Daytek F19AH

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  • pedro
    Senior Member
    • Dec 2009
    • 199
    • AUSTRALIA

    #21
    Re: Daytek F19AH

    Originally posted by UserName666
    Wondering what the significance of 1.4 is or where it comes from?? Trying to learn something as I go here and not just play musical chairs with the components lol
    The line supply voltage is described in terms of its RMS value. The peak is 1.4 times the RMS value, and your incoming rectifier_bridge/filter_cap combo is a peak detector.

    Originally posted by UserName666
    As for the 6 pin connector it is indeed 0 volts. - lead on middle top gnd pin and + across all others 0 volts. Same with the middle bottom gnd pin. That was tested with live power. (Transformer still clicking)
    The DC at the large cap is present but no secondary voltage is derived from the SMPS. The possible candidates for this are SMPS controller, FET, SMPS transformer, output rectifier, output filter cap. The fact that the transformer is ticking suggests that the first three are still trying hard. If you get this same result with the video ("logic") board disconnected then focus your attention on the secondary rectifier(s) and filter caps.
    Friends don't let friends buy Samsung ....

    Comment

    • jetadm123
      Badcaps Legend
      • Feb 2010
      • 2169

      #22
      Re: Daytek F19AH

      Before we get too deep into this, let's get back to the 10uf cap. It is part of the startup circuit and still should be replaced. Other members have suggested that the 50V rating is used because that value is the most readily available. Try reading the voltage across the 10uf cap. If it's relatively low, for testing purposes, you might be able to use a lower voltage cap. Please observe all safety precautions, since you're working next to the high voltage cap.
      Last edited by jetadm123; 08-31-2010, 08:21 AM.

      Comment

      • UserName666
        Senior Member
        • Aug 2010
        • 76

        #23
        Re: Daytek F19AH

        If it turns out to be stuff like SMPS controller, FET, SMPS transformer, output rectifier I may have to scrap this as I have no clue how to diagnose those kind of componants.

        Upon testing that 10uf cap the 10uf 50v cap, the voltage is fluctuating between between 11 ~ 16volts.

        I will retest those Diodes out of circuit in a bit. Want to wake up a little more before I start soldering.

        For the time being does anyone have an opinion about the 11 ~ 16 voltage coming to the 10uf cap?

        Comment

        • PlainBill
          Badcaps Legend
          • Feb 2009
          • 7034
          • USA

          #24
          Re: Daytek F19AH

          Originally posted by UserName666
          If it turns out to be stuff like SMPS controller, FET, SMPS transformer, output rectifier I may have to scrap this as I have no clue how to diagnose those kind of componants.

          Upon testing that 10uf cap the 10uf 50v cap, the voltage is fluctuating between between 11 ~ 16volts.

          I will retest those Diodes out of circuit in a bit. Want to wake up a little more before I start soldering.

          For the time being does anyone have an opinion about the 11 ~ 16 voltage coming to the 10uf cap?
          That is the startup voltage. Pulsing like that indicates a problem with the SMPS (yeah, big surprise). It could be due to a bad startup cap, or a shorted diode. I'd suggest replacing the 10uF cap first. If that doesn't help, see if you can get a set of good eyes to figure out the part number of IC101. The number you posted doesn't come up on any searches.

          PlainBill
          For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

          Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

          Comment

          • Wrog
            Badcaps Veteran
            • Oct 2009
            • 472

            #25
            Re: Daytek F19AH

            Originally posted by UserName666
            If it turns out to be stuff like SMPS controller, FET, SMPS transformer, output rectifier I may have to scrap this as I have no clue how to diagnose those kind of componants.
            Don't scrap, it's the perfect opportunity to learn more. Don't worry, there are plenty of folks here that will give you instructions on what to try next. If I've read your responses correctly, you've already replaced all caps except for the big guy laying on its side, correct? What did you end up using in their place (brand, series, values, etc.)?

