Weller WSM 1 teardown finds DC driven iron

Weller WSM 1 is a 40w soldering station that drives WRMP soldering pencils with RT type tipsInside you’ll find an LCD, a few ICs, and a few discrete components.

It’s powered by a laptop power supply, and that the heater is driven by a DC/DC block. That sets it apart from the cheap AC driven soldering stations we’ve seen (and built).

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  1. These things sell for around $380 USD each! Amazing… There must be more to the power supply “brick” than we think. How else could you justify the margin?

  2. Is the Soldering Iron Driver compatible with Weller pencils?

    These pencils are great (if not the best I’ve tried), but as the station itself is that pricy, it would be amazing to have an open alternative..

      1. btw note that only irons with SEPARATE SENSOR AND HEATER are supported by SID. The irons where you need to check the resistance of the heater to get the temperature readings are not supported by SID.

  3. From the looks of it the heater is driven with PWM. I don’t quite get why they included a Schottky diode, though (marked SK54C). The large D2-Pak part in the middle seems to be a power FET. Is there a version with a higher power rating? There are pads for a second FET, diode and gate driver circuit.
    I think it’s interesting that they didn’t care to smooth the signal going to the heater, although they included a shunt resistor and (I guess) high side current sense amp. Maybe the signal is averaged in software.

    1. Why would you smooth signal going into heater?! The only reason the smooth it is if you read the heater temperature by the resistance of the heater, then you need to be able to push “smooth” signal in.

      The schottky is there because they need to get the input voltage up from 12-19V to 24V in order to push enough current into heater

  4. Driving any heater with a DC current leads to destruction of the element faster than driving with AC,
    mainly because of migration of ions, it also causes destruction of the tips faster.

    1. I’ve had the small tips die frequently, but several medium-sized tips seem to be lasting. I have the WD 2M, not the WSM 1, but I wonder if they are similar. The 2M can drive two irons, and can even drive soldering tweezers and an iron. I’m not sure whether the two heated tips on the tweezers work like two irons or one, but there are about twice as many pins populated on the connector for the tweezers.

  5. this station, uses s heater/sensor and tip integrated all together, so I guess the expected life of the tip is lower then the expected life of the heater and that’s why they use DC/DC with it…

  6. The power supply is nothing special at all. 12V 5A laptop brick.

    There’s also a battery-powered unit available, which costs even more. Hence the unpopulated areas and the free space in the case.

    The only negative thing I have come across so far is that all of the available tips are somewhat small. Great for small stuff, but drag-soldering doesn’t really work.

  7. I’m trying to build my own controller for these tips, anyone know the pinout? Am i right in thinking that inside the tip is just a heating element and a k-type thermocouple? I’ve been trying to figure this out for ages, I can get the tip hot but I only seem to read junk out the thermocouple (assuming I’ve got the pins the right way round…

    My guess so far is:

    Tip: Heater +
    middle: Thermocouple +
    sleeve: GND for both

    1. Hi RAJ these types of tips use the resistance of the heater to measure the temperature..
      so you just need to read the current and voltage to get the temperature. I would advise a simple test,. connect the heater to a 12V source and use an amp-meter to read the current.. If it changes then the above assumption is correct… If not….well…..
      As arhi saint they are ESD safe so the two heater leads have to contain the information. but as to the function by witch the temperature changed, now that’s tricky…And I dont see any way to get that information other then drilling the tip and inserting a TC into it….(but could prove expensive, considering that aoyue soldering stations cost around 60-70USD….

      I’ll soon (in about a month) get one of those aoyue handles(20USD) and experiment with them…If that succeeds, that would make it a very chep very precise instrument.

  8. I see, it’s strange though that I read:

    1.9ohms from TIP to SLEEVE
    1.1ohms from MIDDLE to SLEEVE
    3.1ohms from TIP to MIDDLE

    surely the ground sleeve should not be connected to the other pins?

  9. That is verry odd…there should be no resistance (or very small from middle to tip, and high resistance between the other pins and the tip)

  10. I know that the sleeve is the ground because it’s physically part of the metal barrel all the way down the body of the tip. Weird thing is, I do read something out of (what I thought was) the thermocouple but it was out of scale. Started out at a decent temp (around room temp) then shot up to 700degC as the tip warmed up to a level where it would melt solder.

