Problems with Arduino UNO Nixie kit - high voltage

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5 months 3 weeks ago #11305 by albert
Ok! I just tried something..I bent the legs of the MOSFET and it started working! So it looks like this component is not great. I will order a new one from a local webshop and try if that works. Thanks for your help :)

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5 months 3 weeks ago #11306 by judge

albert wrote: Ok! I just tried something..I bent the legs of the MOSFET and it started working! So it looks like this component is not great. I will order a new one from a local webshop and try if that works. Thanks for your help :)


That could mean it is not well soldered in, so you should try touching up the solder for the MOSFET. If you still want to replace it, you would need to replace it with the exact same model - each model is very different.

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5 months 3 weeks ago #11307 by Ty_Eeberfest
Albert, is there any possibility that the metal tab of the MOSFET was touching something metal (conductive)? The metal tab is not isolated - it is internally connected to one of the pins - so if the tab touches something conductive it can cause trouble. In your pix it looks like it's probably okay but you should check it anyway.

If you do end up replacing it use great care when removing the old one! It's very easy to damage the board when de-soldering. I suggest cutting off the leads and then you can de-solder and remove the stubs one at a time. Much easier that way than trying to do all 3 in one go.

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

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5 months 3 weeks ago #11309 by albert

judge wrote: That could mean it is not well soldered in, so you should try touching up the solder for the MOSFET. If you still want to replace it, you would need to replace it with the exact same model - each model is very different.


Maybe I was a bit too quick with my conclusion indeed. I did what you said, but to no avail. Still the same..weird.

Ty_Eeberfest wrote: Albert, is there any possibility that the metal tab of the MOSFET was touching something metal (conductive)? The metal tab is not isolated - it is internally connected to one of the pins - so if the tab touches something conductive it can cause trouble. In your pix it looks like it's probably okay but you should check it anyway.


I have checked it and it doesn't look like it's touching something on the board.

Ty_Eeberfest wrote: If you do end up replacing it use great care when removing the old one! It's very easy to damage the board when de-soldering. I suggest cutting off the leads and then you can de-solder and remove the stubs one at a time. Much easier that way than trying to do all 3 in one go.


That's exactly what I was thinking last night :) Thanks, that confirms it is the right approach.

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5 months 3 weeks ago - 5 months 3 weeks ago #11322 by albert
Hi, I haven't received a new MOSFET yet. But, because the clock did run for a few hours I thought maybe I didn't require a new one. After a while I noticed a burning smell, so I checked the MOSFET. It was burning hot. What can cause this? Is it likely that this component is bad? Or can this be caused by bad soldering / other broken components? What can I do to test this? Thanks

Edit: I forgot to mention: the clock stopped working after a few minutes after I noticed it was hot. Powering it off and on again fixed it, but I'm afraid that there's something wrong anyway.
Last edit: 5 months 3 weeks ago by albert.

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5 months 3 weeks ago #11324 by Ty_Eeberfest
The MOSFET is pulsed rapidly to "charge" and "discharge" the inductor. If the pulse-on time is too long the inductor saturates and the MOSFET heats up. The duty cycle of the pulses is initially set by the HV calibration routine that runs the first time you power up the clock. Once initially set it is adjusted, based on feedback, in real time as the clock runs.

Since you were running with MOSFET problems for a while you should try re-calibrating the HV parameters. Do a factory reset (hold the button down while turning on power), The display should start counting 0 -9 repeatedly. Press the button while the display is showing all 8s to start the HV calibration routine. There is a good chance this will solve the overheating problem.

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

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