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    Need assistance -- Video Game CRT Color Monitor

    Hi Forum,
    I can certainly use some help.
    I was kindly offered an upright arcade video game "Street Fighter" with a 19" color CRT monitor with a name brand "Yatta". I have reached out to many arcade parts houses and with the search in Google, I cannot find anyone that is familiar or have heard of this brand so I would like to reach out to all of you.
    First, I need to locate a set of schematics of the unit – Second I am in need to locate a Flyback Transformer BSC23-F1412A
    I started to troubleshoot the monitor and found that the 2A fuse was open (Note: Someone added an external wire instead of the fuse across the terminals) – I started to do more troubleshooting and located the following bad parts;
    1) Shorted - Main NPN Power switching transistor for the flyback
    2) Open – Power Resistor 8 Ohms Attached to the Emitter leg (Current Limiter)
    3) Shorted - A series pass NPN Power transistor
    I went around thoroughly with my ohm meter and started to probe all the resistors, transistors, capacitors and diodes on the board to see if there are any other parts that have fatigued – Conclusion is no other parts to me seem to have died however if there is a “Walk and Wounded” part – that may be.
    I located and purchased all the parts (Except for the flyback) and replaced them all including the fuse – after applying 110VAC power I heard a faint arcing noise and the repeat of the 2A fuse open. I went straight to the resistor and it was still measuring 8 Ohms. I checked the 2 previously shorted transistors and found they were still measuring good. I suspect the flyback at this point. What is interesting is that the high voltage retained a charge in the CRT Picture tube since I discharged that path – I heard it. Perhaps an inner winding (High Voltage Breakdown) problem in the flyback.
    Here is where it gets tricky and this is where I turn to the community for help. – Hopefully I haven't lost anyone yet –
    The flyback is getting tougher to locate since the phasing out of CRT's – You still can locate flybacks from China and Ebay but they are getting scarce by the minute. The one particular part that I need I cannot locate – I am on a mission to substitute with an equivalent part – I am strictly challenging myself to see if this can be achieved – No other reason.
    The PC board backside doesn't help me much since it doesn't include silk screening with descriptions which means I went strictly on trace to trace from part to part to give me an approximate destination and output.
    I have attached pictures to help with my story and quest. Any help is greatly appreciated – If I have left something out please tell me so I may provide it.
    Thank You,
    Richard
    Attached Files

    #2
    Re: Need assistance -- Video Game CRT Color Monitor

    I would try and check what the B+ voltage is going to the horz. output transistor, If the B+ regulator circuit is bad it could be giving too much voltage to the horz. circuit. The voltage is usually around 120 volts, If the regulator is bad you could be getting 160 volts to that circuit and there would/could be arcing due to too much high voltage

    Any other names or numbers on the pc board? What are the numbers on the transistors you replaced?
    Last edited by R_J; 08-14-2017, 08:49 PM.

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      #3
      Re: Need assistance -- Video Game CRT Color Monitor

      This might be close?
      Attached Files

      Comment


        #4
        Re: Need assistance -- Video Game CRT Color Monitor

        Hi RJ --
        I believe you are so very close to the actual schematic of the unit -- How did you know just by my description? Amazing -- thank you..
        What I noticed on the chassis is a marking with Model 700 -- Nothing more than that.
        The transistors I replaced were --
        Main Switching HV Transistor - Philips BU2520DF NPN Power Transistor SOT199 800V 10A
        Regulator Series Pass Transistor - 2SC5071 Silicon NPN High Speed, High Voltage
        Regarding the schematic I notice the flyback illustrates pin configuration to 12 - I only count 10 plus I don't see a pin 1 on the schematic. Pin 1 when I trace the back side it connects to the collector of the Main Switching Transistor. Pins 7 & 8 are tied together via a trace and it connects to the collector of the series pass transistor.
        I am drawing up a diagram of the flyback winding -- Just by a quick measurements with a DMM
        1-2-10 appear to be common winding
        3 -4- 5- 6- 8 appear to be common when measuring out of the circuit inner winding.. 7 has no inner connection to anything beside possibly being common to the secondary side.
        Thank you for the reply and schematic..
        Last edited by richajem; 08-14-2017, 11:35 PM.

        Comment


          #5
          Re: Need assistance -- Video Game CRT Color Monitor

          They usually count all the pins, even the missing ones, on your flyback pins 11 and 9 (or 2 and 4 depending on how they number it) are not there but if counted you would get 12
          In that schematic Q903 collector should be connected to ground (line missing in schematic)
          This looks like it may have been one of those China replacement chassis. not the original that was in the game

          The schematic came from arcade-museum.com
          Last edited by R_J; 08-15-2017, 11:46 AM.

          Comment


            #6
            Re: Need assistance -- Video Game CRT Color Monitor

            yes, sounds like one of the "universal" replacement chassis.