            Comment

            • UserName666
              Senior Member
              • Aug 2010
              • 76

              #26
              Re: Daytek F19AH

              PlainBill: The 10uf has already been replaced.
              IC101 underneath the board is:
              SG6841SZ
              KZA056005340

              Wrog: I dont know what the "series" of caps are but the brand was Radio shack. They were all originally 25v but now they are now 50v. The uf ratingings are exactly the same. Rated at 105 degrees. I don't know about the 10uf 50v cap as that was just in my parts bin but it was new. It is now 63v temp rating unknown. I'm gonna get a better/permanent 10uf once I see some action on the power LED.

              Comment

              • jetadm123
                Badcaps Legend
                • Feb 2010
                • 2169

                #27
                Re: Daytek F19AH

                Originally posted by UserName666
                PlainBill: The 10uf has already been replaced.
                IC101 underneath the board is:
                SG6841SZ
                KZA056005340

                Wrog: I dont know what the "series" of caps are but the brand was Radio shack. They were all originally 25v but now they are now 50v. The uf ratingings are exactly the same. Rated at 105 degrees. I don't know about the 10uf 50v cap as that was just in my parts bin but it was new. It is now 63v temp rating unknown. I'm gonna get a better/permanent 10uf once I see some action on the power LED.
                Most people on this site will tell you that Radio Shack caps are the wrong type of caps to use. You need low-esr caps like Panasonic FM or FC series. The "shack" caps are too general purpose and will not handle the higher frequencies the power supply operates at.

                IC101 is a PWM controller made by System General? Man, what's with all these oddball controllers made by unknown companies? Spec sheet below:
                Attached Files

                Comment

                • UserName666
                  Senior Member
                  • Aug 2010
                  • 76

                  #28
                  Re: Daytek F19AH

                  Originally posted by UserName666
                  From post #36 in the BENQ T905 post regarding diodes:
                  "Test them with your diode setting. One way should measure 0.4 to 0.7V. Reserve and the other way should measure "1" or 0L."

                  So would that mean that the diode giving me a reading of 1.643v is damaged??
                  Originally posted by pedro
                  If the diode were out of circuit then that reading would be a worry. In-circuit the reading will be affected by other componentry. Without a schematic it's hard to give a 100% guarantee but it is credible.
                  Out of circuit, no live power, DMM on diode setting:
                  Near transformer = 0 reverse .498v
                  Near filter cap = 0 reverse .493v

                  So umm I guess those are good.
                  Last edited by UserName666; 08-31-2010, 11:33 AM.

                  Comment

                  • UserName666
                    Senior Member
                    • Aug 2010
                    • 76

                    #29
                    Re: Daytek F19AH

                    OK I have been looking at that IC101 data sheet pdf for about a half hour now and am unsure where to go with it. Am I supposed to test for input voltage at the VIN pin #3 with the other lead on the ground pin #1?

                    Comment

                    • PlainBill
                      Badcaps Legend
                      • Feb 2009
                      • 7034
                      • USA

                      #30
                      Re: Daytek F19AH

                      Originally posted by UserName666
                      OK I have been looking at that IC101 data sheet pdf for about a half hour now and am unsure where to go with it. Am I supposed to test for input voltage at the VIN pin #3 with the other lead on the ground pin #1?
                      I've been looking it over and it gives some good information. Startup voltage is 15-17V, shutdown voltage is 9-11V. That handily explains the pulsing voltage on the 10 uF cap.

                      I'm going to give you the 'Cliff's Notes' version of what is happening, and speculate on what isn't happening. Refer to page 11 of the SG6841 datasheet. The part numbers I am using refer to that schematic. AC power comes in through CN1. F1 is the fuse, VZ1 is a surge suppressor, THER1 has about 30 ohms resistance at room temperature. That will drop as it warms up. The purpose is to reduce the surge as power is applied. L2 and L2, C1 and C2 are there to absorb noise transients. R1 and R2 discharge C1 and C2 so you don't get a jolt if you touch them with power off.