    1. “I know that the sleeve is the ground because it’s physically part of the metal barrel all the way down the body of the tip.”

      How did you them measure 1R9 from tip to sleeve if they are directly connected ?!

      I don’t have weller station here but I do have Pace with similar tip and 3 wires coming from the tip and tip to wire1 is 0R01 and tip to wire2 and wire3 is “open” (none of my dmm’s can measure it so it’s in gigaohms or more). I don’t believe Weller is doing it any different for their own cartridges then PACE is.

      Looking at the picture of the Weller driver insides I assume blue and brown wires are the heater, and you can notice a shunt resistor on the trace to brown wire and a shunt voltage amplifier right from the shunt (the 5pin smd device). It’s obvious that this driver is capable of measuring tip temperature by testing the resistance of the heater (by measuring current going trough heater), but it is also clear that it uses all 5 wires coming from the connector so it can probably drive a handle that uses PTC20 (the common weller sensor) or some other sensor type. The three wire handle – I’m 99.9% sure it’s workin as I explained.

      To check, remove your tip cartridge and them measure wires on the handle. You should measure open circuit between all three wires. Then measure your tip, you have 2 tabs on a tip cartridge and a tip itself. Test the resistances on the cartridge youself – it is possible that your cartridge is actually “dead” (that your heater is burned and that it broke insulation hence made contact with the body of the tip), that would explain why you measure 1-2R between the wires, as pushing 24V into 2R would be bit more then 50W :D

  11. Slight confusion of “tips” here. 1) physical tip of the iron, 2) tip of the headphone style connector. Sorry threw both of those in the last post without thinking.

    I don’t actually have the rest of the system, I only bought the RT8 tip for £30 to make my own controller for.

  12. thanks, Raj, could you check the resistance to the actual TIP(soldering thing).. so we could figure out whitch one of them is ESD…

    But I can tell you right now that none of this makes any sense to me…first If we assume that perhaps there is a forth wire on the handle that is connected to the tIp for ESD…these 3 wires stero phone jack things make no sense in any configuration….if there are separate PTC or K TC sensor with the mutual ground there should be absolutely no contact between them. and even the highest resistance is still way off at 3.1ohms that would take 8Amos of current or 200+W of power whitch is way too much.

    I;ll search around for some manuals…for the wdm they could have some answers..

  13. I thought it was a 12V tip. I’ve been running it on 12V and limiting the current to stay around 10-20W. I think the idea is that the PWM control is intended to keep the average voltage something less than the 40W limit. Theoretically, if the control loop is working fine then the input voltage isn’t much of a problem because the tip will be controlled accordingly.

  14. Why does that datasheet say this for the WSM1?

    ESD Safe?

    No. Optional
    grounding kit
    available soon.

    Surely it’s meant to be already ESD safe?

    If it’s true that the iron can run on 12V while reading the input current to measure the temperature, then I can try hook up the tip to a thermocouple and plot the temp against input power. This should give us the characteristic of the tip to make a simple controller.

  15. Ok I am at a loss.. there seem to be 5 wires coming from the similar RT type handle.
    I was able to dig up this data sheet..

    one advice, try to contact the guy in the top article and ask him which of the wires are connected to which pins of the jack..

    One thing that is possible is that there are 5 connections on the tip, 3 on the jack, one on the small protrusion that goes into the handle with the jack, and the last one on the fattest handle contact with the tip

  16. I think the tip has ESD capabiliti, but the WSM1 station does not plug into a earthed mains cable..so you have to bring earth wire separately to it..

  17. Oh I see. I guess it seems the 12V heater is referenced to the soldering tip for it’s ground then.

    Why are other 3 pin irons grounded separately as a third pin? Surely this is because they are AC irons, where as this one is DC so the ground can be common.

    I was also thinking… Each tip has to have a different characteristic in how they heat up because their varying shape and size. Could one of the third pins on the jack be some kind of serial interface that sends a ID to the controller, indicating what tip is used?

  18. If it has some sort of a serial interface, it will probably have a temperature readout in serial as well, I find this hard to believe
    one thing tha is for sure is that the ~3ohm resistance is the heater. at 12V that would make 4Amps or 48Wats…the resistance probably increases to level off at 40W. Can you attach a currnet mesurment tool, and measure the current change as the thing heats up? thy it with 6V or below..

