Friday, December 30, 2016

Laptop PSU power supply fix (kinda)

So I had a wonky PSU for a few weeks. It worked, kinda, but the DC cable needed to be in a constant state of twist and tension -- investigating the specifics of the fault was a low priority so I just did whatever worked, that is until today.

I remembered that in some of my past laptops there was a power fault that developed over time. The cause had been to do with a drying and deteriorating solder joint inside the laptop at the DC input. And so now in this case I firstly suspected something similar was happening, but inside the PSU.

With considerable difficulty I managed to pry open the PSU case only to find that everything inside was still quite perfect. The difference was that now I had a horribly disfigured unit that needed to be taped up.

My next hunch was to investigate was the funny looking cable segment just after the PSU DC output. And behold! I found that the negative wiring had become cut underneath the insulation. I can only speculate that at some point in the past the cable was jammed in a door or a drawer, and experienced a shearing force enough to eventually cause this fault.

The temporary fix was just to cut open some of the insulation, and twist the negative wires together. Unfortunately in the process I managed to nick some of the insulation to the positive cable, but will get by for now.

No matter how you look at this, it's not pretty. However, I was able to return back to work, and also to report back what was learned.

CONCLUSION: Don't try this. Just spend $10 to $20 on a new PSU. Even get two of them, one for home and one for the bag. Spare yourself from the waste of time.

And yes, the twisted mangled result was reasonably taped up before put back into use.

Friday, December 09, 2016

TPA3118 2X30W Bluetooth Digital Power Amplifier for Modified Bluetooth Speaker

I have this old BO speaker that's built like a tank, but what good is it when it does not connect to anything. I was going to throw it out, but had one more idea for it.

So I got this Bluetooth amp module from eBay:

TPA3118 2X30W Bluetooth Digital Power Amplifier for Modified Bluetooth Speaker
US $10.89

The DIY mod:
  1. Open the speaker enclosure
  2. Uninstall the crossover board
  3. Connect the woofer to the module's right channel output
  4. Connect the mid-range and tweeter (in parallel) to the left channel output
  5. Drill a hole for the power cable and push it through
  6. Attach the module to the inside cover of the speaker enclosure with tape
  7. Close it up

Currently the system is powered by 4x 18650 lithium battery pack that sits on the outside -- it lasts for about a day before needing a recharge). The audio signal connects via Bluetooth.

When it powers up, a voice prompt (in a Chinese accent) asks to pair, and then says that it's connected.

At minimum volume the sound can be quite hissy. The only volume control is via the source device, so I assume that the module is set to maximum preamp volume, hence the hiss. I am yet to try the 3.5mm input and test the hiss, but at low priority.

Later, I upgraded the battery holder to a single four pack, which looks a bit more tidy.

Monday, December 05, 2016