Making My Weller Well...er

Discussion in 'General Electronics Chat' started by to3metalcan, Aug 15, 2014.

  1. to3metalcan

    Thread Starter Member

    Jul 20, 2014
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    So, I scooped an old Weller WCC100 solder station out of some junk that was being recycled at a previous job and then forgot about it for about a year. I finally got around to plugging it in about two weeks ago, and (naturally) it didn't work. So I disassembled it, tested some parts and found that the heating element was okay but the thermocouple was open-circuit.

    I overpaid for a replacement on eBay because it was now a Project (and I'm sentimental, I guess.) The replacement was NOS, and I installed it with high hopes, but the iron still didn't even get warm. Booooo.

    Since I'd already invested money in it, I plugged the unit into an isolating variac so I wouldn't hurt myself and started poking around. Eventually I found the problem on the control board (Item #WCC106, not that it does me any good.) The triac isn't getting switched. To test my theory, I shorted the two main terminals with a 22-ohm power resistor, and immediately the iron started getting hot, and the thermocouple started registering activity on the voltmeter.

    I can find the control board for $55.00 on eBay, but that feels like good money after bad, at this point (especially since they used to go for $5.75/ea), and only having one of them makes me leery that the iron's going to end up junk the next time something blows, anyway.

    So...there's a 16-pin IC on the board that's clearly connected to the gate of the triac, but its only identifying marks say "WELLER 185 9301." This doesn't cross-reference to anything I can find. I tried to take some pictures, but my phone just doesn't cut it for close-ups...if this thread continues for very long, I'll try to borrow a camera. In the meantime, I've cropped the stock picture from the eBay auction and attached it. The triac is an L4004F91. The other big component is a 4.7Ω power resistor that I think probably drops the line voltage. The two electrolytics are 47μF 16V (big one) and 2.2μF (small one.) There are two bigger black and white diodes that look like rectifiers, and one smaller red diode that could be a small-signal or a zener (the tests I did were inconclusive.)

    Triacs are kind of an unfamiliar component to me, but removing it from the circuit and checking it with my ohm meter, it seems to match up to what my reading on the topic says I should expect. Based on the datasheet, it seems healthily over-spec'd for the application, anyway, so tentatively I doubt it's bad. **I would welcome some info about the turn-on conditions for high-voltage, high-current triacs**

    The limited information I could dig up on the web about the inner workings of the station suggests that the controller isn't doing anything more sophisticated than comparing the amplified thermocouple voltage to the voltage from the temperature selection pot and turning the triac off when the former exceeds the latter. I'd test more to verify this, but frankly the overall circuit kind of baffles me...I don't even really know what to treat as common/ground in a circuit like this. I don't know what voltages to expect, or what to use as a reference to measure them from. There is an earth-ground connection, of course, but it only connects to the iron chassis and the heater...the board makes no reference to it. My secret hope is that one of you will look at the IC and the circuit in general and say "Aha! That's clearly a rebranded xyz!" and I can replace the control chip, but failing that, any insight at all would be a huge help!

    The third possibility I'm considering (if repair isn't a realistic option) is designing a new control circuit. This would not only make me happy, I would consider it a favor for the general public...there's lots of these stations out there, it's silly to have to throw them away because Weller stopped supporting them. If we end up going that route, I'll make sure the schematic is not only posted here, but disseminated far and wide. I have a temperature probe, a baggie of precision op amps, and general specs on Type J thermocouples...how hard could it be? :rolleyes:

    Either way, I'm now interested in such circuits, so any information, guidance, or reference materials on thermocouple-based circuitry and/or triac control circuits would be much appreciated (or, you know, if anyone just so happens to know where to find a circuit that could be adapted for this purpose!)

    Thanks!!
     
  2. shteii01

    AAC Fanatic!

    Feb 19, 2010
    3,387
    497
    Never use phone for good photographs.

    Use cheap digital camera on a cheap tripod.

    I am getting to a point where if I see a phone photo, I will simply ignore the post, no matter how interesting the topic is.
     
  3. to3metalcan

    Thread Starter Member

    Jul 20, 2014
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    Yeah, that's why I didn't bother. I looked at the pictures I had taken and thought "if I was troubleshooting this, could I tell anything from these pics?" and the answer was sadly no. The picture that is attached is from someone auctioning one of the boards. I'll post some better ones this weekend...got a friend who's going to loan me a camera.
     
  4. atferrari

    AAC Fanatic!

    Jan 6, 2004
    2,648
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    I ask for a better picture and wait. (Never close dorss unless I want to kill the guy).:)
     
  5. Lestraveled

    Well-Known Member

    May 19, 2014
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    The IC may be a TDA1023. It is a temp control IC that drives a triac directly, and it is 16 pins.
     
