shows that the MOSFET is connected to the PSU's Power OK signal (which is open collector), but now you are saying it is connected to the +5VSB standby supply.

author: Nexxen
author_rank: Regular Contributor
timestamp: April 01, 2023, 10:23:16 pm
content: That's a mistake on my part.It's indeed +5VSB.My apologies.

author: fzabkar
author_rank: Super Contributor
timestamp: April 01, 2023, 11:13:48 pm
content: Before replacing the MOSFET, I would check the other connected components to confirm that there are no shorts to ground, or any other reason for the failure.

author: Nexxen
author_rank: Regular Contributor
timestamp: April 01, 2023, 11:35:01 pm
content: There were two burnt components:- the mosfet- a traceThe trace was rebuilt and no shorts, no dead shorts on PWR connector nor other components.No shorts whatsoever anywhere. Checked again now.This doesn't mean it may not die.

author: fzabkar
author_rank: Super Contributor
timestamp: April 02, 2023, 12:30:51 am
content: It looks to me as if the MOSFET is configured as a power switch. Maybe you could install a fuse between drain and source, and then see what happens?

author: Nexxen
author_rank: Regular Contributor
timestamp: April 02, 2023, 12:46:35 am
content: The side with one pin,- goes to a mosfet that on one leg then goes to power on the PS/2 connectors and other two components further down.Without this it won't output the necessary V to PS/2 and those components.To me IT IS linked to the switch on circuitry.What kind of fuse? Values to suggest.Sorry if I'm boring but I'm really that low on electronics knowledge, albeit with much enthusiasm!

author: fzabkar
author_rank: Super Contributor
timestamp: April 02, 2023, 12:50:50 am
content: Maybe 0.5A or 1A fast blo? I still have a feeling that you've missed something. For example, if a MOSFET dies with a short between gate and source, then whatever IC is driving the gate can often fail, too.

author: Nexxen
author_rank: Regular Contributor
timestamp: April 02, 2023, 01:03:25 am
content: This might take some time, I have to order them on aliexpress.Fast blowing smd 0.5A any voltage?Thanks for the help so far!!

author: fzabkar
author_rank: Super Contributor
timestamp: April 02, 2023, 01:10:23 am
content: Voltage doesn't matter. I'm not suggesting that you make this a permanent fixture. I'm simply suggesting that you wire an ordinary glass fuse between drain and source for testing purposes. Then, after you are sure that there are no other faults, you could replace the MOSFET.Alternatively, you could use a momentary pushbutton switch plus fuse attached via wires.

author: Nexxen
author_rank: Regular Contributor
timestamp: April 02, 2023, 01:24:30 am
content: There was a big bulge on the S/D side of it. Could have it been an overload from PS-2 or the previous owner touched the trace and it created some loop?Like when you touch a trace with a metallic object and it makes the trace burn. It happened to me a few times.Is it possible for the S-D bridge that a current going to it instead from may have caused the M091 to burn? A flow in the opposite direction??

author: fzabkar
author_rank: Super Contributor
timestamp: April 02, 2023, 01:48:10 am
content: I believe the keyboard and mouse ports are normally protected by picofuses or polyswitches. I guess someone could accidentally short something with a screwdriver when working one the motherboard. It's a strange one.

author: Nexxen
author_rank: Regular Contributor
timestamp: April 02, 2023, 01:57:21 am
content: I got that, otherwise what would be the purpose of a dedicated component?Ok, engineers cut corners but not this much I hope...It's just to test, if it works it works.If not it wouldn't have.I added a pic of the damaged zone. In read how the V goes around + damaged trace (not +5VSB)Time to bed. Read you tomorrow but thanks again

author: fzabkar
author_rank: Super Contributor
timestamp: April 02, 2023, 02:06:28 am
content: I haven't done much motherboard repair, so I can't help a great deal. I know that USB ports are also protected by polyswitches. You might try the people at badcaps.net. They do a lot of motherboard repairs over there. Someone may even have circuit diagrams.https://www.badcaps.net/forum/forumdisplay.php?f=14https://www.badcaps.net/forum/forumdisplay.php?f=15

author: fzabkar
author_rank: Super Contributor
timestamp: April 04, 2023, 04:00:58 am
content: Perhaps a fuse wouldn't be a good idea.That part of the circuit appears to select either the 5VSB or VCC5 supply to power the USB/PS2/LAN etc.

