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?
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!!
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?
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!!
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