1.5 Repair Attempt, Working but CPU / 3v3 Regulator getting hot

Hi There,

Wondering if anyone could advise, I killed my 1.5 board somehow (probably short) Which resulted in a MCU which had a dead short across the power pins and a dead regulator.

I was able to get a replacement MCU (at scalper prices mind you) and reworked it onto the board.
The Regulator, I was able to find an equivalent but its so tiny I found it too hard to solder - in the end I used an AMS1117 bodged onto the output of D61 and the GND/3.3v out bodged across C62.

The board is now fully working though I am concerned as The current draw seems off, and both the new Regulator and MCU are getting rather hot.

I’ve noticed that upon poweron, the whole system draws around 110ma peak while the boot sound is playing.
It will then drop to ~20ma while idle.

When you then ignite the saber, and the hum is playing etc, the current draw jumps up to 500-600ma. It doesnt feel right to me. Seems a lot considering theres no power leds / strip connected at this point. Wonder could the FETs be involved but they shouldnt be drawing anything if they arent hooked up?

Possibly the heat killed the orignial regulator as I remember when it stopped working it being really hot. The original MCU Im sure I killed futzing around.

Appreciate any thoughts or suggestions

These things are tricky.
First of all, the MCU should not be getting hot, that means there is a problem somewhere. If you’re lucky, that problem is a short outside the MCU somewhere where it can be fixed. If you’re unlucky, it’s inside the MCU…

For most standard config files (no touch buttons, no display) the CPU should draw less than one mA when idle.

The draw when it’s playing sound is much higher.

The draw when USB connected is also higher, but the power is then drawn from the usb cable, so if you measure current drawn from the battery, it should be nearly nonexistant. (At least until you start playing sounds.)

Generally, if the CPU is running at full speed, but no sound is playing, the board should draw something just under 40mA if I remember correctly.

Are you using hot-air or an iron?

Hey thanks for replying - I have both hot air and Iron at my disposal. Even with the hot air I was struggling getting that tiny part aligned and on the pads. Figured I could hot wire something easier to solder to do the same job and I had a drawer full of 1117’s

Since, I realised I wasnt completely honest - I had the Fet grnds and Fet led wires still connected to the battery even though I thought there was no current path, I need to check wiring there. Something weird was going on. Anyway with those all disconnected the draw looked a lot happier about 200ma peak while everything running (no leds).

Got one of those laser temp readers today so Ill do some more checking my side

Hope you have more luck than I did with that.
My laser temp meter was just not accurate enough, and then it died.
Been thinking of buying a thermal camera, but I haven’t had enough reason for it yet.

I got a SEEK thermal that plugs into the phone. It’s meant for distance though. Helps find cold leaking into the house or a deer or a sniper in your yard. Haven’t actually tried it on a PCB.

Yeah, I would need one that can focus at ~6 inches or closer.

Just following up on this. Actually I did find the cheap IR sensor useful - indeed it has bad focus but I found that you can move around the board and spot the general area of hotter devices and figure it out. Obvs not a pinch on a FLIR or something like that.

Eventually figured out the problem was blown FETs - the Gate and source seems to be shorted on these when they die so it was just running current through the MCU via the 3.3v regulator and getting hot. Nearly all the FETs had perished. I have replaced them all with a lower spec FET with the same footprint and the board is working again.

Do you get many snipers?

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