Glitching out and mosfet overheating.

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7 months 3 weeks ago - 7 months 3 weeks ago #10085 by Phil_Mod3
AFAIK, you can't directly check the oscillator with a multi-meter since a) the signal is fast and small and b) the added capacitance by probing the circuit could stop the oscillation. First, you could check it visually, also try to clean the PCB from remainders of flux.

Ty has a good point, R7 should pull down the gate voltage. Maybe check that part of the circuit as well.

If your multi-meter is able to measure frequency, you could connect it to the HVD test point and see what happens when you touch the tab. Since the MOSFET gets hot, it is stuck in on state or remains in on state for too long time (switching frequency too low). If the controller stops working completely, the frequency signal will disappear (frequency = 0). I am not sure if a slowed down oscillator is possible, but in theory, the HVD frequency would also reduce then.

Is the probability of the mosfet becoming warm/hot when glitch appears 100%?
Does the glitch happen regardless of how long you touch the tab?
Last edit: 7 months 3 weeks ago by Phil_Mod3.

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7 months 3 weeks ago #10086 by daddyfredregill
When it was glitching out it would only get really hot if all the digits were blank. Sometimes it would just reset the clock, like when you turn it on and off. It shoes the version number then just resumes.

Could flux residue be the culprit? I did not know it could cause issues.

I am at a loss right now. I have been running the clock for almost 2 hours without handling it and it has worked fine. I can just hear a slight crackling noise.

I just tested it by picking it up and tried to make it glitch out but it is stable.

I do remember last night before I quit working on it i took a small pick and scraped off some fkux residue.

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7 months 3 weeks ago #10089 by Ty_Eeberfest
Flux around the crystal's pins might have some effect on the stability of the oscillator although it's a bit of a long shot. Regardless, there should be NO flux residue anywhere on the board even if the flux is so-called "no clean" flux. Mechanical removal (scraping) is not sufficient - chemical removal is the only sure method. Commercially available flux remover spray or straight Trichloroethylene are ideal. Isopropyl alcohol will do if that's all that's available. So-called "methylated spirits" (not "mineral spirits"!!) would probably work too.

Leaving flux residue on boards is bad for many reasons.....

Look into it later when the dust is clearing off the crater.

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7 months 3 weeks ago #10090 by Ty_Eeberfest
Also... I did not realize "glitching out" included spontaneous controller resets until I read your latest post. Interesting but unfortunately this is a chicken / egg problem: is the MOSFET getting "stuck on" and causing the reset (because it's effectively shorting VIN to GND when on) or is the controller flipping out / crashing, leaving the MOSFET on, and eventually resetting on a watchdog time-out (or something)? Let's discuss...

Look into it later when the dust is clearing off the crater.

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7 months 3 weeks ago #10091 by daddyfredregill
Give me a few minuites. I am uploading a video to youtube so you can see.

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7 months 3 weeks ago - 7 months 3 weeks ago #10092 by daddyfredregill
Here is the clip. In the video everytime i had to put my hands down is when I killed power. Near the end I only used one hand and could not get it to act up. Then the last time before the end of the video the mofset started to heat up and smoke.

It is very speratic and seems to be only affected with two hands. This is so wierd and honostly beyond my scope of knowledge. I am fairly good at soldering. I figured it would be a simple build.

Sorry for the bad video

Last edit: 7 months 3 weeks ago by daddyfredregill.

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