  19. Adjustable bench supply powering the iron. Incrementing the voltage and logging the current to build the graph. I have a probe on the tip to log temperature. It’s all held together by some pcb helping hand crocodile clamp things.

    So I got sick of wondering, and seeing as I’ve prob blown something inside anyway, I’ve gone and opened it up.

    This is what I’ve found:


    Seems there are just two wires inside. I’ve pulled them both out now and bost seem to be different kind of conductors. They are both insulated right the way down the thin tube, and the brown wire seems to be glued to another kind of conductor as it nears the bottom.

    1. Nice, could you make a whole post on the forum about all this. How the iron looks like, how it works, what’s inside, pictures, measurements etc etc … it is very hard to follow it from the blog comments

  20. What I meant was, the circuit :) you mentioned earlier that you were controlling the current. if so are you monitoring the voltage.
    could you explain the circuitry you are using to power and monitor the heater..thanks, If’d like to you can contact me on the forum, arakis via a PM with your email, or skype so we could discuss this quicker.

  21. I’d be happy to post the entire thing when I’ve gotten into the circuit design of this thing.

    The rig I was using just now is just a direct DC connection to see what power it gobbled at different temperatures. I plan to make a small microcontroller circuit that can fit into the barrel of the pen with some buttons and leds. ie, this entire station in a pen.

    Now I need a new iron tip so will order one soon, I still have no idea what this third conductor is for. I tried putting some power down it but the iron didn’t heat up and it ate about 2A at 2V. Whatever it was, I’m sure it’s now toast!

    I’ll document what I’ve figured out so far and post it on the forum and Filip, I’ll pm you in a while. Unfortunately I don’t have skype.

  22. A while ago I did some basic measurements on this system as the bits/elements were a reasonable price but the controller was too expensive. I used this system for many jobs and it was excellent, so I did a bit of investigation but unfortunately never completed it.

    As Raj said:
    1.9ohms from TIP to SLEEVE
    1.1ohms from MIDDLE to SLEEVE
    3.1ohms from TIP to MIDDLE

    The bit is supplied via tip and sleeve from a single SCR on 24v ac and the phase never advances beyond producing an equivalent to 9v dc. The second SCR goes to another output pin which is not used by these bits.

    The ring is connected back to the microprocessor which also controls the phase angle of the SCR.

    The extra two wires from the handle are from the reed switch in the handle which operates when the iron is parked in the holder (there is a magnet in the holder).

    The ring connection is to some sort of temperature sensor but it appears to be referenced to the tip connection as when the SCR fires, the voltage seen on the ring mimics the drive voltage on the tip. This is the very confusing point.

    Please note – tip, ring and sleeve refer to the connections of the 3.5mm 3 pole jack plug and not to the bit of the iron.

  23. I noticed that about the temperature readout. Using a k-type thermocouple amplifier I got good readings but found that it hits the top rail every time the power is applied to the element. So my idea was to only read the temperature between pwm bursts to the heating element. I’ve designed a board for it, it’s small enough to fit in the barrel of the pen itself, I planned to use any old aluminium tube and turn it to size. There are two buttons and a few blue LEDs to give a bar graph kind of readout. There is also an accelerometer on the device to detect when it’s in use, the micro is a ATMEGA168. If you take a look on the forums, I’ll post the eagle files. I’ve run two boards now, the accelerometer and thermocouple amp all work, need to get a program going now. Recently I haven’t bothered working on it, might get back to it after exams and such but if anyone wants to give it a shot, feel free.

  24. I was having problems with my WSM1 – it would come up to temperature, and then randomly and inexplicably lose temperature, then overshoot to 400+, then switch off. I took it apart and found the lousiest solder joints on the pencil cable to the PCB. Looked as if it had been soldered by an amateur using lead-free solder and a soldering iron that was set 30C too cold. I cut the cable, re-tinned all the wires, cleaned up all the lead-free solder and flux that had been left on the PCB and re-soldered everything using (gasp!) leaded solder. It works fine now.

    1. I read that lead-free solder works just fine if you buy the quality stuff. Nothing wrong with using leaded solder if that what you have and it works – I just wanted to point out that it was probably the bad solder joints and not necessarily the no-lead solder itself (although the two can be related).

