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    #1

    Soyo VT17N71

    I acquired a (2) 17" Soyo monitors to try and repair. Looks like they both have blown fuses. Picture 2 shows blown fuse, picture appears to have a blown diode on the back side (picture 3)??? It looks burnt in the corner. The other board appears to look ok. I'd like to get both working, but I may use one for parts. The input is a 12v DC external power supply which appears to be dishing out a clean 12.3 volts. Could someone point me what to look at next? I don't want to put in a new fuse and blow it without some more diagnosing.

    Thanks.

    PS. Inverter boards have fuses just after input and both fuses on both inverters are fine, so I'm thinking the problem lies in the board shown not in the inverter? Safe to assume or no?
    Attached Files
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    #2
    Re: Soyo VT17N71

    I'm not entirely which picture you mean is 1, 2, or 3. Anyway, the circled part Q502 is NOT a fuse. It's a transistor of some sort.

    The circled part F500 is a fuse.

    Step 1: Figure out what that part is that's fried. We need the writing on the top of the part. Does it look like it could be the same as the part next to it: Q503?

    Comment

      #3
      Re: Soyo VT17N71

      Yeah, my pictures did not number right..... Q502 has "S2 A" on it. Like I said I have 2 of these boards both, with blown F500 fuses. and ony the one S2 A at Q502 looks burnt. Caps all "look" good too.

      Comment

        #4
        Re: Soyo VT17N71

        That's a SMBT3906 PNP transistor. Remove it and then Check the other transistors for shorts, check ESR of caps in the area (on other side of board) if there are any.

        Then replace transistor with good part and test. This may be the same part that failed on the other board, just without visible effects of the failure.
        Last edited by el3ctroded; 06-27-2010, 11:12 AM.

        Comment

          #5
          Re: Soyo VT17N71

          Well, I can't get the burnt q502 off the board.....no matter what I do, its like its glued and soldered on. So I started on the other board....just replaced the fuse and tested the largest cap that appears to be first in line on the trace, light came on for about 10 seconds, heard a pop, fuse blown again. The cap is G-Luxon 220uf 16v. Since I don't have a cap tester. by testing it, I removed from circuit and I just verified it would take a charge with my meter set to high ohm, and it was slowly climbing. Other transistors that look like Q502 all have readings on my diode test on my meter...none appear to be shorted. Any other thoughts?

          Comment

            #6
            Re: Soyo VT17N71

            Where does the external PS plug into? P500 or PH200 on the board?

            Have you tried another PS? Say one from an universal laptop PS with changeable tips that matches the DC and amps?

            Originally posted by bsweasel
            The input is a 12v DC external power supply which appears to be dishing out a clean 12.3 volts.
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              #7
              Re: Soyo VT17N71

              P500 is power. PH200 is audio input for built-in speakers.

              I have not tried other PS... Both that I have appear to produce stable 12v power. And they power another monitor just fine.



              Originally posted by retiredcaps
              Where does the external PS plug into? P500 or PH200 on the board?

              Have you tried another PS? Say one from an universal laptop PS with changeable tips that matches the DC and amps?

              Comment

                #8
                Re: Soyo VT17N71

                To get the Q502 off: add some solder to the pin on the side that only has 1 pin. Next use a metal pick and insert it under the leg while heating the solder. Still heating the solder, pry the leg up, and pry up the part some. Repeat on the other legs.

                Some monitors use more current... I've seen a 17" require 4 amps, and a 19" require only 2. You may be causing the PSU board to fry because of too-much voltage drop on the 12v supply, which causes higher currents and can blow small parts and the fuse.

                Comment

                  #9
                  Re: Soyo VT17N71

                  removed

                  Comment

                    #10
                    Re: Soyo VT17N71

                    Great observation. Question for the OP, are these the original Soyo OEM power supplies?

                    Originally posted by el3ctroded
                    Some monitors use more current... I've seen a 17" require 4 amps, and a 19" require only 2. You may be causing the PSU board to fry because of too-much voltage drop on the 12v supply, which causes higher currents and can blow small parts and the fuse.
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                      #11
                      Re: Soyo VT17N71

                      Originally posted by retiredcaps
                      Great observation. Question for the OP, are these the original Soyo OEM power supplies?

                      Yup, original OEM power supplies. Any way to test this theory, I don't have another 12v 4amp supply other than these 2 originals.

                      Comment

                        #12
                        Re: Soyo VT17N71

                        Originally posted by bsweasel
                        I don't have another 12v 4amp supply other than these 2 originals.
                        nearly everyone has one.. sitting in their computer.. waiting to be alienated

                        Comment

                          #13
                          Re: Soyo VT17N71

                          Originally posted by el3ctroded
                          That's a SMBT3906 PNP transistor. Remove it and then Check the other transistors for shorts, check ESR of caps in the area (on other side of board) if there are any.

