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Is this a bad cap? (jenix DRO)

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  • Is this a bad cap? (jenix DRO)

    not wanting to highjack BF's DRO thread anymore I took a pick of a suspect cap, it's got very slight raising on the one end and the plastic heat shrink on the other side is all deformed... i guess i will try testing it to see if there's any connection or resistance or whatever...

  • #2
    Sounds suspicious, get the size off the label, and make a sketch showing it's polarity. Can it be replaced easily?

    Comment


    • #3
      Yes I think I can get to it if I uncouple the board, I just found a replacement cuz i save caps out of stuff - it's skinnier and longer but it's a 470uf 25 volt just like the other and has polarity on it so I think im going in...
      I will add - two other caps went bad in this head unit about 5 years ago and i replaced and totally took care of a different problem so this is kinda exciting maybe i get it going again without the glitch

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      • #4
        Keep your fingers crossed, then, AK.

        You may find this forum interesting, amongs't other things, they list the various makes and their relative quality.

        https://www.badcaps.net/forum/index....32399eb2578311
        Last edited by old mart; 02-10-2021, 01:07 PM.

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        • #5
          You can do simple checks on a cap with a ohmmeter (analogue is nicest). Dead open == infinite resistance, dead short == zero, "probably OK" == very low resistance drifting up to very high as it charges up. However, there are more subtle types of failures that won't show up this way.
          "A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979

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          • #6
            Well I gave it a good attempt --- i soldered all kinda of questionable connections too and in fact have you ever worked on boards that you wondered how they passed in the first place? this is one of them boards --- it actually looks good and organized but it's like they ran low on solder and it's a two piece that requires good connections on BOTH sides, seriously thought with all I took care of that id most likely fixed it,

            put it back together and plugged it in - the X would not register and then it finally took off --- that's when I tried the Y and it would not register and then after lots of back and forth finally started working...

            it sucks, it used to be rock solid dependable...

            Comment


            • #7
              Ok so im a glutton for punishment --- i never tested the output of the DC to mainboard --- I have of course 110 AC going into the DC transformer with only 5.08 volts coming out of it, does that seem like an odd voltage for something like this --- one of the transformer thingies says 250 v dc but im sure theres a stepdown after that right ?

              Comment


              • #8
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                I messed up in my post above it's not 250 v dc I think it's ac but it says 250 v on the board too without ac or dc should this thing have just 5 volts? anyone know ?

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                • #9
                  Don't want to appear to sound pushy or anything but did you guys know its Feb. 10th? it's annual "help an electronic hillbilly out" day... so yeah if you were holding back on the advice you really don't have to anymore because there's a special day for it and that day is today.

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                  • #10
                    I think the "250V" on that package is just a maximum rating so you don't kill the poor thing. I don't think it has any other relationship to the voltage at which it is actually being used.

                    Also, 5V (+ or minus 10% if I remember right) is a standard logic level for certain device families. 5.08 V would be in spec. The part numbers on the integrated circuit packages (U1, U2) should be a clue here.
                    Last edited by mickeyf; 02-10-2021, 06:45 PM.
                    "A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979

                    Comment


                    • #11
                      What is not said here is that those "simple checks" should be done with the capacitor disconnected from the board. This is because other parts in the circuit can easily distort any readings you get if it is still "in circuit". In some cases you can easily disconnect one of the two leads on the capacitor and that is enough to take it out of the circuit.

                      Frankly, with the symptoms described in the first post I would order new capacitors for ALL of the electrolytic ones on the board. It may take a few days for them to arrive, but just installing another used capacitor is only asking for trouble. And manufacturers usually buy all the components for a given circuit board at the same time. That means that all the capacitors on that board are probably from the same manufacturer and are roughly equally old. If one is going bad, then the others are likely to follow shortly.