                      BD1 rectifies the 115 VAC in to 165 VDC. C4 is the large capacitor laying on it's side. R5 and R7 feed the start-up current to the IC. It charges C10. When the voltage across C10 reaches about 16 volts U1 pin 8 goes high and turns on Q2. This sends a burst of current through the primary of T1 (pins1,2 to pin 3). That causes corresponding pulses to appear at the secondary of T1 (pins8,9 to pins 6,7) and the tertiary winding (pin 4 to pin5). D4 feeds that pulse through R12, where it charges C9. The first thing we know is that pulse is not getting to C9 (the 10 uF capacitor we were discussing earlier). The secondary pulse goes through Q1 (a Schottky diode) and is filtered by C7, C8 and L3.

                      Regulation is handled by U2 and U3. R14 and R15 form a voltage divider. As Vo (the output voltage) rises the voltage at pin 1 of U3 also rises. When pin 1 reaches 2.5 volts U3 starts to draw current through pin 3, U2, pins 1 and 2, and R11. This turns the LED in U2 on. That causes pin 4 of U2 to pull pin 2 of U1 down, which reduces the width of the next pulse from U1, pin 8.

                      R8 is a safety feature. When Q2 turns on the voltage across R8 increases. This goes to U1, pin 6. If pin 6 goes too high, it shuts off Q2.

                      Things we know. U1 is probably good; at least it's trying to work. If you see voltage spikes on pin 8 that would more or less confirm it.
                      Q2 is not shorted. If it were, F1 would have blown. I believe you also checked the output diodes. (The transformer in your monitor probably has two secondaries, and two output diodes).

                      Things to check:

                      R8. If it's too high a resistance, Q2 shuts off early.

                      U1, pin 8. Do you see pulses there at about the same rate you saw them across the 10uF cap?

                      D4 and R12. If either are open, U1 won't get run power.

                      T1 pins 4-5. If there is no continuity, U1 won't get run power.

                      The voltage on U1, pin 2.

                      REMINDER: The component numbers are from the SG6841 schematic. You will have to translate them to your power supply.

                      PlainBill
                      For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

                      Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

                      Comment

                      • UserName666
                        Senior Member
                        • Aug 2010
                        • 76

                        #31
                        Re: Daytek F19AH

                        OK that schematic is throwing me on a real loop here. From what I can understand/find...

                        Things to check:

                        -R8. If it's too high a resistance, Q2 shuts off early.
                        ***Don't know where to look for R8

                        -U1, pin 8. Do you see pulses there at about the same rate you saw them across the 10uF cap?
                        ***Sort of. Fluctuates between .3?? - 0 - .4?? then it will fall to 0 for a few seconds then do that over again on a constant cycle.
                        Pos - pin 8
                        Neg - pin 1

                        -D4 and R12. If either are open, U1 won't get run power.
                        ***The 2 diodes on my board test as:
                        Out of circuit, no live power, DMM on diode setting:
                        Near transformer = 0 reverse leads .498v
                        Near filter cap = 0 reverse leads .493v

                        Not sure where to look for R12(PDF). I saw it going to pin 7 on the pdf so I traced back pin 7 on my board. Since the schematic shows the diode, cap and resistor near each other, is resistor R12(PDF) what I circled in Blue??
                        10uf 63v cap circled in orange
                        Diode circled in Yellow
                        Pin 7 is pink.

                        -T1 pins 4-5. If there is no continuity, U1 won't get run power.
                        ***There is continuity between both places with the red lines.

                        -The voltage on U1, pin 2.
                        ***This one is giving really jumpy readings between .035v and 1.4v

                        I also checked the voltage coming into the chip (per page 1 diagram of PDF) and its fluctuating between 15 ~ 19 volts at pin 3.
                        Neg - pin 1
                        Pos - pin 3

                        The 2nd picture is to view the board without my circle marks.
                        Attached Files
                        Last edited by UserName666; 08-31-2010, 04:42 PM.

