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What are these things?

Discussion in 'General Electronics Discussion' started by gillang, Feb 20, 2014.

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  1. gillang

    gillang

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    Thanks! Sure looks like it. What's the point to have all those letter/number code written on the board if in no way does it identify the part?
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    They don't want you to figure it out.

    The manufacturer knows, and that's the way they like it.
     
  3. gillang

    gillang

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    Feb 20, 2014
    Early in the thread, Jpanhalt did write:
    You might find a similar looking ("color" and physical size) one nearby and measure it.
    So,what's the difference between a black or a beige ceramic capacitor?
    He also wrote: I would then remove the component (E16 ) and test it. If you have a capacitance meter, use that. Otherwise, just use a DVM to see if it is shorted.
    Isn't it what I did using a test light?
     
    Last edited: Mar 1, 2014
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    I'm not sure. What was the capacitance you measured?

    How does it compare to another similar component?
     
  5. gillang

    gillang

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    Feb 20, 2014
    I didn't measure anything. All I had was a test light made of a 1.5 volts battery and a LED light. A ceramic capacitor that is short means that from one side to the other, no electricity passes...right?
    There's no other component that looks like this one. Or they are bigger or they are not the same color( beige instead of black).
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    No, a short means that current passes through it.

    A capacitor is normally open, no current can pass.
     
  7. gillang

    gillang

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    Feb 20, 2014
    Jpanhalt wrote: (on page 3) I suspect the start switch is logic-driven, like the one on your desktop. It has been awhile since the start switch was directly on/off for the power supply on such electronic equipment.
    If you load the guitar with 4 good batteries and there's no voltage at the wire that comes out of the motherboard to feed the on/off switch...does this mean the problem is right there at the very beginning of the whole start-up process?
     
  8. gillang

    gillang

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    Feb 20, 2014
    How works a logic driven switch?

    [Moderator's note: This post, and the following 7 posts, were in a separate thread in the Electronics Repair forum called "How works a logic driven switch?". They relate to the same MIDI guitar as this thread, so I merged the two threads on 2014-03-06. -- KrisBlueNZ]

    If the unit is battery powered(6 volts) should one expect to have some 6 volts somewhere at the switch...all the time...some time...not at all?
     
    Last edited by a moderator: Mar 5, 2014
  9. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    You need to give a lot more information. I don't know what you're asking. You have a "logic driven switch" that's powered from a 6V battery?

    Can you tell us the make and model number of the thing you have, a description of it, and perhaps upload a photo?

    To upload pictures, click Go Advanced then click the paper clip icon.
     
  10. gillang

    gillang

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    Feb 20, 2014
    Here are the pictures:
    switch1 shows the switch from the top.
    [​IMG]
    Switch2 shows the switch from the bottom.
    [​IMG]
    switch3 shows the identified different parts from both the top and bottom view.
    [​IMG]
    switch4 shows what is connected together when the switch is "off" and when it's "on".
    [​IMG]
    In no way is the 6 volts from the battery ever reaching the switch directly. It goes directly to the 4 wires connector, then to the motherboard and then(I guess) comes back to the switch. So,my question is...should I have a 6 volts reading at the wire that comes back from the motherboard ? Also, this is a MIDI guitar and you won't find any information about it.
     
    Last edited: Mar 4, 2014
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    On the appropriate pins, yes.
     
  12. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Here's what I can tell you from looking at those pictures. I think you've probably figured it out already.

    The device you've marked "thermistor or ceramic cap" is probably a PTC thermistor - I can see the tops of the letters "PTC" just to the right of it in the first photo. It's probably a "Polyswitch" or similar - a resettable fuse that protects the circuit against excessive current by getting hot and going open circuit. When the overload is removed, it cools down and reconnects the circuit. So it's called a "resettable fuse".

    The four-pin connector JP2 seems to carry the positive supply voltages. (But not the 0V rail!) The BAT+ wire (positive from the battery, I guess) connects to pin 2. Pin 3 connects a supply voltage into the switch and it comes out on the middle pins of the switch, and goes out on pin 4. Pin 1 comes from the centre contact of the 4.5V DC connector position. When the switch is OFF, the resistor (brown-black-red I think - 1 kilohm) connects pin 4 of JP2 to the 0V rail, to kill the circuit.

    Edit: To clarify, I think the pins on JP2 are:

    1 = positive supply, before ON/OFF switch, from centre pin of 4.5V DC socket (not fitted), going to motherboard.
    2 = positive supply, before ON/OFF switch, from red wire from battery, going to motherboard.
    3 = positive supply, before ON/OFF switch, coming back from the motherboard, going to the ON/OFF switch.
    4 = positive supply, after ON/OFF switch, going to motherboard.

