Blown amplifier?

so managed to do a bit more work towards finding the culprit and had some disappointing results.

while I was at it I upgraded to OS 5.9 just to see if that would work by itself, but alas that did not do the trick.

next I reduced the volume in my config to 1500 and again no joy.

I did as you suggested @ForceMantle and replaced the swingh, swingl and swing files to see if that would work. (I swapped them out each file one by one and then all of them together)
i even swapped the hum file to see if that would help.
now I swapped them with a font I know works even at low voltage from the battery and I’m still getting some distortion.
it is a bit less than what I was getting from the TFA GRAFLEX font.

so I’m totally confused now.

could this maybe have something to do with my config setup?
its just plain weird that this is the only blade/font on my config to be suffering from this.

I did have a look at the sound files in audacity and all the swing files are just under the 0dB limit, and I think this is normal from my recollection.

@profezzorn, the 5v external supply, could this be done by plugging in a usb while the board is on?
would this supply the 5v needed to check the switch mode for operation?

I’m afraid not. The amplifier does not draw power from USB.

It’s possible that the font config has something to do with it, but then why would it only happen when the battery is low?

ok I will look at getting something in for this then.

I did wonder this too but I’m kind of just throwing stuff at the wall and seeing what sticks.

I think I will try a new config and blade style and see what results I get from that.

so I took the font files that seem to be causing the issue, swngh, swngl and swng and ran them through audacity normalising them to -6dB and put them on the SD card.

this seems to have done the trick… only a slight bit of distortion but only on the odd occasion.

not sure if this was the genuine cause or if this was just a wok around (I’m guessing the latter) but it seems to be working much better now.

could it be that as multiple tracks were playing that the amp is being stressed?

I think it was mentioned above that running a large speaker would stress the amp so am wondering if running the 8ohm version might be better for this size of speaker?

Any good progress with this yet?

Not yet, got to get a power supply to test the 5v step up supply.

But for the moment the -6dB reduce wav files are working OK.
Not a total cure but its works much better than it did.

Might be a while as I’m saving for holiday.

But ill will post when I get it tested and go from there.

Check your DM’s.

Finally got hold of a regulated power supply off my dad and found the time to test the board.

soldered some rather long wires to the +5v pad and GND so I could swing the saber.
first test. full battery… worked as expected.
second test. half battery… as expected, the strange over drive / distortion can be heard.
third test, psu turned on… problem solved! it works flawlessly!

thank you to all that have helped me (@profezzorn , @NoSloppy , @ForceMantle ) problem solve this.
@profezzorn proffezzorn you were right!

now the next question is, is this and easy fix and how do go about it?

That’s great, because now we know that the problem is in the booster circuit.
This is the entirety of the boster circuit:

Most likely, the problem is U3, which is a TPS61230DRCR

That part seems to be difficult, but not impossible to find right now.
Octopart says you can find it here:

Or, you could lift it off another board.

Now, soldering QFN components basically requires a hot-air soldering station, but those can be picked up for less than $50 and can be used for lots of things. You may also need some soldering paste. Usually it’s best to clean off some of the existing solder and replace with fresh solder paste when doing SMT soldering.

Now, it could be one of the other components in the booster circuit that has a problem. Like maybe Q7, L1, some of the capacitors or the voltage divider created by R2 and RN5 (not shown in the diagram), but from the description, I would think that U3 is the most likely culprit.

Not sure if this qualifies as an “easy” fix or not…

If this all seems to complicated, you could always just bridge the 5V and BATT+ pads. You will loose some volume by doing this, but the sound will function properly.


thank you for the help and advice (complete with schematic and explanation)

I will look on acquiring the relevant items as I’m sure I will use them in other areas.

if I bridge the 5v and batt + I assume this will not do any lasting harm and is therefore reversible?
was thinking of doing this while I wait for the parts to arrive.

It’s possible that the booster will work harder to try to raise the voltage that way. It’s usually only done when the booster is completely busted, so I don’t really know if it will cause any problems.

Generally, the easy to tell if if there is a problem is to check for heat. If nothing gets heat, it’s probably fine.

ok I will give it a try and see if it gets hot.
either way I will have parts on order very soon to replace the booster.
thanx again for the support.