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    #1

    Sony MBX-197 power circuit, help me think it through

    This Sony MBX-197 comes out of an all-in-one PC. When plugged into a known and tested good power supply, a small noise from circuits can be heard while fans start and immediately stop. There is no 3.3V at the power button and no LED activity.

    I verified the fuse is good and poked around for bad solder joints and pressed on BGA chips. Checked for crossed pins in external jacks and all removeable hardware is removed and unplugged. All large capacitors verified for ESR and non-shorted.

    There is 2.25V at the USB jacks instead of the usual 5V.

    I can find +19V at various points in the power circuit. But I don't know how this circuit works.

    In the power circuit, there are two tiny identical, side by side ICs which I measured 5V at one pin and 1.1V at another.

    There are two square SC411 ICs. One has proper 5V supply, but the other does not. Datasheet is here:

    There are several 8 pin ICs with markings similar to "IOR P818M". On each of these ICs it seems that there is one voltage on one row of 4 pins and another voltage on the other row. But I don't know what these are. The non-powered SC411 is connected through a set of two of these ICs.

    Would appreciate "guru" comments, I can fix all the kinds of easy stuff, but I am not very good at figuring out complex problems in these power circuits.
    Tags: None
    #2
    Re: Sony MBX-197 power circuit, help me think it through

    Ok, I fiddled a little more with it. I was able to see 3.3VSB at the switch as well as 5V at the second SC411 briefly at startup, then they go to zero volts. Combined with the "tweet" noise, this must be an overload protection kicking in. As a bonus, one time (out of maybe 100 times unplugging/replugging the power) I was able to get the more typical repeated tweeting of an overload protection.

    I enlisted a helper to repeatedly unplug/replug the power (one tweet per replug). When doing this repeated plugging a smell as if some component let the smoke out becomes stronger. Assuming there is some shorted component triggering the overload protection, using an IR thermometer I looked for heating components. So far I only found one obviously heating component, a SMD choke marked "5R6" (Similar to ) which heats quickly to 150deg+ F with only ~5 replugs.

    So is the choke heating because it is part of the problem or because of the rapid input voltage changing? It is hard to believe a shorted choke would trigger overload, since they are low resistance components to begin with.

    Comment

      #3
      Re: Sony MBX-197 power circuit, help me think it through

      As far as suspected mosfets go (I'm not too familiar with the numbering used), I have two 4468, 4433, F7904, F8707, F8714. Other 8-pin chips nearby power circuit were eeprom, flash, etc. Any of the above part numbers usual troublemakers?
      Last edited by runderwo; 10-09-2011, 09:56 PM.

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        #4
        Re: Sony MBX-197 power circuit, help me think it through

        Maybe not overload protection after all. When power is applied, I read transient ~200V at gate driver output (pin 12) of the SC411 that remains powered. I checked gate driver voltage input of that SC411 and there is no spike there. This driver output would drive the MOSFETS that power the second SC411. Seems to be overvoltage shutdown, but gate driver output is the cause or effect?

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          #5
          Re: Sony MBX-197 power circuit, help me think it through

          Did anyone ever find a solution to your problem. I am having the exact same problem but I do not know about voltages or what is wrong but I have the exact symptoms. Is it repairable of is my motherboard toast?

          Thanks

          Comment

            #6
            Re: Sony MBX-197 power circuit, help me think it through

            Usually this kind of thing is repairable if you can just find the problem and if components are not discontinued. I have not found the problem yet but I am tempted to throw some mosfets at it.

            Comment

              #7
              Re: Sony MBX-197 power circuit, help me think it through

              I found the MOSFET 4433 ( ) only reads 99K ohm from source to gate and has 19V present at both source and gate with a near zero voltage at drain. Something is wrong here. I will desolder this suspect and test it out of circuit.

              Comment

                #8
                Re: Sony MBX-197 power circuit, help me think it through

                4433 had 50 ohms S->G and D->G when unsoldered. Replaced with new (measured Mohms S->G, D->G) and there is no longer the "tweet" when power is applied. Still 19V at gate and 0V at drain. Moving on...

                Comment

                  #9
                  Re: Sony MBX-197 power circuit, help me think it through

                  Got back to this tonight.
                  Found bad AO D452 n-channel FET. <10 ohms gate/source/drain all directions. There are a total of 3 of these fets on the board, I will replace all of them.

                  Datasheet here:


                  Replacement component is D452A but so far I can't find for purchase.

                  Fairchild FDD6796A seems like suitable replacement.


                  Somehow spilled flux pen contents all over myself.
                  Last edited by runderwo; 11-20-2011, 09:48 PM.

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                    #10
                    Re: Sony MBX-197 power circuit, help me think it through

                    Hi Runderwo, I have a MBX-197 (MB813MP Rev. 1.2) from a Sony Vaio All-In-One with power issues too. Bought the complete computer unit at an auction only to find it didn't come on. I found the same as you the two ADO452A's were blown and the 5R6 (5.6uH) SMD choke was fried. I had to replace the 5R6 (Rewind with 3 x strands of ECCW-0.25 aka SWG-33, 7.5 turns anti-clock wise) after frying the two brand new ADOs i had just replaced. After doing this and another set of ADOs, SHE NOW COMES ON!!! Seems it does cut out some noise that otherwise interferes with the dc to dc and HT generation causing these other circuits to draw excessive current. Replace/Repair this coil (nail varnish remover gets rid of the lacquer, and clear nail varnish works wonders to glue it all back together)

                    The only issue I have now is that both CPU fans are 4 wire and NOT the conventional pin out, In BIOS both show as 0RPM, and she runs of hours, in normal operation however a critical failure is displayed before booting and it shuts her down after 10 seconds.

