Weller 81 Soldering Iron Problem: No Heat and Display Cycling

[Bill Johnson]

Hello,

I have a Weller 81 soldering iron that is not heating up when turned on. The digital display on the soldering iron shows three different patterns in a repeating cycle. I would like to know what could be causing this issue. Thank you for your assistance.

[mahi]

888, <set temperature>, °C is actually the startup sequence. After that it should display the actual tip temperature and start heating. It appears as if it is stuck in a "boot loop". Maybe there's a problem with the power supply for the PIC microcontroller that causes it to restart?

[Bill Johnson]

I unplugged the soldering iron from the WSD81 soldering station. Firstly, it no longer cycles through the three pages: 1) 888 (seems to be a self-check), 2) 300 (seems to be retrieving preset values), 3) °C, 4) - - - (it cannot find the handle, so there are no temperature parameters, and it becomes unresponsive).

Secondly, even without the handle plugged in, it is still possible to set or modify the temperature preset value. When I plug in the handle, the digital display on the handle keeps flashing in the same three-page loop mentioned earlier, and I cannot set the temperature.

My preliminary conclusion is that the microcontroller is working fine. Now, I suspect that the WSD80 soldering iron may have a short circuit. When the soldering station goes through the self-check, retrieves the preset temperature, reads the current temperature, and starts heating, the short circuit causes the 24V AC voltage to drop to zero. This, in turn, results in the 12V linearly regulated voltage dropping to 5V, which supplies power to the microcontroller. The microcontroller restarts, and the temporary restoration of the 5V and 14V power supply causes the cycle to repeat.

Now, I need the pin definitions for the six pins of the Weller WSD80 soldering iron to determine if the heating element of the iron is short-circuited

[inse]

I know those failure modes on the WSP80 soldering iron: heater filament broken, thermocouple broken or cable broken.
Search for the pinout and measure both or disassemble the handle and check directly.
Never had a shorted heater up to now.

[Bill Johnson]

Thank you very much.
I disassembled the soldering iron and tested the two blue wires of the thermocouple, which measured 22 ohms. I also tested the two red wires of the heater, which measured 6 ohms. Both are normal. Now I suspect the cable.

[mahi]

If the heating element (or the cable) was shorted, I expect the triac in the WSD 81 to die quite rapidly (or a fuse pop). Since the WSD 81 doesn't "know" the triac is dead, it would simply show the tip (ambient) temperature after the boot cycle. The same would happen if the wiring to the heating element was broken (open circuit). However, that's not what happens.

My guess is that the switch-on of the soldering iron by the triac, causes an excessive ripple or brownout on the power supply of the PIC. Possibly an electrolytic capacitor has aged badly and is no longer able to keep the voltage stable enough for the microcontroller.

[eliocor]

lots of years ago I repaired one of those units replacing 1 or 2 electrolytic capacitors which got swelling

[Bill Johnson]

Thank you. I will investigate based on your analysis and provide feedback on the results

[Bill Johnson]

Thank you very much
I will also pay close attention and inspect the electrolytic capacitors

[albdoma]

Hi,
I had a similar problem. This station stuck at '°C' display.
(Background story: I had to replace the controller, but it wasn't quite the same controller on the first try...)
I found that the resonator was not working properly. (Probably the input inpedance of the new controller was so the resonator did not work. After I get the right controller,  everything works fine.)
After checking the supply voltage (and electrolytic capacitors), I would check the resonator signal.
Might be worth a try