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Author Topic: SOLVED: Nano Biscotte v4: Random LED glow and speaker pops when untouched.  (Read 592 times)

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Offline Moxized

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Hi all. I've journeyed into bringing life into a gutted 2010 Master Replica's Vader hilt I got stupid cheap.

Everything went smoothly, modified the switch into a tactile button, setup a tri-cree dark-red/dark-red/white to a CSS adapter. used 1.2ohm 3watt on the red. .5ohm 3watt on the white.

Wires braided down to a Nano Biscotte V4. with a 28mm speaker, powered by a trustfire 3.7 li-on.

Table test went great, fired up and responded well, until the 1.2ohm smoked and popped. Decided to give each red it's own resistor instead, makes no sense to me but, well that's what it is now, and no burnouts since.

It has been fine the past few days, never left on for more than a couple minutes at a time, no dueling, just simple taps for testing and programming the settings.

This is when I noticed the the White LED was staying on, but dim, even when not being activated. I also noticed random pops from the speaker. When selecting a bank, the LED seems to fluctuate to the speaker's sound.

I took it apart and checked continuity with my meter, Switch is fine, LED wiring is fine, so I checked the board, I found that with the switch and LEDS disconnected, if I touch from the positive battery post to one of the negative LED post, it would spike, then level back out.

I used a soft brush and circuit cleaner to brush the board clean. but no change.

So I did the only reasonable idea, I stuck it in my oven at 420F for 5 minutes and then allowed to cool to room temp.

I soldered all the wires back on and put things back together and it seemed to fix it, I had no issues at all, until today, it started the same thing again, only this time one of the red LEDs randomly flickering and speaker popping while left on the mantel.

So the battery is back out as I sit scratching my head. Is it likely I just have a bad board?

Seems I cannot share images even the built in attachment in the post tools gives that same error.
« Last Edit: June 25, 2019, 10:42:43 PM by Moxized »

Offline erv

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1.5 or 1.2 ohm per red die leads indeed to 1A per die (single resistor in initial wiring lead to more watt in a single res, hence smoke).

did the problem happen after charging your saber ? if so, what charger do you have. It's possible that the driver needs service, but in general that little flickering indicates that the soldering to the led has a small ground path somewhere.
(not sure the baking was a good idea)

pictures would be helpful, you can host them on various sites dedicated for this purpose, starting with google.

Offline Moxized

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Thanks for the reply!

I think it is because my account is fresh that posting images won't work I tried my google album, and attaching through the post attachment, both ways pops up in red that it's not allowed.

I'll try it again.

As for the board in the oven, don't worry, I wasn't planning warranty or repairs, likely will buy another if it comes to it haha! I've reflowed multiple boards in the past, figured what the heck, and it did seem to correct the issue for a few days at least.

And for the battery I opted for removable 3.7 cells to use on a wall charger instead of a charge port built in.


Offline erv

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the board looks just fine to me, solder job as well. Since you seem tech savvy, you might want to give a try to replace the driver from your red dice (the small 3 leg transistor near L-) and replace with a Si2302, just in case it got an issue. It cheap enough and quick enough to be worth a try, in the case your first resistor setup overheated the driver.

Offline Moxized

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I like this idea!

I placed an order and will update what happens. You weren't kidding about cheap, and the fewest I could order at least gives me 50 chances haha.

The resistor popping makes sense to me now, the two reds were over demanding of it.

Thanks again!

Offline Moxized

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Erv, you're magnificent!

The pieces arrived yesterday and I quickly replaced the chip out before we lost power at 9pm.

Fired up without issues, and no random speaker pops or glowing from the LEDs anymore when turned off and left on the table.

Picture isn't the best, but I'm very happy this new display piece is complete. Thank you!

Offline erv

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very happy to hear you got it fixed ! and congrats for swapping the tiny SMD yourself

Offline Moxized

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Haha, yeah SMDs are fun, we've been acquainted since I began using them in lighting of scale models. Suffering is attaching hair thin enameled wire to a 0402 LED. But, with dental binocular loupes, trusty hakko iron, and a shot or few to steady the hands. I can get it done.