                        Comment

                        • PlainBill
                          Badcaps Legend
                          • Feb 2009
                          • 7034
                          • USA

                          #32
                          Re: Daytek F19AH

                          Originally posted by UserName666
                          OK that schematic is throwing me on a real loop here. From what I can understand/find...
                          It's rough. This would be a lot easier if we had the schematic of the monitor.
                          Originally posted by UserName666
                          Things to check:

                          -R8. If it's too high a resistance, Q2 shuts off early.
                          ***Don't know where to look for R8
                          PDF R8 would be the green resistor standing on end on the top side of the board. It's between the blue ceramic cap at the lead end of the large cap and the heat sink for the power FET and the diode bridge.
                          Originally posted by UserName666
                          -U1, pin 8. Do you see pulses there at about the same rate you saw them across the 10uF cap?
                          ***Sort of. Fluctuates between .3?? - 0 - .4?? then it will fall to 0 for a few seconds then do that over again on a constant cycle.
                          Pos - pin 8
                          Neg - pin 1
                          Excellent. The IC is trying to drive the FET, then shutting down when Vdd drops too low. Once the 10uF cap charges up to 16 volts it tries again.
                          Originally posted by UserName666
                          -D4 and R12. If either are open, U1 won't get run power.
                          ***The 2 diodes on my board test as:
                          Out of circuit, no live power, DMM on diode setting:
                          Near transformer = 0 reverse leads .498v
                          Near filter cap = 0 reverse leads .493v
                          PDF D4 is on top of the board next to the 10uF cap. Yes, you circled it in yellow.
                          Originally posted by UserName666
                          Not sure where to look for R12(PDF). I saw it going to pin 7 on the pdf so I traced back pin 7 on my board. Since the schematic shows the diode, cap and resistor near each other, is resistor R12(PDF) what I circled in Blue??
                          10uf 63v cap circled in orange
                          Diode circled in Yellow
                          Pin 7 is pink.
                          PDF R12 is board R118. 6.8 ohms, I think.
                          Originally posted by UserName666
                          -T1 pins 4-5. If there is no continuity, U1 won't get run power.
                          ***There is continuity between both places with the red lines.
                          Good.
                          Originally posted by UserName666
                          -The voltage on U1, pin 2.
                          ***This one is giving really jumpy readings between .035v and 1.4v
                          This one is a potential 'smoking gun', subject to other readings. Internally there is a pull-up resistor to 6V (generated internally). That should be at 6 volts until the opto-isolator pulls it low. It looks like the trace from pin 2 runs under IC101, C109, R120, Z101, across the board, under J101 then to pin 4 of IC102 (the opto-isolator). What is the voltage across pins 1 and 2 of IC102?
                          Originally posted by UserName666
                          I also checked the voltage coming into the chip (per page 1 diagram of PDF) and its fluctuating between 15 ~ 19 volts at pin 3.
                          Neg - pin 1
                          Pos - pin 3
                          That makes sense.
                          Originally posted by UserName666
                          The 2nd picture is to view the board without my circle marks.
                          That is much appreciated. You've done a heck of a job. Things I've mentioned above:

                          Check R118 on the board- should be 6.8 ohms.
                          Check the voltage across pins 1 and 2 of IC102
                          Check the resistance of R8 (pdf)

                          And for something new, I'm trying to establish the link between IC101 pin 8 and the power FET (Q2 pdf). On your picture it appears the upper pin is connected to a jumper which runs across the board to a point between R109 and the orange circle. The trace then runs down to R113, and from the other side of R113 under D103. Please verify this, and identify any other connections.

                          PlainBill
                          For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

                          Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

                          Comment

                          • UserName666
                            Senior Member
                            • Aug 2010
                            • 76

                            #33
                            Re: Daytek F19AH

                            One thing I should have mentioned right of the top is this monitor was used in a poorly ventilated cabinet and all of the sudden just went out and you could faintly smell burnt electronics. The poorly ventilated cabinet makes me think this was an overheat issue.