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              #7
              Re: Need assistance -- Video Game CRT Color Monitor

              RJ --
              Today I was studying the schematic especially the Power Stage Q903 and was scratching my head with how in the heck can the regulator operate with the 2 collectors going to no where. I am more familiar with series pass transistor circuits when the collector is ties to the unregulated side and the emitter is the output regulated side - I will study it more with the grounding of the collector.
              I am not quite following your flyback approach - Can you please elaborate a bit more?
              Also, How would you approach the checking of the B+ circuit when I need to power up the winding or were you thinking to test the Q903 Regulator circuit for a bad reference voltage to the flyback 120V, would this be in open circuit?
              Last edited by richajem; 08-15-2017, 10:04 PM.

              Comment


                #8
                Re: Need assistance -- Video Game CRT Color Monitor

                I had this in post #5
                In that schematic Q903 collector should be connected to ground (line missing in schematic) I checked another diagram that had it corrected

                You unsolder the B+ line going to the flyback transformer or remove the horz. output transistor and measure the voltage from the regulator. It should be regulated even without a load
                The flyback/horz. circuit does not need to operate for this. The regulator ciruit regulates the B+ which controls the amount of high voltage, too much B+ and there will be too much high voltage which could start arcing.
                Last edited by R_J; 08-15-2017, 10:23 PM.

                Comment


                  #9
                  Re: Need assistance -- Video Game CRT Color Monitor

                  Hi RJ --
                  I understand the Q903 wiring error on the schematic – I made that change according to your Post 5. Thank You again..
                  What I was asking pertains to your brief description in post 5 in regards to the Flyback diagram and Pin assignments -
                  You wrote -- They usually count all the pins, even the missing ones, on your flyback pins 11 and 9 (or 2 and 4 depending on how they number it) are not there but if counted you would get 12
                  I just wanted to see if you can provide me with additional information (More than you have described) to what you were stating because I am not familiar to the approach you listed.
                  Regarding the Flyback - There are only 10 solder pins on the underside of the flyback and you had mentioned it can be a count to 12. I was just wondering how is that possible and how do they conventionally tailor those assignments? Looking at other transformer layouts I just see the typical clockwise counting pin to pin.
                  OK -- I can do that check with the B+ verification to see where its voltage currently regulates too.
                  Thank you again –
                  Richard

                  Comment


                    #10
                    Re: Need assistance -- Video Game CRT Color Monitor

                    I just remember some boards numbered them that way (ask me 20 years ago) I can't find an example so go with the way you were counting them, one and two being the primary winding as they like to keep a distance between those pins
                    sometimes they will number all the spots (holes) on the pc board but have one not used. that unused pin can be missing on the flyback, so if you counted the pins on the flyback itself and skipped over the missing pin the numbering would not match the board. Its no big deal, I just remember seeing it
                    Attached Files
                    Last edited by R_J; 08-16-2017, 03:26 PM.

                    Comment


                      #11
                      Re: Need assistance -- Video Game CRT Color Monitor

                      remove the drive transistor, or isolate the transformer.
                      then connect a 60w 220-240v lamp across B+
                      it should light and be stable.

                      Comment


                        #12
                        Re: Need assistance -- Video Game CRT Color Monitor

                        Thanks RJ and Stj --
                        That will be my weekend test -- Currently I have the flyback removed so I can test it easily. I will add a light bulb as a load.
                        I uploaded a few photos of the top side and bottom side.
                        Attached Files

                        Comment


                          #13
                          Re: Need assistance -- Video Game CRT Color Monitor

                          btw, if you know any OLD tv repair shops/guys - ask them if they have a "ringer"
                          it's a device for testing line-output transformers for internal shorts.
                          i wish i could find mine right now, i have a monitor to fix myself.

                          Comment


                            #14
                            Re: Need assistance -- Video Game CRT Color Monitor

                            just a thought - what is the original monitor?
                            anything on the tube or framework?

                            foto's?

                            because an original chassis would be better than these cheap crappy retro-fit's
                            the original stuff lasts decades!

                            Comment


                              #15
                              Re: Need assistance -- Video Game CRT Color Monitor

