Troubleshooting Weller WES51; LED works, tool does not heat up

Thread Starter

Mike Hodges

Joined Mar 4, 2017
3
My WES51 randomly stopped working yesterday. I'm pretty good at troubleshooting, but not experienced with something like this.

The LED flashes red once when the power switch is switched on. The temp lock out LED sequence seems to work. Applying the lock out tool, the LED flashes red for 2.5 seconds then green. It always does that in that order no matter how many times you try it. I tried to reset the temp offset following the manual. Italicized lines from the manual.

I'm unclear how to "check transformer primary."
I did try With line cord plugged in and power switch on, check for 24VAC ±10% between pins #2 and #6 of tool receptacle. Assuming I'm using my multimeter correctly I didn't get a reading. I did test the fuse for continuity and it seemed fine.
I also am not sure how to Check transformer secondary for 24VAC ±10%.
The PCB looks ok, nothing obviously blown.
All wiring/solder points look ok.

I'm trying to find another pen tool to test.
I tried to Check heater resistance from pin 2 to pin 6 (see Figure 1) of the tool connector, should measure 9 - 11 ohms, I could not get a reading.


Any help/clarification would be great!
 

Dr.killjoy

Joined Apr 28, 2013
1,196
Weller has alot of problems with there pcbs failing.. I would measure the output voltage at the plug and what do you get ???
 

Reloadron

Joined Jan 15, 2015
5,667
I tried to Check heater resistance from pin 2 to pin 6 (see Figure 1) of the tool connector, should measure 9 - 11 ohms, I could not get a reading.
That would point towards an open element. You should see a steady resistance assuming a good connection.

Ron
 

dl324

Joined Mar 30, 2015
11,826
I'm unclear how to "check transformer primary."
With line cord not plugged in, measure winding resistance with your ohmmeter.
I did try With line cord plugged in and power switch on, check for 24VAC ±10% between pins #2 and #6 of tool receptacle. Assuming I'm using my multimeter correctly I didn't get a reading.
Without knowing where the 24VAC is coming from, I'd guess that the secondary was open.
I also am not sure how to Check transformer secondary for 24VAC ±10%.
Measure where the wires coming from the secondary are attached, or other similar points.
I tried to Check heater resistance from pin 2 to pin 6 (see Figure 1) of the tool connector, should measure 9 - 11 ohms, I could not get a reading.
A heater problem?

When was this iron manufactured? I've heard that Weller has gone done hill... My Weller iron from the 70's is still going strong; same tip too.
 

Dodgydave

Joined Jun 22, 2012
9,636
You won't be able to test the AC, as it will be pulsed by a Triac, you will have to open the case up and test it directly from the transformer. You can test the heater on the iron cord same pins 2,6 on Ohms should be Approx 11 ohms.

 
Last edited:

Thread Starter

Mike Hodges

Joined Mar 4, 2017
3
I don't understand it... but it works again.
I had a bit of free time, sat down to work on your suggestions. I thought I should plug it all in just to start fresh. The LED didn't flash red like it was doing previously. It just started green/heating up the pen. It reached temp and began flashing. I did a quick job I had ready and everything worked great.
I have no idea what changed. I didn't do anything. I jut checked the connections in the pen and the transformer. But I didn't change anything.
I guess for now I'm going with it. Hopefully it won't quit again soon.
Thank you for your help. I will save this thread for further use.
 
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