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
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, back of the PCB
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!