author: Nexxen
author_rank: Regular Contributor
timestamp: April 04, 2023, 03:36:03 pm
content: +5VSB/+5V is selcted on another trace and that actually works (on the VSB/5V pin header I have continiuty with +5VSB pin and ATX).I checked a little more and:the dead SOT23 Drain connects to another sot23 that supplies Vcc to RT8105 (https://pdf1.alldatasheet.com/datasheet-pdf/view/1131962/RICHTEK/RT8105.html).That component is responsible for BOOT and SOFTSTART.My guess is that the blown SOT23 gives Vcc necessary to turn on the m/b, without it's dead.The other two components the big mosfet connects to (red line on pics) are:-https://pdf1.alldatasheet.com/datasheet-pdf/view/21744/STMICROELECTRONICS/74ACT08.html(data I/O)-https://html.alldatasheet.com/html-pdf/218263/stmicroelectronics/st75185c/1945/1/st75185c.html(UART to SR-232)These two, if not powered, maybe just won't allow communication from serial and or other I/O on the back of the board.With a dedicated graphics card it should display something nonetheless.Thanks for all the data, it's difficult to repair something if you don't know all that is around it.Bottom line:the +5VSB actually powers the soft-on power-on of the motherboard via the SOT23.the +5V is the Gate allowing +5VSB to go to RT8105 and allow power-on ----> like a "power from ATX plugged, ready to power-on on demand"Don't know what this circuit is but I have no other explanation.

author: Nexxen
author_rank: Regular Contributor
timestamp: April 08, 2023, 12:18:09 am
content: I discovered that the other +5 to blown comp. comes from +5VSB too, but it goes through a cap and a resistor and then to the other leg (of the side that has 2 legs).Basically the blown component gets +5 to both from +5VSB.The burnt trace goes to the +5VSB/+5V 3-pin header selector. Indeed powering PS2 and USB (pin continuity with pin +5VSB from ATX)BTW: there are no dead shorts on ATX nor anywhere else. Burnt trace could have been because of +V from USB?The square component that gets Vcc from +5VSB is L6713A (https://pdf1.alldatasheet.com/datash...CS/L6713A.html)

author: Nexxen
author_rank: Regular Contributor
timestamp: April 11, 2023, 10:20:27 pm
content: I don't have a fuse, could I put a schottky diode instead? Or a resistor?If the component I found on another motherboard is compatible with this, it's just a gate + a diode.Soldering a diode between +5VSB and Drain isn't gonna be the same then?What is the value I should try, for a diode? I have a few of those.Thanks in advance!!

author: Nexxen
author_rank: Regular Contributor
timestamp: April 14, 2023, 01:15:28 am
content: Some news:- I soldered a copper wire from +5VSB to the Drain of the missing sot-23- tried to power it on but nothingIn the apst days I found some videos on YT explaining how power on works and poked around with my mulimeter.I decided to probe the crystal oscillator involved in the process of power on and it actually powered on.Keeping the probe on the + lead of the OSC makes it go full POST until boot media missing error.At this point I don't know what to do. Check the OSC?

author: Nexxen
author_rank: Regular Contributor
timestamp: April 14, 2023, 04:04:23 pm
content: The RTC OSC deosn't short.The two vias to the SB have each a Cap, one shorts to G. Once removed still have a short to G. SIgnals are ICH_RTCX2 and ICH_RTCX1Same circuit on another board R to G are 8M ohms and 3Mohms; on this board it's 7.7Mohms and 0.Board powers on at random.I'll check the 3V battery circuit.

author: Nexxen
author_rank: Regular Contributor
timestamp: April 15, 2023, 12:36:47 am
content: Issue wasn't the crystal.Something else isn't working, until I get a new sot 23 it'll be on hold.Too bad as it did boot and load linux via usb.

author: Nexxen
author_rank: Regular Contributor
timestamp: October 19, 2023, 03:49:47 pm
content: To close this case:the SB was indeed faulty, first it had the Xstal 32KHz getting a variable amount of current at different voltages.Even if it posted a few times it was a matter of time to have it dead.It did provide a good amount of spare parts that helped solve other issues on other boards.End: a lot of time wasted learning, not much learnt. Partial failure. Ok, now I feel better