    The negative wire from the battery, and the outer contact from the 4.5V DC connector position, connect through the PTC (see above) to the 0V rail of the circuit board, which connects to three pins of the MIDI socket (probably unused), and possibly to the 0V connection on the micro USB connector, but apparently not to anything else. I would expect to see a connection from that rail to the motherboard. Do you know where this is? I don't think it's on pins 1, 2 or 3 of JP3; I think these come from the micro USB connector.

    Pins 4 and 5 of JP3 are probably the MIDI data output from the motherboard; this is a current loop signal that feeds an optocoupler at the other end. I assume this unit only generates MIDI and does not receive it.

    Pins 6 and 7 of JP3 connect to the two brown wires. What do these connect to?

    So your red and green dots just show what connects to what, right? They don't show whether voltage is present t those points or not?

    Yes, if that switch is an ON/OFF switch, I would expect positive battery voltage (fed to the motherboard on JP2 pin 2 or pin 1) to come back from the motherboard on pin 3. If you have voltage on pin 2 (from the battery red wire) (which presumably feeds into the motherboard) but no voltage on pin 3, I would say there's a break in the circuit at the motherboard.

    It's possible that this break is deliberate; obviously, there is SOMETHING connected between those points at the motherboard end, otherwise there would be no need for those two wires. (Even if pin 2 was used as an "always ON" supply to back up some stored parameters, which is possible, there would be no need for pin 3, unless there is some kind of interrupting circuit between pin 2 and pin 3.)

    Is there a switch on the motherboard to select between battery power and power from a power supply plugged into the adapter socket? If that's set wrong, you'll get continuity between JP2 pins 1 and 3, but not from 2 to 3, and the unit won't receive power.

    Can you post photos of both sides of the motherboard in the area around where the wire from JP2 plugs into it?
     
    Last edited: Mar 5, 2014
  13. gillang

    gillang

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    Feb 20, 2014
    Thanks! You wrote:
    The negative wire from the battery, and the outer contact from the 4.5V DC connector position, connect through the PTC (see above) to the 0V rail of the circuit board, which connects to three pins of the MIDI socket (probably unused), and possibly to the 0V connection on the micro USB connector, but apparently not to anything else. I would expect to see a connection from that rail to the motherboard. Do you know where this is? Well...I don't know what is the OV rail???
    You wrote: So your red and green dots just show what connects to what, right? They don't show whether voltage is present t those points or not? You're right. I will do a test this afternoon to see if there's voltage at pins 3 and 4 with the switch off and on.
    There's no switch to alternate from or the 4 X 1.5 volts battery or the USB socket that provides 5 volts. The 2 brown wires, just beside the red bar + and the black bat -,are going to a very small press button switch that you have to press while starting the guitar to fix a non-starting guitar by re-uploading the firmware using a recovery tool(which in my case,didn't work).
    I did start this new thread because the one I had already going (5 pages long) went dead(nobody would answer anymore) so there's tons of photos there...maybe you could see from them where the wires from JP2 connect to the motherboard. I'm not home now so I can't use a photo editor to indicate you where they connect to the motherboard. Will be able to do so only later in the day. Here is the link to that other thread.
    https://www.electronicspoint.com/these-things-t267413.html
    There's only one connector that has 4 pins so I'm about sure the other end of JP2 that connects to the motherboard is in that picture just below the part I did circle in yellow.
    https://www.electronicspoint.com/these-things-t267413p2.html
     
    Last edited: Mar 5, 2014
  14. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    OK, thanks for the link to the other thread. [The threads are now merged into one.]

    It's really not clear what has happened to the board and the components inside the red circle in the second picture in post #12 in the other thread. Can you clean that area using firm pressure on a cotton swab and isopropyl alcohol, to remove all the crud that's making it hard to see properly, wait for it to dry, and take another photo of that area.

    Does the four-wire lead from JP2 on the board in these posts connect to the connector marked JP2 in the first picture in post #12 on the motherboard?

    If so, check the four components next to that connector on the motherboard. From left to right, they are:
    1. Small inductor marked L7 - measure continuity or resistance from end to end - it should measure short circuit (continuity test should beep) or less than 2 ohms.
    2. Unidentified diode, marking SJ with a line across the end furthest from the connector. Test it from end to end, using the diode test range on the multimeter. With the black probe to the end with the line, you should measure between 0.2V and 0.7V. With the red probe to the end with the line, you should measure open circuit (as if the probes are not connected to anything).
    3. Small inductor labelled L6. Measure as for L7.
    4. Diode labelled D2. Measure as for the other diode.

