Announcement

Collapse
No announcement yet.

JVC RX-6042 5 secs then shuts off

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    #21
    Re: JVC RX-6042 5 secs then shuts off

    i found a open darlington pair on one of the amp boards and these pieces i cant get locally. i have had to order them from ebay so ill be a week before ill post again. i dont know if i have damaged something because now after i pulled out that amp board and tried to power up i am blowing the 8amp fuse on the board labeled LVA10209-C9.it is a fuse located right where the mains enters its even before the liniear transformer. im not overly concerned about this because i am suspecting it has to do with the missing board but i thought it was worth a mention in case i should check something else while i am waiting for parts

    and R1355 is NOT open and flowing in one way only

    Comment


      #22
      Re: JVC RX-6042 5 secs then shuts off

      Removing a board is not likely to blow a fuse (by itself), more likely the amp was repetitively powered with a shorted condition which kept putting thermal stress on the fuse until it blew, OR the damaged part has simply gotten worse.

      Something recommended by some who build and repair AC mains powered gear is to use a current limiter during testing. It can be something as simple as a 60W incandescent light bulb wired in series on the AC hot lead, people build test jigs on a board with a power cord, light bulb, and an AC outlet to more easily put it in series with the gear being tested by not having to alter the gear's AC power circuit itself.

      Comment


        #23
        Re: JVC RX-6042 5 secs then shuts off

        i didnt think that removing the board made any sense to my new fuse problem.

        your first hypothosis is invalidated due to the fact i melted 3 fuses in 3 mins after the first failed.

        the lightbulb idea is great, low tech, adjustable, easily diagnosed, effective. ill dig around for a light bulb socket

        as for now is there anything else i can check to stop this from happening?

        Comment


          #24
          Re: JVC RX-6042 5 secs then shuts off

          after many trails i am back and think i am close to getting this thing figured out. my fuse problem was the output case touching on the heatsink, i did not realize the case was connected to one of the legs. i have found 2 sets of darlington pairs shorted and have replaced them only to have one fail right away afterwards. on the third install it went up in a blaze of glory with flames and everything. although this wasent good it pointed with a big arrow to where i suspect my problem is.

          sandwiched in between the 2 outputs there is a collection of....

          3 resistors.
          R330 -470 ohm
          R326 -360 ohm
          R328 - 470 ohm

          1 thermistor (i think)
          Q310 - 2SD637/QR

          1 transistor (i think)

          TH302 - QAD0012-202

          i can get the radio to come on and play sounds it is just when i try to move the volume up and down that it explodes.

          R330 is the worst failure it actually melted right into the board.

          i have 5 individual amp boards and my question is if something is failed/failing should i order 5 parts and replace on all 5 amps?

          also with these failed parts, are they the failure? or a side effect of something else that has failed?
          Attached Files

          Comment


            #25
            Re: JVC RX-6042 5 secs then shuts off

            One thing you should do to help you from blowing up new transistors, hook up 75~100 watts bulbs in series with you amplifier, that way if something shorted out the lamp will lifgt up real bright and limit the voltage to your amp. I used thsi setup for 35 years and saved a lot of new fuses and new transistors.
            to burn up the 470 Ohms resistor which is part of the Bias circuits (including the transistor) it must have shorted path for a lot of cuurent. You should monitor the bias current of the out put transistor by measure the DC voltage on the 0.22 Ohm resistor, typical class AB bias should be around 20~25mA (no input signal), so @25mA flowing through 0.22 Ohm, you should have about 5mV DC across the emitter resistor. Also check the DC offset, it should be in mV range. Pot VR302 is for the bias current adjustment. The service manual should tell you how much it should be.
            Never stop learning
            Basic LCD TV and Monitor troubleshooting guides.
            http://www.badcaps.net/forum/showthr...956#post305956

            Voltage Regulator (LDO) testing:
            http://www.badcaps.net/forum/showthr...999#post300999

            Inverter testing using old CFL:
            http://www.badcaps.net/forum/showthr...er+testing+cfl

            Tear down pictures : Hit the ">" Show Albums and stories" on the left side
            http://s807.photobucket.com/user/budm/library/

            TV Factory reset codes listing:
            http://www.badcaps.net/forum/showthread.php?t=24809

            Comment


              #26
              Re: JVC RX-6042 5 secs then shuts off

              i put the lightbulb between the actual 110v plug and the wall outlet?