Offline Moxized

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Well it was a short lived victory.

I woke up today and saw the blade glowing red on my shelf. I tried the switch but nothing happens, swapped the battery with a fresh charged one and the same thing happens, red dim glow with no action from the switch. I pulled the board and checked all my solder connections but nothing is lose.

Seems overnight something must have shorted. The board is dead I think.

I still want to give a big thanks for the help and ideas. I think it's best I just buy another board at this point.

I've attached a few pictures for anyone with interest, these pictures are after the Si2302 replacement.

« Last Edit: June 11, 2019, 01:20:42 PM by Moxized »

Offline erv

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try outside of the hilt / rewire with a simple setup (switch and light, no sound)
hard to tell what has died if it has without knowing what caused the short (if any)

Offline Moxized

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Youtube video of the test:
Biscottefail - YouTube

I went ahead and gave it a try. with only the battery, LEDs and switch connected there is no activity, I do see when I insert a battery there is a flash from one of the red LEDs.

Pressing the switch, nothing happens.

I removed the board all together and just connected the LEDs between the switch and battery itself. Pressing the switch lights up the Red and white LEDs, but I noticed one of the red LEDs is not lighting up, So one of the resistors must have failed again. I'm pretty sure I used the correct setup for a dark red LED, I use a 1.2ohm 3w resistor to each of the red LEDs.

Deep Red Cree Part# XPEEPR-L1-0000-00C01
425 Radiant Flux @ 350mA
Forward Voltage @1000mA = 2.5v

I'm left scratching my head.

« Last Edit: June 12, 2019, 12:52:11 AM by Moxized »

Offline Moxized

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So just an update to this I think I might know what lead to at least part of the issue.

I based my resistors off the calculator on TCSS website, it suggested the 1.2ohm 3W they sell

My own manual calculation I got 1.2 Watts. It seems the store only sells 1.2ohm in 3 wattage so it was rounding up and why it suggested that.

While the resistance is the same I think the larger resistor was generating more heat, especially combined in a group with the positive wire connecting to all three resistors before they split off to each LED. I think this is why I had wires melting and resistors popping.

I am instead going to use 1.2ohm 2W 1% resistors to each Red LED, and this time skip a resistor to the White LED since it is only used for flash on clash. I'm also wondering if it would make any difference or sense to put one resistor on the positive of one red LED, and another resistor to the negative of the 2nd red LED. The Tri-Cree is wired in parallel. My reason to do this would be to separate the resistors with at least some space instead of being up against one another. as these are LED it shouldn't matter if the Resistor is on the Pos or Neg legs. If this idea is stupid, please let me know haha.

I have resistors and a new NBv4 on the way. I'll post more on the rebuild once parts arrive.

Offline erv

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resistors have no polarity along the current path, so they can be placed on the positive or negative side of the LED.
Resistors are important in any case. Check the resistor bargain section of the manual, if a resistor calculation leads to very small R value, use the drive to adjust the current in your led (skipping the resistor).
Also, the only real accurate way to determine your led Vf is to use a bench power supply, then run the calculation for the resistor. The Vf from the datasheet is just a ballkpark.

Offline Moxized

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Another update, the new board is installed outside the hilt and already acting wonky. I set the FDrive to 870 while leaving the Drive at 1023 since I have no resistor to the white FOC LED

Left sitting outside the hilt it will randomly trigger the sound font boot sound with a flash from the white LED. then sleeps.

I'm starting to think it may be the LED heatsync itself, I noticed the heat has exposed back more wire and its close to the edge of the copper of the heatsyncs. I'm not sure if there is any contact happening but it's the only idea I have that could cause some kind of short.

Tomorrow after work I'll resolder the wires to the LED board, and this time brush down some liquid electrical tape to help prevent any rubbing/contact of the wires to the copper edges.

Offline jbkuma

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It looks like the leads on you LED could be shorting on the base.