Weller WES51 Service Manual

Thread Starter

DougPenhall

Joined Feb 22, 2019
4
I will look at it and report back later.
Wow! 6 years and you still haven't reported back. Would be nice if you did. I'd love to see the schematic because my WES51 is currently doing the exact same thing. From your description, it appears that the WES51 works just like the WD1.

Here's a list of the chips that are on my circuit board.

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PRECISION CMOS SINGLE MICROPOWER OPERATIONAL AMPLIFIER
http://www.ti.com/lit/ds/symlink/lmc6061.pdf
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LM78Lxx 100-mA Fixed Output Linear Regulator
http://www.ti.com.cn/cn/lit/ds/symlink/lm78l.pdf
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8-Pin, 8-Bit CMOS Microcon troller with A/D Converter and EEPROM Data Memory
http://ww1.microchip.com/downloads/en/DeviceDoc/30561C.pdf
https://www.microchip.com/wwwproducts/en/PIC12CE673
----
ST BTA12 600C
12 A SnubberlessTM, logic level and standard Triacs
https://www.st.com/resource/en/datasheet/bta12.pdf
----
 

Thread Starter

DougPenhall

Joined Feb 22, 2019
4
So I've gone through a bunch of similar posts about broken WES51 soldering irons, and nobody seems to have the exact same issue that I'm having, or if they do, they didn't solve it.

So, I found the manual and checked he heater and thermocouple according to the manual and it seems fine. So then I checked the pins on the power supply, "With line cord plugged in and power switch on, check for 24VAC ±10% between pins #2 and #6 of tool receptacle." This test failed. There is only around 4VAC between those pins.

MODEL WESD51 ELECTRONIC SOLDERING STATION
https://www.alexwhittemore.com/wp-content/uploads/2009/07/WESD51_OI_PL.pdf
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MODEL WES51 ELECTRONIC SOLDERING STATION
https://www.scu.edu/media/school-of-engineering/pdfs/maker-lab-resources/Manual_WellerSolderStation.pdf

So, I disassembled the unit and tested the secondary winding on the power supply and it's at 28VAC. I checked the voltage across the potentiometer and it's 5.04VDC. The same points on the potentiometer feeds power pins of the PIC12C673 microcontroller.

8-Pin, 8-Bit CMOS Microcon troller with A/D Converter and EEPROM Data Memory
http://ww1.microchip.com/downloads/en/DeviceDoc/30561C.pdf

As far as I can tell the 5.04VDC is from the LM78L05ACM

LM78Lxx 100-mA Fixed Output Linear Regulator
http://www.ti.com.cn/cn/lit/ds/symlink/lm78l.pdf

So, the LM78L05ACM works and the PIC12C673 microcontroller has power.

In the corner of the circuit board there is a magnetic reed switch that is used to communicate with the microcontroller to change operating modes. I'm able to short out the reed switch to change modes and LED that's connected to the microcontroller blinks and changes from green to red and back. When it's red, I can turn the unit off and on and it's still red. When it's green, it stays green. Therefor I believe that the microcontroller is functioning properly.

So the remaining components to figure out are the LMC6061 op amp, and the BTA12 600C triac.

PRECISION CMOS SINGLE MICROPOWER OPERATIONAL AMPLIFIER
http://www.ti.com/lit/ds/symlink/lmc6061.pdf

and

ST BTA12 600C
12 A SnubberlessTM, logic level and standard Triacs
https://www.st.com/resource/en/datasheet/bta12.pdf

The 28VAC secondary winding from the transformer that powers the board goes straight to the soldering iron heater through the triac. So basically the microcontroller is supposed to somehow turn the triac off and on based on thermocouple signal. It looks like the op amp amplifies the signal from the thermocouple and sends it to the microcontroller.

So I guess the next step is to check the output of the thermocouple and the input and output of the op amp to verify that it's working. However, I believe that it is because the green LED is lit which means there should be power going to the heater. Once the soldering iron tip has reached operating temperature the LED should turn off. So the fact that there's no power coming out to heat the heater while the green LED is lit tells me that there's either the triac has failed, or the triac is not receiving the proper signal to turn it on.

Anyway, I'm having trouble understanding how the triac is supposed to work. How is it turned on? Does anyone know how I can verify that it's the triac that's failed and not some component that's supposed to be turning the triac on? I've attached some pictures so that you can see the circuits and chips. I hope someone can help me figure this out.

IMG_5942.JPG IMG_5947.JPG IMG_5951.JPG IMG_5959.JPG IMG_5986.JPG IMG_5995.JPG
 

Thread Starter

DougPenhall

Joined Feb 22, 2019
4
Replace the triac
Yeah, I agree that the triac has failed. But I'd like to prove it by testing the input to verify that it's actually being told to turn on. I'm new to triacs and they seem a bit confusing. Can they be turned on with a DC signal? or does it require an AC signal to make it turn on? Do I need to look at the input with an oscilloscope, or can I test this with a regular volt meter?
 
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