              i tried looking up a bias circuit online and most of it was well over my head, is it possible to explain the function of this circuit without getting too technical?

              what should i do next? order and replaced burnt parts? what i am GUESSING has happened is the transistor at loc q310 has shorted causeing everything else to fail around it. can someone confirm or deny this theroy please.

              if my idea is true should i replace all the Q310's in all 5 amps?

              i cant find anything about what the trim pot should be set to all i can find is that it is a 1k pot this one is measuring at 300 ohms and the amp board next to it is measuring at 330

              Comment


                #27
                Re: JVC RX-6042 5 secs then shuts off

                Originally posted by scampo77 View Post
                after many trails i am back and think i am close to getting this thing figured out. my fuse problem was the output case touching on the heatsink, i did not realize the case was connected to one of the legs. i have found 2 sets of darlington pairs shorted and have replaced them only to have one fail right away afterwards. on the third install it went up in a blaze of glory with flames and everything. although this wasent good it pointed with a big arrow to where i suspect my problem is.

                sandwiched in between the 2 outputs there is a collection of....

                3 resistors.
                R330 -470 ohm
                R326 -360 ohm
                R328 - 470 ohm

                1 thermistor (i think)
                Q310 - 2SD637/QR

                1 transistor (i think)

                TH302 - QAD0012-202

                i can get the radio to come on and play sounds it is just when i try to move the volume up and down that it explodes.

                R330 is the worst failure it actually melted right into the board.

                i have 5 individual amp boards and my question is if something is failed/failing should i order 5 parts and replace on all 5 amps?

                also with these failed parts, are they the failure? or a side effect of something else that has failed?
                Seems like an overvoltage on the resistors, which is causing them to blow.

                Check Q308, Q310, and D304 for shorts.

                -Ben
                Muh-soggy-knee

                Comment


                  #28
                  Re: JVC RX-6042 5 secs then shuts off

                  Q308, Q304 both tested fine. but Q310 is the one that had melted down and blew off the board.

                  i need to know before i order these parts if this is likely a local problem or if these transistors (or anything else) fail as a team. should i replace Q310,Q810,Q909,Q809,Q309? there is one of these transistors on each amp, also 4x thermistors.

                  the outer legs measure 330 ohms and the rest are all <100k ohms on the remaining 4 amp boards. and all 4 thermistors measure 830 ohms

                  when i order parts usually the parts are cheap but they kill you on S+H

                  Comment


                    #29
                    Re: JVC RX-6042 5 secs then shuts off

                    Originally posted by scampo77 View Post
                    Q308, Q304 both tested fine. but Q310 is the one that had melted down and blew off the board.

                    i need to know before i order these parts if this is likely a local problem or if these transistors (or anything else) fail as a team. should i replace Q310,Q810,Q909,Q809,Q309? there is one of these transistors on each amp, also 4x thermistors.

                    the outer legs measure 330 ohms and the rest are all <100k ohms on the remaining 4 amp boards. and all 4 thermistors measure 830 ohms

                    when i order parts usually the parts are cheap but they kill you on S+H
                    Hm, something must have made the resistors burn,
                    check the output transistors, Q316 and Q318.

                    If Q310 shorted then the voltage across all the resistors (the ones that blew) would drop, and they wouldn't have blown.
                    They burn because of overvoltage, the more voltage applied across a resistor, the more current it will draw, and hence the more power it will dissipate as heat. If it dissipates enough energy it will catch fire.

                    And yes, in amplifiers like this there are cascade failures

                    -Ben
                    Muh-soggy-knee

                    Comment


                      #30
                      Re: JVC RX-6042 5 secs then shuts off

                      Do you have clearer diagrams, it will be easier to explain how it works?
                      Never stop learning
                      Basic LCD TV and Monitor troubleshooting guides.
                      http://www.badcaps.net/forum/showthr...956#post305956

                      Voltage Regulator (LDO) testing:
                      http://www.badcaps.net/forum/showthr...999#post300999

                      Inverter testing using old CFL:
                      http://www.badcaps.net/forum/showthr...er+testing+cfl

                      Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                      http://s807.photobucket.com/user/budm/library/

                      TV Factory reset codes listing:
                      http://www.badcaps.net/forum/showthread.php?t=24809

