Love the Mega Menorah 9000! ... but might have overheated mine?

Does anyone have any suggestions about what's a reasonable length of time that the MM9000 should be able to be plugged in and running without overheating the components? I'm wondering if I might have connected something wrong, because the other night I had been running mine for about 15 minutes when it suddenly stopped working. When that happened, the 4-pin Color button felt very hot to the touch, but all other components were still perfectly cool. Do button switches have a a correct orientation that they're supposed to go into the board? I didn't think they did, but it's worth checking! I'm wondering if I killed that button with excess heat. Is that possible?

Now when I plug in the menorah after that event, the LEDs go on and I get power to the board, but the LEDs aren't being controlled by the programmed chip, it seems, because they're just doing their own thing and going on and off and choosing colors at random without responding to the Color and Night buttons. I can see from the schematic that the Color button is connected through R1 to one of the chip pins, so I'm guessing that if I burnt out the Color button, that would probably break the circuitry that controls the LEDs? (Is there a way I can test with a multimeter to find out if the button is dead, or if it's something more serious like the chip being dead?)

Thanks for any advice you can give me, and thanks to Evil Mad Scientist for making this great kit! I loved putting it together!


Comments

  • The Mega Menorah 9000 should be able to be stay on indefinitely. 

    If something got hot, that sounds like something was genuinely amiss, and there are a few different things that might have gone wrong. 

    The buttons do have a specific orientation, but (1) they slip in easily the correct way and can only be forced in the wrong way through protracted wrangling that involves weird bending of the pins (2) they can't sit flat against the board if they're in the wrong orientation. Even if you did manage to get them in the wrong way, that alone would make the button nonfunctional, but it should not overheat or cause other trouble; the switch is protected by R1, which limits the current through the switch to a very modest 5 mA.  Similarly, a short circuit within the switch should only be able to cause a maximum of 5 mA current. And, 5 mA at 5 V should limit that to 25 mW of power, which is not enough to get "very hot" on a component of that size.

    My best guess is that there was (possibly, is still) at least one short circuit on the board. With power disconnected, use your multimeter to check all four pins of the switch, to see how it is connected. Test first on the other switch ("Night"), to see what a (likely) good switch should look like. Two of the pins on one side are electrically connected, as are the two pins on the opposite side. Then, when you press the button, all four pins should be connected together.

    Check to see if the two buttons respond this way. Also, check to see if they appear to be connected as per the schematic. S2 should connect to Vcc with a button press, S1 should connect to GND with a button press. Also, and importantly, check that these lines are not connected to other lines that they shouldn't be. Also check, for example, that neighboring pins of the IC are not connected, and that the ends of nearby components such as R1 and R2, are not connected.

    Please let me know what you find.

  • Great debugging suggestions! The connectivity behavior of both buttons is exactly like you described, so now I'm convinced that those switches are both fine. The multimeter shows continuity between a couple of adjacent pairs on the IC, so that must be my problem! There are no solder bridges that I can see, so I'm betting that there must be a bridge or two hiding under the chip on the top side of the board...I do tend to feed the solder so that the blobs go through the top side, so there's probably a short hiding up there somewhere. :)

    I also measured the resistor values for the heck of it (they were all correct when I started the kit, but I wanted to see if any of them changed when the circuit overheated), and R6 is only around 10 ohms or so... definitely nowhere near 1.5k. I have a few spare 1.5k resistors lying around from a past project, so I'll try swapping one in for R6 when I go in to fix the joints on the IC. I hope to report back with good news when I'm done with those fixes!
  • Interesting. I'd suggest check the resistor color code on R6 to see if is the right type of resistor (1.5 k should be brown, orange, red, gold), and try measuring with your ohmmeter both ways across that resistor _after_ you fix the issue with the shorted pins.
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