Rev 3: Hot MOSFET & low Voltage

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11 months 4 days ago #10402 by rmcrae
Honestly? Essentially, none--newer hobbyist, sorry.

In the future what do you recommend? I already own a grounding strap, but I couldn't tell you that I honestly know how to use it efficiently.

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11 months 3 days ago #10403 by Ty_Eeberfest
I agree - bad MOSFET. Those voltages are as expected. The external power supply and low voltage section of the clock now working as they should now that the always-on MOSFET isn't creating what was essentially a dead short. I believe the Modular kit uses an IRF-840 so yes, there is a risk of damage by ESD (static).

At this point you could either buy an IRF-840 (not IRF-840A) or get in contact with Ian using the contact info on his store site. He's pretty generous with replacement parts, especially in a case like this where the part could have gotten zapped anywhere: storage, packing, shipment or assembly. He's in Switzerland so depending on where you are it could take a while to get a replacement from him.

As a hobbyist I an shamefully careless about ESD protection. As an EE I should know better. :S My excuse is that my branch of engineering doesn't involve working with PCBs and individual components very often. Anyway, when I'm putting together a board I work barefoot, which does a fairly good job of bleeding off charge to the floor (as long as feet are on the floor!). I use a soldering station made by a reputable company and marked "ESD Safe", which basically means the tip is grounded / earthed. I use a wrist strap occasionally but not consistently.

The idea of the wrist strap is to connect your body to earth ground through a substantial resistance. This bleeds off charge but limits the current that could flow if you accidentally grabbed onto something that was live and earth referenced. The end of the wire should be tied to ground. In a North American outlet the center screw that holds the cover plate on is usually a good source of grounding. Other places I'm not sure. You just ground the wire and wear the strap while working.

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

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11 months 3 days ago - 11 months 3 days ago #10404 by Torsten Lang

rmcrae wrote: Honestly?

Yes, honestly. You're working with ESD sensitive devices and should take care about. As an EE myself I honestly have to tell you that at my private workspace I also haven't installed all of these countermeasures, but if you know how to prevent electrostatic charge...

As Ty already mentioned it helps working barefoot (or as I do having ESD shoes which are not even expensive) - I use both options one or the other time. It also helps a lot to wear 100% cotton clothing.

Furthermore, it's best to complete the surroundings of the sensitive part first (any capacitors, resistors etc.) so that at the time you solder the sensitive part its pins are not open (that also requires that no connection ends e. g. at an empty socket ;-) ). You can also short the pins with a wire near the case until you've done the soldering.

Most digital integrated circuits today are protected very well against ESD. But not discrete parts. And certain parts like MOSFETs don't forgive wrong handling...

Regards,
Torsten
Last edit: 11 months 3 days ago by Torsten Lang.

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10 months 3 weeks ago #10406 by Ty_Eeberfest
Has this been resolved?

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

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10 months 3 weeks ago #10407 by rmcrae
Theoretically yes. Still waiting on the new MOSFET to come in. Will update once it is installed.
The following user(s) said Thank You: Ty_Eeberfest

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10 months 1 week ago #10437 by w8an
If you do much of any component work, I would highly recommend that you get an anti-static bench mat to build and repair upon. This is all I use, but it does require a bit of discipline. If you move about the room or do anything that could apply a charge to you, just lay your hand on the mat for a second or two before touching your work. After a while the action just becomes automatic.

Desktop antistatic mat
Another one

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