    If either of the inductors measures open circuit (or more than a few ohms), you can try soldering a thin wire across it. But there may be something else damaged on the board, so that may not be a good idea.

    Also, can you measure resistance with the red probe on pin 4 of the JP2 connector on the motherboard (that's at the right end, nearest to D2) and the black probe on the 0V rail of the board, which you can find on the round pad of the component position marked C38, just left of the yellow circle on the first picture in post #12 on the other thread. Let us know what resistance you measure.

    Edit:

    When you've cleaned up the board, take a photo looking directly down on it, and two more photos looking at a slight angle. So we have three photos looking down on it at three angles: \|/

    When you've replied, I will merge this thread onto that one.
     
    Last edited: Mar 5, 2014
  15. gillang

    gillang

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    Feb 20, 2014
    I just did the test and I got 6 volts at pin 2 and 3 all the time and also at pin 4 when the switch is "on" so...no luck,the problem isn't there. I had made the clean up last week and removed the E16. I did test it and it's not short. You did ask for 3 pictures but... the lens is at less than an inch from the board to take those close-up pictures so unless you're square to it, you get almost noting in focus since the debt of field is so small. With an angle shot, you get about 3/16 of an inch of debt of field which is about just good to see E16 in focus. It may not show in the pictures but that damn E16 is barely longer than 1/8 of an inch. Here is the straight top view again.
    [​IMG]
    You did suggest to measure a few things. Sadly, I don't have such an instrument.
    Here is the whole story of what I think did happen. I sent the guitar for repair in mid November. First, I guess they did try their firmware recovery tool (which I did many times to no avail). Then, they did open it up,disconnected all the connectors and removed the 4 screws that hold down the motherboard, Next, they un-soldered the battery ground so they could get the motherboard out of the way. They did replace my motherboard with a new one( or at least with one they knew was working) and they fired it up and it went "on" right away. They then did contact me to tell me it would cost $60. to fix it(replacing the motherboard). I then told them to send it back to me without fixing it. I think they then look at my motherboard closely and did decide to try to save it by re-soldering some spots where the solder was looking the worst(like E16). The top of the motherboard doesn't look so bad but on the bottom, many solders look bad...like porous.
    The only thing that I ever thought could be a hint as to where the problem is that... when you switch "on" the guitar powered by the batteries, nothing happen. It's completely dead. But, when you power it via the USB cable. you get a flashing red button so that means that some part of it is working until it reaches a certain spot...that I have no clue where it is. Thanks for your help.
     
    Last edited: Mar 5, 2014
  16. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    You've done a good job cleaning up the board. None of the components in that picture look damaged at all. You might want to clean up the other areas that you marked in the other photos, and re-photograph them.

    I don't think there's anything wrong with the small board with the switch and MIDI connector on it. But I'm not sure how the 0V ("zero volts") on that board connects to the motherboard. There should be a wire - I think it must be on JP3, the 7-wire connector - that connects the 0V rail on the small board - that's the large copper area that connects to the mounting tags of the switch and to three pins on the MIDI connector - to the 0V rail on the motherboard, which is the large copper filled areas on both sides of the board. The 0V rail is also called GND or ground. It's the common reference voltage point for the whole thing.

    If you don't have a multimeter, you're going to have a lot of trouble diagnosing the problem with the unit. It doesn't seem to be very well made. I'm not sure that it's worth repairing.
     
  17. gillang

    gillang

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    Feb 20, 2014
    At one point you did talk about the 0V rail (among many other things). In my reply, I did tell you I didn't know what the 0V rail was but you didn't answer that question so I couldn't answer any question about that even though you did ask. Now, with your last post, I know what the 0V rail is so here is where it connects from the switch board to the motherboard, Both area are circled in red.
    [​IMG]
    [​IMG]
    You can see that the switch board end of the ground wire is part of the things they did re-solder and they didn't clean it up(well...in the picture we don't so much that there's a lot of flux around that point).
     
    Last edited: Mar 6, 2014
  18. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Right. Yes, I didn't explain it before, sorry. So that wire is connected at both ends, and the thing still doesn't work?

    As I said, you'll need at least a multimeter if you want to go any further with it.
     
  19. gillang

    gillang

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    Feb 20, 2014
    Yep, the wire is connected and it doesn't work. Might come back here later if I ever decide to buy a multimeter.Thanks again!
     
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