Repairing a Neewer 660 Studio light - How Hard Can It Be? -- Episode 594

Yes, PWM to the LED driver circuits for each colour of LEDs. I had checked the lights independently and they are working fine, it's just the control that's dead, I think I may have ended up cutting that section of testing from the video, at one point it was an hour long fault finding episode!
I tend to have both colours set to approx 50%, so wouldn't be that hard to wire up as fixed. Great suggestion, as I hadn't thought about that as a possibility, but it very rare that I change them.

Not yet, life has been busy! I have some plans in my head though, for when I get to it :) Currently thinking 555 based control (well 556, theres 2 PWMs to be controlled independently).

For some reason I honestly hadn't thought back to the fact I've got an identical unit, by that point it was mounted back above my desk!
But trying to obtain the code off it is an interesting solution, although I suspect it might be read protected (I know all the products I've worked on in the past we have protected the microcontroller code).

As far as I can tell the micro takes the potentiometer inputs and outputs a PWM for each pot, I haven't seem any other fuctionality, so I think it'd be interesting to replace it with a 555 based control circuit to either the original LED drivers, or just redo the drivers as well.

I'm quite tempted to go completely away from the original design and do a 555 based controller, the main operation of the micro was to take the potentiometer input and turn it in to a PWM to the LED driver side, which seems easily replaced by a 555 based circuit

Nice walk through of the debug process.

You could find a way to get the code, but what fun is that.

Clearly you have a neat project to build a new controller.

It is brave to video skills and techniques because everyone can comment on how to do it better. Don't let it stop you though. Hopefully everyone learns. One good test in a situation like this is a smell test - burn components usually smell burnt. It can narrow down the possibilities before a lot of disassembly. I doubt the fumes are healthy though.

A thing to consider for the future. Did the processor fail and short out the regulator - or did the regulator fail and kill the processor. - we can't tell.

WE don't have the full schematic but its certainly possible for regulators with small ceramic input caps to get overvolted by external supplies.

See this Linear Technolgy App Note: https://www.analog.com/media/en/technical-documentation/application-notes/an88f.pdf

While you are re-building you might like to mitigate against this effect if necessary.

You could have a lot of fun actually testing the effect on your working lamp - but perhaps not such a good idea

Should have used a 7805/LM317, I'm sure that cheap CMOS LDO got up to no good when the 15V supply is plugged in.

At first sight, the MCU appears a bit overkill for just dimming the LEDs. However perhaps they have just standardised on parts as some of the other models have to drive a small display screen.

I was wondering what killed the MCU though. Did a failure in the driver dump 12v through the GPIO perhaps, which caused a short which killed the MCU regulator ? Quite often it is the LEDs that fail first as they are often pushed hard to get maximum light output. Chain reaction.

I know posting the same idea 4 minutes later makes me look like even more of a goof than usual! 

But yes, I would be interested to  know if the MCU is bringing anything interesting to the party. Or is it just doing basic telemetry to for overtemperature and battery SOC shutdown...