                      You can easily order new capacitors that are an exact match for the ones on the board from any of a number of electronic suppliers. And their web sites make finding them easy:

                      https://www.digikey.com/

                      https://www.mouser.com/

                      https://www.newark.com/



                      Originally posted by mickeyf View Post
                      You can do simple checks on a cap with a ohmmeter (analogue is nicest). Dead open == infinite resistance, dead short == zero, "probably OK" == very low resistance drifting up to very high as it charges up. However, there are more subtle types of failures that won't show up this way.
                      Paul A.
                      SE Texas

                      And if you look REAL close at an analog signal,
                      You will find that it has discrete steps.

                      Comment


                      • #12
                        Mickey thanks allot for taking the time. oh well had to check and ask... what an annoyance when you have all systems go yet it's not all the time, does that not speak of a weak connection ? ehh i know - could be any number of things....

                        Thanks to you to Paul just read what you had to say and makes sense... I am amazed at you electronic guys, I usually can only fix obvious stuff as it all is kinda a mystery to me and easy to get lost in all the hoopla...
                        Last edited by A.K. Boomer; 02-10-2021, 06:56 PM.

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                        • #13
                          The circuit board in these photos appears to be a DC supply. I only see two connectors on it and that would probably be one for 115 VAC for the input and the other one for the DC output. 5 VDC is the most generally used supply Voltage for digital circuitry so having that at the output connector is not a surprise. In fact it is the first thing that I would expect.

                          Further evidence of this is that the parts on the board are all what I would expect for a DC supply circuit. I see a transformer, four diodes arranged side by side as it common for a full wave rectifier, some capacitors, at least one IC, and a possible inductor which could be used in a filter circuit.

                          In short, your reading of 5.08 VDC is certainly 'in spec" for most digital circuits. I have seen a lot worse. And many digital ICs specify a DC Voltage of 4.75 to 5.25 VDC.

                          It sounds to me that your DC supply is operating properly.



                          Originally posted by A.K. Boomer View Post
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                          I messed up in my post above it's not 250 v dc I think it's ac but it says 250 v on the board too without ac or dc should this thing have just 5 volts? anyone know ?
                          Paul A.
                          SE Texas

                          And if you look REAL close at an analog signal,
                          You will find that it has discrete steps.

                          Comment


                          • #14
                            If you spend years at a lathe or milling machine, then you find it easy to tell what is going wrong when making parts with them. If you spend years advising investors about investing in the market, then that becomes second nature. And if you spend years repairing electronic circuits then you also develop a skill for that. Nothing magic, just; "Been there! Done that! Didn't get the tee-shirt!"

                            The obvious stuff is easy. A charred component should probably be replaced. So should a capacitor that has it's end blown out or puffed out, getting to that point. After that it takes a Sherlock Holmes with a good knowledge of how the circuits work and what to expect at various points in them. Or, of course, you can just replace the whole assembly/circuit board. If they are available.

                            "... could be any number of things...". Yes, that is always true.

                            That 250 V on the line filter is a rating, not what should be present in this or any other particular circuit. I would expect 115 VAC on it input and output terminals, but 230 VAC is also a distinct possibility.

                            If you are talking about that black, round thing at the lower left on the circuit board, I suspect that it may be a small transformer and as Mickey said, that would only be a maximum rating for the individual component. The circuitry on that PCB also needs a DC supply to operate and that transformer may be part of the supply for that DC Voltage.

                            I still think that this DC supply circuit board is probably operating just fine. If you are still having trouble, I suspect it is somewhere else.



                            Originally posted by A.K. Boomer View Post
                            Mickey thanks allot for taking the time. oh well had to check and ask... what an annoyance when you have all systems go yet it's not all the time, does that not speak of a weak connection ? ehh i know - could be any number of things....

                            Thanks to you to Paul just read what you had to say and makes sense... I am amazed at you electronic guys, I usually can only fix obvious stuff as it all is kinda a mystery to me and easy to get lost in all the hoopla...
                            Paul A.
                            SE Texas

                            And if you look REAL close at an analog signal,
                            You will find that it has discrete steps.

                            Comment


                            • #15
                              Originally posted by A.K. Boomer View Post

                              put it back together and plugged it in - the X would not register and then it finally took off --- that's when I tried the Y and it would not register and then after lots of back and forth finally started working...
                              Did you swap scales and see if the issue is the same?

                              I just need one more tool,just one!

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