How to convert the Hakko FR301-82 for North America

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Motivation
First of all, WHY would anyone want to do this? The answer is that right now, you can import this tool from Japan to America for only $160 (just check eBay). By contrast, the American variant sells from Home Depot currently for $278.48, and direct from Hakko USA for $340.67. If you buy from Amazon, the reviews there say you will most likely get the Japanese variant anyway, but at a more premium price of $204.

Most likely, the cause for the majority of this price difference is the "Weak Yen". Lately, you get a lot more Yen than you used to when you convert $1 USD to the currency used Japan, which means that $1 USD in Japan has more buying power than is normal, and this is a situation that has been ongoing for at least a year now.

There are very few differences between the Japanese FR301-82 and the North American FR301, which makes the conversion viable & desirable.

Background information
The Hakko FR301-82 is a variant of the well-known Hakko FR-301 desoldering iron produced for the Japanese market. Two variants are sold in Japan. The FR301-82 is a 3-prong grounded variant, and the FR301-81 is a 2-prong ungrounded variant, compatible with the more common 2-prong outlets in Japan. Needless to say, the grounded FR301-82 is preferable, since the ground wire is connected to the tip of the iron, which might otherwise transmit rogue voltages to the component you are desoldering & damage it.

It is possible to use the FR301-82 outside of Japan, and some people do in fact just plug it directly into 120VAC and are happy (for a while), but it is relatively trivial to make the conversion proper. The easiest thing to do is to just use a step-down converter to 100VAC, and since the tool doesn't use that many watts (around 100w), most any step-down converter can do it. But that's not what this thread is about. I'd like to document the differences between the Japanese Hakko FR301-82 and the North American Hakko FR301 to help those who want to run the FR301-82 safely & without failure, as designed, on 120VAC.

Foreground information
Nearly all components of the FR301 and FR301-82 are the same. The chassis is the same, the suction motor is the same, the circuit board is the same (only one circuit board used world-wide, see attached pictures). The heating element is technically a different part number, (replacement part# A5047 for North America & A5046 for Japan), but it has the same ohms resistance across the two red heating element wires (per Hakko documentation), and from what I can find online, no one has had any issue using the heating element part of the FR301-82 circuit on 120VAC without modification. The North American version is said to use 140watts to heat, and the Japanese version is said to use 98 watts to heat. The math says that this difference in peak wattage is due to the increased voltage available in North America, and not due to a difference in components used. Nevertheless, if you are nervous, just don't do this modification and use a step-down converter instead; you'll still save money over buying the North American FR301.

I bought the FR301-82 from Japan and a B5189 replacement PCB from Hakko USA to inspect every single component on the circuit board and confirm: There is only one difference between the FR301 and the FR301-82 apparent to me. Resistors in position R21 and R20 have values of 300 ohms in the North American controller PCB, and only 10 ohms resistance in R21 in the Japanese controller PCB (R20 is empty). There is also a black sharpie mark in the "120 vac" silk screened checkbox instead of the "100 vac" box. There are no other changes on the board.

Tips

• Hypothetically, you should be able to use eight "normal" 1/4th watt 1.2kohm resistors in parallel instead, if you are more likely to have those smaller resistors laying around in your workshop.
• Be careful not to lose the small spring which goes on the yellow button piece near the collection tube, or the small plastic washer that goes on the screw of the yellow back-piece, or the small captive nut that that screw screws into. Take pictures as you disassemble for easy reference.
• You may need to calibrate the temperature control, which can be done by tweaking the phillips-head variable-resistor directly above the part of the tool which lists the temperature settings. I did this by comparing my trusted Weller WES51 temperature controlled soldering iron with the un-calibrated FR-301 under a thermal imaging camera. The value that was correct for me and my specific FR301 heating element was 4.94kohms across the legs of that variable resistor, but your value may vary. By the way, I believe this calibration step is why Hakko put the "Element is heating" LED indicator on the "wrong side" of the tool; it does make calibration easier to be able to see the tip & the LED at the same time.
• If you're not sure about any part of this, just use a cheap low-wattage step-down converter & you'll still save money.

Too Long; Didn't Read
Replace resistor R20 (which is a 1 watt 10 ohm resistor in the Japanese Variant) with two 1 watt 300 ohm resistors in positions R20 and R21 (as done on the North American version). These resistors limit current to the suction motor. Congratulations! You just saved over $100 by replacing a resistor.  The heater section of the tool seems to have been designed by Hakko to use either 100VAC or 120VAC without modification.

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excellent, well written post. thanks