      1. Hah!

        I payed over 20€ for a 250g spool of the lead-free stuff – tried it once. Now I have a nice paper-weight. Set the temperature a tiny bit too low and it doesn’t melt properly (not really eutectic it seems), it doesn’t wet properly either. Increase the temperature a bit and you get instant oxidization. What a POS! I don’t know what kind of flux they used for this one, but it is USELESS.

      2. I’ve never had any problems with lead-free or silver lead-free solders. Now I tend to get them for cheap in 1mm or 0.5mm off ebay and it’s works a treat. I personally have had more trouble with leaded but that’s because it was really cheap and the flux was crap. I know it flows better, I tend to only use leaded if I run out of lead-free or I’m doing a really heavy joint like a big connector or something. Even the solder paste I use is lead-free. No issues what so ever, who cares if your iron has to be 15degC hotter. Having soldered from a very young age and very often, the thought of handling lead and being exposed to the flux fumes always pushed me to buy lead-free. I know it’s perfectly safe as long as you don’t sit there chewing the stuff but hey :P

  25. Thanks Raj. Is it true that there are problems mixing leaded and lead-free solder? PCBs are finished with leaded solder, typically, unless they’re gold plated. I was told not to use lead-free solder on a PCB finished with leaded solder, nor the reverse. Now that we’re basically off-topic, is there an appropriate thread in the forum for solder composition issues?

    1. No idea if there is a forum topic on the subject. As far as mixing goes, personally I’ve never had a problem. This assumes that you sufficiently clean the joint of old solder before applying new solder. If it’s a new board, here in the UK, most board houses only do lead free tinning. There are worse things that contaminate the purity of solder. All kinds of metals from joints, flux, plastic from wires, even crap off your soldering iron. Mixing solder isn’t too bad as long as you clean off the old stuff and use plenty of good flux to make up for it. This will mean there is very little lead solder in the mix with your unleaded solder.

  26. The jury is still out on the long tern quality and reliability of lead free solder. We began using it in our manufacturing because products exported to Europe had to conform with RoHS standards. Interestingly, the EU does not require lead free solder in automotive, aerospace, and medical industries (this ought to tell you something). The problem with lead free solder is that its melting point is about 40C higher than tin/lead, and the alloy mix has a paste phase between liquid and solid phases (unlike the 37/63 lead/tine alloy). It takes practice and attention using lead free solder as the hotter temperature required to melt it can easily lift the copper off the PCB. I’ve never had any luck wicking the lead free stuff, even with solder wick impregnated with flux that’s supposed to make it flow. I usually just add some tin/lead solder to the joint and let it blend, and then wick it up. Nonetheless, I found it interesting that a manufacturer of soldering instruments has defective lead free solder joints in its product. The PCB machine soldered joints were all OK. Only the hand soldered joints were defective.

    1. Very ironic indeed :P. I guess the whole point of RoHS was to eliminate the amount of lead waste generated from all the consumer electronics people use for a couple years before throwing in the bin. I understand lead-free solder is more brittle so likely to crack under vibration and stress. I understand the use of lead free is actually becoming more pressurised in the military and aerospace sector, but there are more worries about the formation of tin whiskers on lead-free solder rather than joint reliability.

  27. A bit off-topic, but still related to my WSM-1. Today I’ve had to retire the RT3 tip. After about 3 years of moderate usage, tip-erosion has made it almost unusable. The heater / temp-sensor are still perfectly fine, but the tip itself is EOL. It’s a bit disturbing that I have to throw all of that away, just because that tiny tip has lost its plating – and is inseparably fused with the heater. Quite a waste of material compared to bigger irons with separate tips.

    1. No. And from what I hear that will never happen – at least not when I’m the one paying for it.

  28. Can you please help me out. I have this Weller MLR21 with 24v 25w. I don’t have the station for it but still I need to fire it up and use it. It has 5 wires namely red, black, blue, white and brown. I used it once but forgotten whic wires connected to the element,. I remember I had to short 2 of the remaining wires but can’t remember . Any help will be appreciated , feeling frustrated, I use magnum as a main soldering iron. Weller is a joke compare to these southAfrican products.

    The other question dose these irons using AC or DC ?
    Thank you

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