Weller EC2100M Soldering Station

[brian_mk]

I have owned my Weller EC2100M for some years.
It has worked reliably until a couple of weeks ago when it began to behave intermittently at start up.

Sometimes at switch on, the iron fails to heat up at all. Power cycling or disconnecting & reconnecting the iron seems to get it working again.
Sometimes at start up, it displays the maximum temperature (over 500deg) for several seconds, then the temperature display drops down, undershoots and overshoots several times until it reaches the set point.
Once it's stable at the set point, it settles down and seems to behave correctly.

I've checked the obvious things:-

I disconnected the iron and measured the heater and thermocouple temp sensor resistance. I get 28 Ohms for one and 12 Ohms for other.
The resistance reading is stable even if I wiggle the cable around, so I don't think it's a broken wire.

I have cleaned the pins and sockets in the connecting plug with a sliver of fine emery paper. I also tried contact cleaner.

I have opened up the base unit and cleaned and reseated the internal PCB connector.
I could find no evidence of bad solder connections.

While the base unit was open, I checked the heater and thermocouple temp sensor resistance all the way through the cable, plug and header to the PCB while jiggling the cable and connectors. I could find no evidence of an intermittent contact.

Tweaking the temperature setting when the iron is in the initial unstable state doesn't seem to help, so I don't think it's an intermittent pot.

I have run out of ideas.

[brian_mk]

I have uploaded a video clip that illustrates the problem:-

http://www.briank.plus.com/images/MVI_1214.MOV

[thm_w]

Did you look at the circuit board inside the unit itself, any bulging or old caps?

Heater will eventually die but don't know if that is the case here.

https://maker.pro/forums/threads/weller-soldering-station-ec2100m.252220/
https://www.electrondepot.com/repair/need-weller-ec2001-soldering-station-info-48213-.htm

[floobydust]

It acts like an thermocouple RTD to heater short occurring when the element has heated up, so this acts intermittently. Check resistance between TC RTD and heater. You can check for big voltage drop across the PTC fuse if it is activating.
Other failures can be an open thermocouple RTD or heater ground-fault occurring. Check resistance between TC RTD and heater and ground.

The controller likely shares a lot with the WES50/WES51/PES51 family {no}. Also the two electrolytic caps on the controller board are known to age.
A lot more in thread https://www.eevblog.com/forum/repair/weller-soldering-iron-wes51/ for the WES51 but it seemed to be a new heater was needed.

edit: it's an 20Ω platinum RTD for the temperature sensor in the EC234, not a K thermocouple like in WES51/PES51 heater/sensor assy PES201.

[brian_mk]

It acts like an thermocouple to heater short occurring when the element has heated up, so this acts intermittently. Check resistance between TC and heater. You can check for big voltage drop across the PTC fuse if it is activating.
Other failures can be an open thermocouple or heater ground-fault occurring. Check resistance between TC and heater and ground.

The controller likely shares a lot with the WES50/WES51/PES51 family. Also the two electrolytic caps on the controller board are known to age.
A lot more in thread https://www.eevblog.com/forum/repair/weller-soldering-iron-wes51/ for the WES51 but it seemed to be a new heater was needed.

Thanks for the suggestions - it prompted me to re-check the connections and resistance of the heater and thermocouple temp sensor.
This time I unscrewed and removed barrel outer sleeve.
Instead of the 28 Ohms I measured previously, it was about 48 Ohms. When I tapped the barrel, the resistance changed. The reading was jumping all over the place.
It looks like this is probably the culprit. Is it the heater or the thermocouple temp sensor?

BTW - the video clip I uploaded has now been removed because it exceeded my free webspace allowance.

[brian_mk]

I took the iron apart and removed the thermocouple/ temp sensor assembly.
I measured a stable reading of 28 Ohms at room temperature.
I used another iron to heat the sensor. The resistance increased to about 44 Ohms. Is that sensible?
The readings were steady and not fluctuating.
It's a bit unclear at the moment if the thermocouple temp sensor is faulty/intermittent.

[brian_mk]

I reasembled the iron and it seems to be working normally at the moment.
A new sensor assembly costs around 70 GBP so I need to be sure the old one is faulty before shelling out on a replacement.

[floobydust]

Heating element EC234 has a platinum RTD typ. 20Ω at 0°C, gives RTD roughly 22Ω at 25°C and 46Ω at 350°C/662°F. Heater is 13.0Ω
No data on EC208 could I find- but it is likely similar? No idea when Weller used a thermocouple instead.

You may have fixed a poor connection to the temp sensor. If there is further trouble, it might be a problem inside the heater or next I would replace the electrolytic capacitors on the controller board.
https://www.eevblog.com/forum/repair/weller-station-repair-advice-weird-symptoms-for-non-heating-iron

[brian_mk]

Apologies for referring to the temp sensor as a thermocouple. I got that completely wrong.
As pointed out by floobydust it actually uses an RTD.
The part number for the temp sensor assembly in my iron is EC229A.
It looks like they are still obtainable from Amazon UK (made in Mexico).

https://www.amazon.co.uk/Weller-EC229A-Sensor-Ec1201A-Black/dp/B000B61J6C

The iron is still working at the moment. If it goes wrong again I will order a replacement.

[brian_mk]

Ther iron has been misbehaving again lately. Same issue as before.

I took the base unit apart again.
This time I desoldered the three SMD electrolytics and checked them using a bridge. They all appear to be ok: values within tolerance and reasonable ESR.
I checked the sensor and heating element resistances - both look ok when cold.
I checked the contact resistances through the front panel connecting plug and the PCB connector - all appeared good.
After reassembly it appears to be working normally again.

I can only think the problem may be an intermittent temp sensor.
Unfortunately the EC229A is no longer available from Amazon uk.

Inside the base unit is a PIC processor plus a serial linked EEPROM and a 12 bit ADC.
Any idea what the EEPROM is used for? Temperature calibration data?