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Help: main board in reboot loop during initial assembly

Posted: Sat Apr 11, 2020 1:49 pm
by psurry
I purchased the DSO Shell kit from banggood (board p/n 109-15000-00E2) and tested that LCD powered up with some loading screen before assembly, and then disconnected power, but I didn't pay much attention to what was on the screen.

I carefully soldered the parts in step 1 and removed R30, then applied power again but now the board seems stuck in a reboot loop. I've checked all my soldering and doesn't seem anything obvious wrong or how I could have interfered with something during that process?

When I turn on the power switch the LED at D1 flashes once along with the LCD flashing white, then the screen goes dark and the cycle repeats with about one second cycle time. From what I've read that seems like the STM32 reboot cycle as if the flash was inaccessible/wiped, or JP0 boot pin was pulled high? but JP0 is open.

When I measure voltage from DGND => V+ I can see voltage fluctuate between 0 and 9V(?) in the same one second loop altho it's hard to get a clear reading with my multimeter.

Another possibility might be brownout I guess, what power should I expect the board to draw?

[Update]: with a 9V battery instead of the 9V wall-wart supply I was using, I don't get any LED or screen flash, but voltage across battery terminals is pulled down to ~3V and the STM32 chip on main board gets super hot within a second or two - short somewhere??

Any recommendations for steps I can take to debug?

Re: Help: main board in reboot loop during initial assembly

Posted: Sat Apr 11, 2020 1:53 pm
by psurry
Here's a photo of my main board

Re: Help: main board in reboot loop during initial assembly

Posted: Fri Apr 24, 2020 1:39 pm
by psurry
I did some continuity tests on the main board, without the analog board connected, and no power (after several days).

From DGND i see continuity to all of these: V+, 3.3V, VDDA, GND, *all legs* of voltage regulator U3, 1 leg of power socket J7

No continuity from DGND to either leg of diode D2, TRIG, TL PWM, RX1, TX1, D-, D+, RESET.

Can someone with a good board confirm which (if any) of these look bad? Trying to figure out where to start removing parts.

I'm suspicious of the voltage regulator but not sure how to test it.

Thanks,
Patrick