                      Comment


                        #31
                        Re: JVC RX-6042 5 secs then shuts off

                        This is what I use to put the lamp in series with the Hot (Line) side of the load (the equipment you are repairing).
                        http://s807.photobucket.com/albums/yy352/budm/Tools/
                        Attached Files
                        Never stop learning
                        Basic LCD TV and Monitor troubleshooting guides.
                        http://www.badcaps.net/forum/showthr...956#post305956

                        Voltage Regulator (LDO) testing:
                        http://www.badcaps.net/forum/showthr...999#post300999

                        Inverter testing using old CFL:
                        http://www.badcaps.net/forum/showthr...er+testing+cfl

                        Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                        http://s807.photobucket.com/user/budm/library/

                        TV Factory reset codes listing:
                        http://www.badcaps.net/forum/showthread.php?t=24809

                        Comment


                          #32
                          Re: JVC RX-6042 5 secs then shuts off

                          If you look on one of the first pages of this thread you will see all the pdf docs I am working with. There is a parts list, schematic, and owners manual. You can zoom in and print screen and open in mspaint so you can draw all over it.

                          And my ouptputs are not shorted.

                          Comment


                            #33
                            Re: JVC RX-6042 5 secs then shuts off

                            Originally posted by scampo77 View Post
                            If you look on one of the first pages of this thread you will see all the pdf docs I am working with. There is a parts list, schematic, and owners manual. You can zoom in and print screen and open in mspaint so you can draw all over it.

                            And my ouptputs are not shorted.
                            ok, can you check Q314, Q312, and D306, D308?

                            -Ben
                            Muh-soggy-knee

                            Comment


                              #34
                              Re: JVC RX-6042 5 secs then shuts off

                              they seem fine the lowest reading i can get is on Q312/4 i am getting 73 ohm on the outer legs. they both measure the same

                              Comment


                                #35
                                Re: JVC RX-6042 5 secs then shuts off

                                should i order 1x 2sd637 and 1x QAD0012-202 ?

                                Comment


                                  #36
                                  Re: JVC RX-6042 5 secs then shuts off

                                  Originally posted by scampo77 View Post
                                  they seem fine the lowest reading i can get is on Q312/4 i am getting 73 ohm on the outer legs. they both measure the same
                                  Hm, did you read the resistance of them in-circuit? If you did then they should be ok; the resistance you measured was from R338 and R342 in parallel.

                                  Try taking Q302 out, if it is open circuit then that is the problem. If it is not the problem, then I don't know what else could be broken.
                                  Muh-soggy-knee

                                  Comment


                                    #37
                                    Re: JVC RX-6042 5 secs then shuts off

                                    i finally found time to mock up a led circuit for this transistor 10k ohm to the base 470 ohm + led on the collector and ground on the emitter and i put a switch in there and i can turn the light on and off.

                                    i think i should order these parts, is there anything else i should replace along with the transistor, 3 resistors and thermistor?

                                    Comment


                                      #38
                                      Re: JVC RX-6042 5 secs then shuts off

                                      i have ordered my parts but i am still very curious about the lightbulb inline thing. i dont quite understand how to wire it. i made a picture is one of them correct?
                                      Attached Files

                                      Comment


                                        #39
                                        Re: JVC RX-6042 5 secs then shuts off

                                        Inline = in series

                                        You want the bulb in series with the PSU, so you want to use diagram B.

                                        Diagram A shows the bulb in parallel with the PSU.



                                        I think this method is typically done with a standard tungsten-filament incandescent bulb.

                                        In either case, I suggest you have a look at: http://www.repairfaq.org/sam/smpsfaq.htm#smpstslbt
                                        "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
                                        -David VanHorn

                                        Comment


                                          #40
                                          Re: JVC RX-6042 5 secs then shuts off

                                          I use incandescent bulb, the wattage is depended on how big the amp I work on, normally, 100w bulb is good enough for moat work, that is why I made the box so I can easily change the bulb.
                                          Never stop learning
                                          Basic LCD TV and Monitor troubleshooting guides.
                                          http://www.badcaps.net/forum/showthr...956#post305956

                                          Voltage Regulator (LDO) testing:
                                          http://www.badcaps.net/forum/showthr...999#post300999

                                          Inverter testing using old CFL:
                                          http://www.badcaps.net/forum/showthr...er+testing+cfl

                                          Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                                          http://s807.photobucket.com/user/budm/library/

                                          TV Factory reset codes listing:
                                          http://www.badcaps.net/forum/showthread.php?t=24809

                                          Comment

                                          Working...
                                          X