Guido Socher

Weller WESD51 blinking 888 problem



Weller Magnastat

I used to have a Weller Magnastat soldering station for many years. They were good but had one problem: the contacts to control the temperature were under dimensioned and would wear out after about a year. The fix for this was to add an extra wire from the hand tool to the station and in the station one would add a rectifier and a relay. The relay would then take the load off the Magnastat-contacts in the hand tool. With this fix the soldering station would work reliably for many years. Almost everybody I knew did retrofit a relay into their station at one point. This was obviously a systematic design flaw in the Magnastat soldering station.

The Weller WESD51

wesd51 soldering station
When digital soldering stations came up Weller introduced the WESD51 with digital temperature control. I bought such stations and about 1 year later the first WESD51 station started to show the blinking 888 in the display. The iron would then cool down. The problem did go away for a few minutes after power cycling the station.

I called Weller support when my first WESD51 station started to show blinking 888 in the display and they advised me to change the hand tool (PES51). The suggestion was that the temperature sensor in the iron might have opened up over time and loost contact to the control circuit.

Indeed the problem was gone after buying a new PES51 hand tool for the station. However after just a few month the station would again show "blinking 888" and other less used stations soon followed. The real cause of the problem must be a systematic fault somewhere else.

At this point I started to investigate the internals of station. It seems the same electrical engineer who incorrectly dimensioned the contacts of the old Magnastat was still working at Weller. This time he under-dimensioned an electrolytic capacitor on the controller board inside the station.

Fixing the Weller WESD51 blinking 888 display problem

Inside the station is a small circuit board with a PIC microcontroller a display and other components. In lower right corner is a 33uF/35V electrolytic capacitor and a diode which is used to provided a DC voltage to the microcontroller. This capacitor is too small. The value of all electrolytic capacitors drops a little bit as they age. The microcontroller gets then a too high AC component on top of the DC voltage and measures nonsense which inturn causes it to show the "error" as a blinking 888 in the display. The solution is to solder a second electrolytic capacitor in parallel. I recommend to use a 47uF or 100uF electrolytic capacitor with a voltage rating of at least 35V. Fortunately there are already 3 holes on the left next to the existing 33uF capacitor. You can solder the additional capacitor into the two upper holes. Plus is up and minus is down in the below pictures.

wesd51  controller board with additional capacitor added
wesd51 controller board with additional capacitor added

wesd51  controller board with additional capacitor added, back of the PCB
wesd51 controller board with additional capacitor added, back of the PCB

Conclusion

It's a mystery to me how a company manages to always ruin their otherwise perfect products. They are saving just a few cents on components. Fortunately it is possible in those cases to fix the design fault yourself. Happy soldering!


© Guido Socher,