Hakko 888 earth connection and extra pin

[KL27x]

I was soldering on a powered board (3V, lab supply!), and oops! My new 888D has a grounded tip. This is weird, because I had the thing open just the other day, and I swear I saw a 1Mohm resistor in there between the earth wire and the pin on the socket.

So here it is.



Turns out the earth is connected directly to the tip of the iron. And the 1Mohm resistor is connected to an unused pin on the socket. I wonder if Hakko meant to do it the other way? Or if they put that resistor there just to make it look like the 888's 6 pin DIN handpiece was more special than its predecessors which used a 5 pin DIN? Or if Hakko is so anal they think a DIN pin which is not even connected to anything needs to be grounded thru 1Mohm resistor?

 

Any rate, the existence of this unused pin and mystery resistor make it easy to change the grounding from direct to 1Mohm by snipping the earth and resoldering it on the other pin:

[KL27x]

BTW, in these pics you can see where I soldered the jumpers for the preset mod I did, catching the +5V and ground and button traces to automate preset selection with a microcontroller and button/led board attached to the front of the station. For the time being I have quasi-retired my analog station as a backup, stowed in the nice new box I got with the 888D. They don't make 'em like this, anymore, and it has earned a rest. This 888D is going to be my main station, for now, as I have gotten used to the digital station I use for travel, and my mod board has not let me down, yet.

I found I missed the power and heater LED on my analog station; due to where I put the station under my bench, I can't easily see the top half of the station to see the digital display while I'm seated. So I added 3 indicator LEDs at the bottom left of the station. That's the other mess you can see in the pics. I found out I didn't have any regular LEDs - I'm down to nearly all SMD prototyping components, ATM. So I made some bottom shining LEDs with 0603 LEDs and protoboard. And drilled 3 holes for them to shine through a glob of hotsnot. Works great. You can see where I picked up the heater signal from the dot of the 7 segment.

[tooki]

I've never heard of grounding a soldering iron tip via a resistor. My Ersa i-CON nano certainly doesn't, its tip is direct to ground.

If I had to hazard a guess, it's that on some other models of handles, there's a conductive ESD-safe part of the handle, and because it's in contact with human skin, needs the 1M protection resistor.

[KL27x]

^ I do it so I can solder on a live circuit. Low voltage stuff... USB port or lab supply. Cuz sometimes solder and a fly wire is most expedient and turning off power is maybe not necessary while debugging.

There is argument for those working on mains that making sparks, letting out the smoke, and/or popping your circuit breaker is a nice reminder that your circuit is live. This is a valid argument. (A steel or copper bench directly earthed would also be a protective feature! ) But this is personal safety issue which has nothing to do with ESD to components. ESD is when kV of surface charge zap things. A few mV of inductive AC on the tip might destroy SOMETHING out there, but it won't be via ESD.

I suppose you could add a switch to select between one or the other, if you wanted. Direct earth when you want EP (Electrocution Protection). And 1Mohm connection for the very marginal need to add ESD dissipation to the tip, in case you are able to generate a surface charge on the plastic handle. Personally, yeah, I don't see a huge reason to have 1 Mohm resistor over no connection, at all. But it's there, so why not? If I could solder a connection inside a box, close it up, and never see it again, it's not like pulling on a wrist strap and connecting it every time I sit down.

For some reason we equate ESD-safe iron with grounded tip. I didn't start that trend.

[stj]

maybe the extra pin & resistor is/was for a different iron - a so-called anti-static variant with a conductive shell.

[alm]

Tip hard connected to ground is pretty common. Does not seem optimal for ESD. Maybe it is a safety issue? Blowing a fuse / GFI would be preferable than having some high voltage on the tip (which is usually very close to the handle and finger holding the solder).