                            Alright...
                            R118 (In circuit - no live power) = 7.0 ohms

                            Across IC102 pins 1/2 (In circuit using live power) = Fluctuations between 1.1v and 2.5v

                            R8 (Big green resistor R112 on board - out of circuit - no live power) 00.7 ohms

                            **00.7ohms????? Ive never done an LCD monitor but even to me that seem not right lol
                            Attached Files

                            Comment

                            • UserName666
                              Senior Member
                              • Aug 2010
                              • 76

                              #34
                              Re: Daytek F19AH

                              Further to my previous post (too late to edit) it looks like your right. It also looks like it connecting to the right leg of D103 too. I upped the megapixel rate on my camera and uploaded a better pic. This one is much clearer. Sorry about the blur before. Will keep my camera on this setting lol.
                              Attached Files

                              Comment

                              • jetadm123
                                Badcaps Legend
                                • Feb 2010
                                • 2169

                                #35
                                Re: Daytek F19AH

                                Great photo and fantastic job on the troubleshooting with PlainBill. Out of curiosity, just below IC101 is a a small transistor Q102. What is the marking on it? W04 something? Is it connected to IC101? If yes, can you check it for a short. Also, to the right of IC101 is C107. What happened above it? Looks as if something burned up.

                                Comment

                                • jetadm123
                                  Badcaps Legend
                                  • Feb 2010
                                  • 2169

                                  #36
                                  Re: Daytek F19AH

                                  Can you also read off the color bands on R112? Is it grey gold white orange yellow? If yes, I believe the 5th band makes it a precision resistor of 43.9 ohms
                                  Last edited by jetadm123; 08-31-2010, 08:38 PM.

                                  Comment

                                  • UserName666
                                    Senior Member
                                    • Aug 2010
                                    • 76

                                    #37
                                    Re: Daytek F19AH

                                    The marking on Q102 is "W04" then to a right angle of the it says "57". The middle leg of Q102 appears to be connected to Pin 5 or the "RT" pin of IC101. I wouldn't know how to test that for shorts.

                                    The marks are from resoldering in the 10uf 63v cap. All I have is a crappy cold heat iron right now. I have a proper 30 watt iron and proper solder sucker on order.

                                    R112 *APPEARS* to be (from top to bottom looking at the pic):
                                    Black - Gold - Silver - Orange - Yellow.

                                    Comment

                                    • PlainBill
                                      Badcaps Legend
                                      • Feb 2009
                                      • 7034
                                      • USA

                                      #38
                                      Re: Daytek F19AH

                                      That is reasonable for 'R8'. The app note says .3 ohms for their example. Your DMM probably has .2 to .4 ohms resistance in the leads.

                                      I'm getting confused here. You ARE getting voltage spikes at pins 1 and 2 of the opto-isolator so you ARE getting output of the SMPS transformer. Why didn't anything show up at the output?

                                      OK, I'm going to be looking some more tomorrow. This is FUN!!! Maybe Jetadm123 will come up with something overnight.

                                      PlainBill
                                      For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

                                      Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

                                      Comment

                                      • UserName666
                                        Senior Member
                                        • Aug 2010
                                        • 76

                                        #39
                                        Re: Daytek F19AH

                                        Assuming pin 1 of the "opto-isolator" is the little circular indent and pin 2 is directly to the right on the same side under the X then yes its between 1.1v and 2.5v.

                                        Comment

                                        • retiredcaps
                                          Badcaps Legend
                                          • Apr 2010
                                          • 9271

                                          #40
                                          Re: Daytek F19AH

                                          Originally posted by UserName666
                                          The marking on Q102 is "W04" then to a right angle of the it says "57". The middle leg of Q102 appears to be connected to Pin 5 or the "RT" pin of IC101. I wouldn't know how to test that for shorts.
                                          To test for shorts on a transistor, test the following with ohms.

                                          pin 1 to pin 2
                                          pin 1 to pin 3
                                          pin 2 to pin 3

                                          If anything reads less than 50 ohms, it suggest a possible short.
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