Itsy Bitsy M4 Express - Forensics?

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xanatos
 
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Joined: Thu Jun 18, 2009 3:09 pm

Itsy Bitsy M4 Express - Forensics?

Post by xanatos »

Curious if you folks have any cause-of-death forensic capabilities for these modules. Had one in a project that was working well for a couple of months. Then I went & got covid, so the project sat in my office for a week or so, then sat a few more weeks while I got caught up on everything. When I finally picked the unit up & switched the power on, nothing happened. Not even the flashing light on the module. I checked battery power, all good. I suspected my 5v Buck regulator supply (CKCS CK1408 - nice units) first, and saw 0V coming off of it. I started disconnecting things and when the power to the IB M4E was disconnected, the buck regulator immediately returned to outputting 5.02Vdc. I put power to the IB M4E separately and found it was pulling a lot of current, and on touching it it felt warm to the touch. I tested all other attached components & modules with a new IB M4E and they all tested fine and everything is back to working now, on the new module.

Apparently the IB M4E failed due to lack of use :) I'm truly curious as to what actually failed on the module. It was enclosed, stored in a nice safe, dry location, worked when I powered it off last, didn't work when I powered it up after that. If I'm doing something here I'm not aware of, or if my system is somehow throwing a power spike on shutdown or power up, I'm not seeing it on my scope... I'd like to have some certainty of how the failure occurred before I start building more of these using the same components.

Not sure if it's possible or something you have the capabilities of doing - so I figured I'd ask just in case you have forensic failure capabilities available :)

Thanks,

Dave

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mikeysklar
 
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Re: Itsy Bitsy M4 Express - Forensics?

Post by mikeysklar »

Dave,

Good question about root causing a dead board. Not an easy task.

Are you able to see any sign of life when powering off the BAT pin (3.5v - 3.6v)? I would assume not, but was curious if connecting another way would help.

Was there anything else connected besides the power supply?

How did you have the buck connected?

Can you take a high res image side by side a working and non-working IB M4E to see if there is any noticeable component damage?

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xanatos
 
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Re: Itsy Bitsy M4 Express - Forensics?

Post by xanatos »

Hi Mike,

Power was supplied from the output of the buck regulator to the BAT connection on the M4. An attempt was also made to power up via USB port with no luck either.

The M4 was hooked up to an Adafruit 1.14" 240 x 135 Color TFT Display (ST7789), a voltage-divider style light sensor (CDS cell) used to control PWM to adjust the brightness of the display for ambient conditions, two buttons for up/down control of the output signal on A0, which fed a laser diode driver module with a modulation input.

I did a visual inspection of the unit with a 10x optical loupe but revealed nothing immediately suspect. Below is a photo of the failed unit and another of my spares for comparison.
M4 Forensics.jpg
M4 Forensics.jpg (290.5 KiB) Viewed 173 times
Thanks,

Dave

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alpierce
 
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Re: Itsy Bitsy M4 Express - Forensics?

Post by alpierce »

What was the VHI pin driving?

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xanatos
 
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Re: Itsy Bitsy M4 Express - Forensics?

Post by xanatos »

The VHi pin was driving the ST7789 display only.

Dave

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