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  6. to3metalcan

    Thread Starter Member

    Jul 20, 2014
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    Looking up the DS now!
     
  7. to3metalcan

    Thread Starter Member

    Jul 20, 2014
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    I'll have to wait until I'm home tomorrow to know for sure, but this actually looks really likely based on my memory of the layout. Updates to follow! In the meantime, if anyone wants to weigh in on thermocouple or triac theory, I'm still interested in learning!
     
  8. Lestraveled

    Well-Known Member

    May 19, 2014
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    If it is a TDA1023 the only place I have found them so far is on Ebay, from China, for about $24 each.
     
  9. to3metalcan

    Thread Starter Member

    Jul 20, 2014
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    That's kind of a bummer (still over a 50% discount vs. the whole board!) but the chip itself may not even be bad...with some help from the datasheet, I may find another problem in the external circuitry.
     
  10. Lestraveled

    Well-Known Member

    May 19, 2014
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    Let's hope.
     
  11. MrChips

    Moderator

    Oct 2, 2009
    12,440
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    First step, replace the triac. Q4004 triac is common part.
     
  12. to3metalcan

    Thread Starter Member

    Jul 20, 2014
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    Good call. I don't have much faith that it'll make a difference, since I don't see any activity at the gate terminal, but might as well eliminate it as a possibility.
     
  13. inwo

    Well-Known Member

    Nov 7, 2013
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    100 ohms from MT2 to gate will turn on triac to test it.
     
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  14. business_kid

    New Member

    Feb 5, 2013
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    I start with the temperature sensor. Have you data on that? if not, your temperature is going to be guesswork. Don't invest in an obsolete iron, that's my advice. It's a victim of planned obsolescence, and if you fix it, the element is not far behind, and the switch. Do you need Weller anyhow?
     
  15. Lestraveled

    Well-Known Member

    May 19, 2014
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  16. KJ6EAD

    Senior Member

    Apr 30, 2011
    1,425
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    That's nice but beware the handle of the PES51 pencil that goes with it will eventually start melting and the replacement costs almost half the price of a new station.
     
  17. Lestraveled

    Well-Known Member

    May 19, 2014
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    I have owned a WES51 for about 3 years now without any issues. I bought it when I retired my 30+ year old WTCP.
     
  18. to3metalcan

    Thread Starter Member

    Jul 20, 2014
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    Business, as per in my original post, replacing the thermocouple was the first thing I did...it's a type J and they're pretty well documented. Everyone else, I *know* fixing it is not is the strictly practical choice! I hate throwing things away, and I'm also using the opportunity to educate myself on some components and processes I'm not familiar with...these days, cheap temp-controlled irons are everywhere. This one'll see relatively light duty if I get it fixed.
     
  19. to3metalcan

    Thread Starter Member

    Jul 20, 2014
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    Inwo, thanks for the tip! I'll try it tomorrow.
     
  20. MrAl

    Well-Known Member

    Jun 17, 2014
    2,433
    490

    Hi,

    Sorry to hear about your demise, i know it can be frustrating sometimes.

    To take a close up picture or several pictures, find the largest magnifying glass you can find and hold it in front of the lens. If you can see a preview on the phone you can move the phone and lens closer and farther away from the subject, and away from each other, and see what works, and watch the light angle as that can cause glare if it's not right. The light should be mostly on the subject and not too much from behind the lens.
    You can get some decent although not perfect pictures this way even though the mag glass is not corrected for color nor spherical aberration. The pic could look a little strange, but with a little experimentation you can get some pretty nice photos that are at the very least usable.

    The basic theory of the controller is it measures the voltage of the thermocouple, corrects it for room temperature, then uses that signal as feedback to a variable with pulse circuit that triggers the triac repeatedly twice every power line cycle and that varies the power to the iron and that varies the temperature, keeping it somewhat steady.
    The control circuit for something like this is quite straightforward, the main difficulty is getting a circuit to properly read the thermocouple. You have to find out what kind it is (probably K but who knows) and then look up some circuits on the web. There has been a lot of progress made in these kinds of circuits over the years and there are some special IC's made just for that. You're probably better off going with that kind of IC rather than winging it with op amps.
    The control circuit could consist mainly of one or two LM358's or one LM339 for example.

    The triac is triggered by a small gate voltage and current. The current has to be a minimum level, depending on the triac it can be as low as 1m or as high as 75ma. If you get a data sheet for the triac it will tell you more, and what is the best gate polarity to use (negative usually works best, but it depends on the triac).
     
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