                          Then replace transistor with good part and test. This may be the same part that failed on the other board, just without visible effects of the failure.

                          Ok, if that is truely a SMBT3906 PNP: . I lifted pin 3 the collector and did a diode test on 1 (Base) to 3 (Emitter) and it read shorted. Base to collector gave me a reading. So I'm guessing its shorted. I've replaced it with Digikey part SMBT3906INCT-ND and replaced pico fuse with Digikey part F2315-ND. Do you think I should power on and test?

                          I'm worried I'm going to just keep blowing components and I don't have loads of this stuff to keep replacing. I just ordered a couple of each.

                          Any help would be appreciated. Thanks to all, who have chimed in, and led me so far!

                          Comment

                            #14
                            Re: Soyo VT17N71

                            Also, if I don't have a ESR meter for testing caps?

                            "you should be able to see the cap charge when you use a high ohms scale with the proper polarity - the resistance will increase until it goes to (nearly) infinity. If the capacitor is shorted, then it will never charge. If it is open, the resistance will be infinite immediately and won't change."

                            Would someone comment on this testing with a normal meter? Or is this covered in a sticky someplace?

                            Comment

                              #15
                              Re: Soyo VT17N71

                              I have 2 Benqs waiting for parts (both have blown/open fuses). Before I power on, I plan to test everything I can (without power plugged in) for shorts. While it isn't 100% accurate, you can do a lot of resistance and diode tests. If something looks suspicious, you can remove and test out of circuit.

                              Originally posted by bsweasel
                              Do you think I should power on and test?

                              I'm worried I'm going to just keep blowing components and I don't have loads of this stuff to keep replacing. I just ordered a couple of each.
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                                #16
                                Re: Soyo VT17N71

                                The test below (I think I know where it came from) won't give you an

                                1) accurate reading of the capacitance
                                2) ESR of the cap

                                For example, a 1000uF cap can "charge" as per below, but it may only be 300uF.

                                The ESR of a cap may be way too high and will affect the circuit.

                                Originally posted by bsweasel
                                Also, if I don't have a ESR meter for testing caps?

                                "you should be able to see the cap charge when you use a high ohms scale with the proper polarity - the resistance will increase until it goes to (nearly) infinity. If the capacitor is shorted, then it will never charge. If it is open, the resistance will be infinite immediately and won't change."

                                Would someone comment on this testing with a normal meter? Or is this covered in a sticky someplace?
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                                  #17
                                  Re: Soyo VT17N71

                                  Since I don't have an ESR meter, here is my latest replacements and tests. Attached is a newly marked picture. Cap with red X on top has been replaced with a used but most likely good rubycon 220uf 16v cap. I tested all the SMD resistors in the area, all seem ok. I plugged it in. The power led lights then gets dimmer. I tried the menu button and it attempts to light the CCFL's as they blink, but don't, then the power LED gets dimmer. It started smelling hot, so I unplugged it. The Large circle is the area that was VERY warm to touch after I shut it down. Can anyone help explain this? Is it that Coil labeled Sunny 4325101006? or the Diodes PJ48 SR34? Or Transistor that looks to be covered in some crusty burnt looking glue??? Any comments?

                                  PS the red arrow is the Connector that goes to the inverter board.
                                  Attached Files

                                  Comment

                                    #18
                                    Re: Soyo VT17N71

                                    Originally posted by bsweasel
                                    The Large circle is the area that was VERY warm to touch after I shut it down. Can anyone help explain this? Is it that Coil labeled Sunny 4325101006? or the Diodes PJ48 SR34? Or Transistor that looks to be covered in some crusty burnt looking glue???
                                    Check the voltage regulator too in addition to the diodes for shorts.

                                    I read, but have no first hand knowledge, that some glues over time can become conductive?
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                                      #19
                                      Re: Soyo VT17N71

                                      Originally posted by retiredcaps
                                      Check the voltage regulator too in addition to the diodes for shorts.

                                      Could you tell me which one is the voltage regulator? I'm still learning the basics of this stuff.

                                      Comment

                                        #20
                                        Re: Soyo VT17N71

                                        See yellow circled items. There may be more, but your pic isn't top down. It is slanted and hard to see.

                                        See

                                        https://www.badcaps.net/forum/showpo...13&postcount=5

                                        on how to test voltage regulators.

                                        Originally posted by bsweasel
                                        Could you tell me which one is the voltage regulator? I'm still learning the basics of this stuff.
                                        Attached Files
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