                              Hey Guys,
                              I had to take an extended period of time away from troubleshooting this monitor to attend family matters -- I am here and i have some new discoveries -- Please read --
                              So I went back to the forum to refresh myself --
                              Hi RJ and stj -- I can still use your help!
                              So I pulled out my meter and started to probe the power supply section (regulator transistors Q903/Q902/Q901) and found that Q901 was open - So after replacing Q901 with a comparable equivalent i powered up the chassis without the flyback and loaded with a light bulb and found the B+ voltage to be 161V solid - Now with that said i seen that RJ that you mentioned in a post earlier that it is possible that the B+ is high causing the arcing and that is the train affect of the short propagation. It appears that it is high - I was wondering what is the proper voltage for B+? Poking around in other color monitor schematics and user guides and i read that the B+ is adjusted between 100V - 200V - But reading that i figured 160V may suit this board but I am not sure, what do you guys recommend?
                              I didn't try to move the pot VR901 to see if the voltage varies - I will try that next with reinstalling the bulb as a load -- but what should i shoot for a target to adjust B+ too?
                              Prior to that -- I was thinking that the voltage appears to be regulating normally https://www.badcaps.net/forum/images...blow.gif(+161V) after replacing Q901 and let me reconnect the flyback - I powered it up and I heard and felt the high voltage static on the screen for about 10 seconds and then the 2A fuse opened - went back to check the Q901 an it was fine and I went to check the Q903 and that also seemed fine and what took out the 2A fuse was Q302 - HV transistor BU2520DF - The internal body resistor of 50 Ohms was shorted across the Base and Emitter. Prior to that discovery I replaced the 2A fuse and started to troubleshoot the circuit - I still had the +161V regulation voltage and knew i had no more HV as I was trying to check the lower voltage taps off the flybacks - By the way, I did not find a replacement flyback nor had the flyback checked for the health other than just verifying the taps and inner winding shorts.
                              But the 2A fuse was not clearing with the HV xsistor shorted internal resistor which was discovered afterwards but during that time I was looking for voltages to where they should be like the IC Vcc and so on -
                              And here I am --
                              STJ - There are no markings on the original monitor -- It appears that there were any when I got the monitor - The only markings exist are the ones off the chassis - But like you said in a prior post - they swapped out the original with this replacement board - I posted photos of that in the original post -
                              Your advise is welcomed please --
                              Thank You, Richard
                              Last edited by richajem; 02-24-2018, 11:26 AM.

                              Comment


                                #16
                                Re: Need assistance -- Video Game CRT Color Monitor

                                Here is an Update --
                                After replacing Q902 with an equivalent, I noticed the voltage was still in the upper range of 161V +/-3V at which it tells me it still was not regulating.
                                I visually checked the traces and noticed the silk screen on the bottom and top appear incorrect with the actual trace and reference to the schematic. The Base and Collector markings are reversed. After kludging the Q902 leads around to match the schematic and the traces, I powered up the Power Supply section only and the voltage was in the order of 154V with a 7W light bulb load. I replaced the 7W load with a 60W load (Light Bulb) and the voltage dropped to 140V. Now with turning the pot VR901 for fine tuning the 140V, the voltage was changing but not grossly. 140V vs 165V is a big difference when you stack up the turns ratio and output voltage on the High Voltage side.
                                But I am not sure what is the magic voltage number, can someone help with that ?
                                Also what other checks do i need to do before going for smoke test by including the Main Switching HV transistor? I am guessing the HV short on that side took out the regulator circuit. Do I need to go for a 100W bulb test and see what the voltage will yield? Are there scope waveforms to collect such as the HV driver circuit?
                                I tried to look everywhere for a flyback and I can't find the original piece - perhaps an equivalent - Does anyone know how I can obtain that?
                                remember -- When I power up for the initial short period, there is high voltage as i felt it and had to discharge it at the tube with a ground rod so it does attempt to power up but something takes out the Main Drive Transistor -- Q302.
                                Food for thought -- Has anyone questioned the semiconductors being sold on the market for possible silk screen replacements and authenticity? I have heard of this at work for space application parts being sold as parts screened for higher reliability but are found to be commercial grade. Any take on that?
                                Richard

                                Comment


                                  #17
                                  Re: Need assistance -- Video Game CRT Color Monitor

                                  Another Update --- Any Assistance is appreciated --
                                  I did attempt to power up the board again after adjusting the B+ Voltage to 112V. I did place a 60W bulb as a load and swapped out the 60W to a 100W to be sure the load current difference would regulate the bus. And sure enough that delta was about 0.3V difference. I was impressed!
                                  Next I "placed" the Main switching HV Transistor and once again the High Voltage started up as I hear the static charge but shortly after the 2A Fuse cleared and this time the HV Transistor shorted and this time it took out the Regulation Transistor - Q903.
                                  I am suspecting the Flyback now as being the problem. What do you think fellas? Any ideas or suggestions? I am at a road block here..

                                  STJ - There are no original markings when I got the CRT Monitor - It is a 20" and Heavy than *%$#. I guess my other thought to this is that I cannot find the original Flyback (See my first post for the part number) and I feel more comfortable with what I have now and I wonder if you guys recommend that I find a substitute and cut the traces and jumper the wires across to the designated areas?

                                  Thanks,
                                  Richard
                                  Last edited by richajem; 03-16-2018, 04:43 PM.

                                  Comment


                                    #18
                                    Re: Need assistance -- Video Game CRT Color Monitor

                                    Folks,
                                    Here are some pictures of the bottom board with my figures to the flyback pinouts along with other back side and top side pictures--
                                    Any support is appreciated.

                                    Thanks,
                                    Richard
                                    Attached Files

                                    Comment

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