1708 MCU faulty. No power

[Andrunin]

Hi, I've got another puzzle here with a faulty MCU board that prevents the controller from turning on. Both battery and USB are not working. I checked the power board with a known good MCU and it works fine.

When I plugged it via USB, the other parallel USB devices were acting funky so I pulled out immediately. Stupid I know.

Visually the board looks good. I couldn't find any shorted caps with my DMM. Not sure what to look for here. Any advice?

[RDC]

Use a benchtop PSU and inject 3.3v into the MCU board at J5p4 and see if anything gets hot quick.

[Andrunin]

Thanks, I don't have a PSU atm but ordered a cheapo one and it's on the way. I tried the poor man's voltage injection with two AA batteries but it was only 2.8V and I didn't notice anything with the IPA evaporation. Probably not enough power.

Also I just saw the PSU I ordered can only do max 2 amps. Do you think that's enough or should I get a better one with more power? I planned to build my own from an ATX PSU but this one was dirt cheap.

[RDC]

You're not trying to weld anything with it, or nuke whatever is bad into oblivion before you get the chance to identify it. So a couple of Amps is more than enough for doing anything game controller and small project related. If it also has the ability to limit the current it outputs that's better than a homemade setup that doesn't have that feature, so you can start low and work your way up, or see that it's pulling in excess of 2A, versus just connecting it to an ATX 3.3v rail that could have 15 or more Amps on it.

[Andrunin]

True. The PSU arrived and it can limit the max current.

The board is not drawing any current, so I guess we have a break somewhere. I can poke around a bit and test traces for continuity. Do you know what chip or component is critical for powering this thing?

[Andrunin]

I tried the same thing with a good board and the PSU says it's drawing 50 mA. Is that a good reading? On the bad board it says 0


The PSU seems to work ok because it powers a good controller when I connect it to the battery terminals

[RDC]

A working board will pull around 50mA or so.

Only things I could see causing it to be that dead is a bad J5, bad solder joint at J5p4 or the trace right at J5p4 is damaged in some way.

[Andrunin]

J5 and the traces are good. I checked everything with the DMM. Nothing shorted and I checked the trace from pin 4 to each pad. Also I can measure 3.3V at C7.

I discovered also that when I slowly up the voltage from 0 to 3.3V, it does end up drawing 30mA. When I turn the PSU off and on at 3.3V it's dead. So it doesn't like the jump start at 3.3V.  Nothing is getting hot at 30mA.

Then I also joined it with the power board and put 3V at the battery terminals. When I turn the controller on, it just draws 10mA and doesn't power up.


Any idea what component could cause this symptom?

[RDC]

It's most likely the MCU, or something on that smaller MCU board, possibly water damage or corrosion under the MCU since it's a BGA chip.

[Andrunin]

That's a bummer. I took of the shield and tried to reflow the MCU but it didn't change anything. The board looks brand new and there are no signs of water damage anywhere. Welp, I don't think I'm capable of reballing it. Could also be a bricked firmware flash. The board is still good enough for spares I guess.

[RDC]

If you run across another 1708 you can swap the whole castellated board, maybe from one that had the Sticks or Triggers butchered on. That's still quite a fun swap, but easier than an MCU reball without the proper setup.

[Andrunin]

Actually I have another MCU board that is in a very bad state. I wonder if a swap is worth a try now. Apparently somebody tried to fix the controller, but two diodes on that little castellated board were ripped off and sticking on that clear orange tape lol.

I desoldered it out of curiosity and also removed the shield. There are also some bad scratches and a ripped of pad for a smaller diode:



I marked the problematic areas that I could find here. When I took that shield of from this board I moved and lost smaller components top left of the MCU, but I can replace the components here with the parts from my other board.

I don't know if this MCU works or not. The board looks pretty beat up, so idk if traces are broken and whatnot. Do you think this one is toast or is it worth the trouble to replace the components?

[RDC]

I doubt I'd mess with repopulating and going over all that on a board I wasn't sure even worked, but that's your time and effort there.

[Andrunin]

True. It seems like it has a couple internal PCB layers and I don't know if there are any broken traces. If it wasn't for that I'd give it a try, but I have a couple other things to tinker with here. Thanks anyway for all the advice.

[VaNDAL_UK]

The 1708 MCU PCB's are very low quality, pads and traces pull easily and the MCU boards crack and sever traces. I have a tub full of these boards that are cracked. Mostly from rage quit and having the controller slammed face down punching the analog modules through the board. Unless you have a microscope will be difficult to diagnose.