                    P.S. i can give you a link to who i got my ADO FETs from if you are still looking. (if you are in RSA i can give you some cause i had to buy 10 so i got spare)

                    Comment

                      #11
                      Re: Sony MBX-197 power circuit, help me think it through

                      Apologies: To clarify the CPU fan problem. I have tested the fans with a scope and all signals are correct on another MB. On the MBX-197 both fans turn on and run full tilt after 3 seconds of applying power and the VAIO logo displays on the LCD. (indicating the PWM line and 5v supply is working on the main board) but somewhere on the tachometer line or the corresponding sensor IC(s) something is either being pulled down or is open circuit. (haven't found it/them yet, still tracing down the IC)

                      This causes the RPM to be reported as zero and thus the MB repeatedly shuts down to prevent over heating and states that there are no fans detected as the critical failure under normal operation.

                      If you remain in the HW monitor where it shows the 0RPM you can leave it there for hours and nothing over heats, dies or fries. The heat sinks for GPU & CPU and even the heat pipes them selves remain cold to the touch. If fans are disconnected however, in 10 mins you risk burning your fingertips. So there is a definite temp change when in this scenario not just that it is sitting at low RPM state.

                      If you get this far or further with your board please let me know.

                      Comment

                        #12
                        Re: Sony MBX-197 power circuit, help me think it through

                        Your model uses M814 motherboard, I can find the schematic but it's on a Russian forum that requires you to register and post 15 times before you're able to download.

                        I found the M810 which is probably close enough for your purposes? You can see on page 36 and 18 the fan tachometer signals all go to inputs directly on the ICH10 chipset.

                        Curiously enough either the schematic is incomplete or there is no embedded controller/keyboard and mouse controller/superIO on this system?
                        Attached Files

                        Comment

                          #13
                          Re: Sony MBX-197 power circuit, help me think it through

                          You guys are great. I gave up on the motherboard because I could not determine the source of a short near the southbridge and, due to burned looking southbridge chip and zero ohms after removing all nearby SMD components, assumed southbridge was shorted. I could not spend any more time on it. With the schematic I probably would have had more luck finding the problem but I had to give up on it due to time constraints. Thanks for participating and hopefully this thread will help the next guy. This seems to be a very common problem with this unit since I bought a replacement motherboard for the unit on Ebay and it was dead in the same way (sent it back for refund).

                          Comment

                            #14
                            Re: Sony MBX-197 power circuit, help me think it through

                            Originally posted by Devler32 View Post
                            Hi Runderwo, I have a MBX-197 (MB813MP Rev. 1.2) from a Sony Vaio All-In-One with power issues too. Bought the complete computer unit at an auction only to find it didn't come on. I found the same as you the two ADO452A's were blown and the 5R6 (5.6uH) SMD choke was fried. I had to replace the 5R6 (Rewind with 3 x strands of ECCW-0.25 aka SWG-33, 7.5 turns anti-clock wise) after frying the two brand new ADOs i had just replaced. After doing this and another set of ADOs, SHE NOW COMES ON!!! Seems it does cut out some noise that otherwise interferes with the dc to dc and HT generation causing these other circuits to draw excessive current. Replace/Repair this coil (nail varnish remover gets rid of the lacquer, and clear nail varnish works wonders to glue it all back together)

                            The only issue I have now is that both CPU fans are 4 wire and NOT the conventional pin out, In BIOS both show as 0RPM, and she runs of hours, in normal operation however a critical failure is displayed before booting and it shuts her down after 10 seconds.

                            P.S. i can give you a link to who i got my ADO FETs from if you are still looking. (if you are in RSA i can give you some cause i had to buy 10 so i got spare)
                            can someone please help me fix my motherboard please? the motherboard is powering on fans are spins but its not displaying anything on the screen! i have reflowed the video card several times with no luck at all! if you can push me in the right direction that would be great!

                            Comment

                              #15
                              Re: Sony MBX-197 power circuit, help me think it through

                              Maybe vga chip is shorted and you should do a reball instead of reflow

                              Comment

                                #16
                                Re: Sony MBX-197 power circuit, help me think it through

                                Originally posted by pctek View Post
                                Maybe vga chip is shorted and you should do a reball instead of reflow
                                i have a spare board here that need a new 5R6 if anyone can point me in the right direction for that that would be awesome thanks

                                Comment

                                  #17
                                  Re: Sony MBX-197 power circuit, help me think it through

                                  I've got the same issue. Devler32 did you ever manage to sort out?

                                  Comment

                                    #18
                                    Re: Sony MBX-197 power circuit, help me think it through

                                    Sorry to bring back a thread from so long ago, but I just wanted to report a successful repair. I had a similar issue, no power and a momentary buzz/squeal noise when power was connected. I replaced the 5R6 with a unit from Digikey(linked below). And am happy to report that the unit powers on and works great now. Thanks to everyone for the information in this thread. I would not have been able to figure this out on my own.

                                    http://www.digikey.com/scripts/DkSea...70053280049134

                                    Comment

                                      #19
                                      Re: Sony MBX-197 power circuit, help me think it through

                                      Hi friends, got same problem solved with repacement of coil 5R6

                                      Comment

                                        #20
                                        Re: Sony MBX-197 power circuit, help me think it through

                                        Hi i know this is an old thread but just to add my finds with the same unit, i bought 1 of ebay after trying to power it i got the quite beeps dead power and shiver of the fans, i read this thread and ordered a 5r6 from ebay and now the machine powers but the fans report as 0rpm in the bios and only if i press f1 instead of f2 can the computer boot as normal, the fans remain at full tilt/speed and i have tested everything and installed different windows from vista to windows 8 all working perfectly has anybody got any information on solving the fan issue please?

                                        Comment

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