I went to the only local electronic part store eons ago to buy replacement part for my older soldering iron. It was a decent iron that lasted such a long time that the store no longer carry the replacement parts. I bought the WESD51 as it was on a back to school sale and Wellers parts and accessories was easier to find. It was a lemon. Ironically the serial number happens to be 0404 (Quality not found!?)
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| 4 hidden screws under the rubber feet |
Right from the start I had a lot of issues with the iron not reading its temperatures correctly. I thought it was a connector issue, but later I found that it was a manufacturing quality problem. They change a PTC fuse into a larger package (green 2X2 at top of PCB) but didn't do a good job of touching up the soldering on the mismatched footprint. So I had to fix it up in the first few months.
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| Control PCB |
A trimpot has limited cycles, so personally I wouldn't use it for a temperature control knob. It did last a very long time, but obviously not long enough vs the rest of the iron. A few months ago, the temperature setting started jumping beyond my set point due to wiper contact issues. I knew I had to repair it.
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| PCB back side |
As I was opening it up, I found out that they didn't do a proper crimping job on the AC leads of the power transformer as they tried to crimp a tinned wire instead of bare wires!? Solder is soft, so eventually the wire came loose.
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| Poor crimp job |
Here is the cheese knob for the trimpot. It was held together with a self tapping screw. I had to put in some hot glue to hold the screw.
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| Cheap plastic knob for the temperature control |
I ordered the smallest
10K linear potentiometer I can find and they arrived today. I couldn't find any 2K pots. Since it is to provide a 0V to Vcc to the ADC. The increase in source impedance could affect the ADC result. One way to fix it it to wire a 0.1uF cap from wiper to Gnd, but that is not needed here.
They are not the greatest quality, but I got a bag of 5 for cheap. They came with washer and a nut. I use a pencil to trace the outline of the washer on the PCB and milled out a notch for the locating pin.
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| Modification to the PCB |
I mounted the pot onto the PCB and soldered the pins to the existing pads with wires.
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| Pot connections |
I had to remove a bit of the material in front case to clear the mounting hardware for the pot.
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| Making room for the mounting hardware |
I use a reamer to enlarge the hole, so that the PCB can be mounted flush.
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| Old Radio Shack reamer |
It ain't pretty as it is soft plastic. The hole is hidden away by the knob. The shaft is barely long enough.
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| The big hole I made |
I broke off the cheesy plastic off the knob. I got some cheap
plastic knob from China that is small enough to fit inside the cavity.
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| Temperature control knob |
It wasn't tall enough nor wide enough, so I had to improvise. I melted about 1/2" of hot glue stick with my hot air tool set at 120C in the cavity.
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| Hot glue to the rescue |
I pushed the plastic knob into the molten hot glue and wait for it to set. I filed down the knob so that it is flush. I added some extra hot glue for support on the sides as well.
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| Improvised knob |
One of the things I did to prevent the plastic mounting post from splitting was to use a piece of cable around it. I wish they would use threaded inserts.
