PS-900 soldering iron heats, but not enough to melt solder

[Dave Vandenbout]

I have a 3-year old Oki PS-900 soldering iron. I recently turned it off, switched to a different tip and turned it back on after which the tip would not heat up enough to melt solder. I switched back to the previous tip and it also failed to heat up enough to melt solder (although it was hot enough to create a first-degree burn.) I turned the iron off for the evening and it still failed to heat adequately the next day.

The only user-replaceable part on the iron is the coil assembly. Are there any simple tests I can do to verify that replacing the coil will solve the problem?

 

[Gryd3]

What type of solder are you attempting to melt, and aside from the 'Smart Heat' this thing has, do you have any control over temperature?

 

[Dave Vandenbout]

What type of solder are you attempting to melt, and aside from the 'Smart Heat' this thing has, do you have any control over temperature?

It's just Kester SN63PB37 #66/331 solder that I've been using for years.

There is no control over the temperature. The tip is heated by an oscillating EMF and the Curie point of the tip material sets the equilibrium temperature. That's why I'm confused that it would just go to some intermediate temperature. It's like it's not getting enough of the EMF to reach the Curie point.

 

[Gryd3]

I am not terribly familiar with that soldering iron, or the technology employed. I was hoping maybe that the melting point of the solder was too high.
Hopefully someone else can step in.

 

[KrisBlueNZ]

When the tip reaches the Curie point, it becomes non-magnetised, and this is detected by a switch in the barrel that cuts off the power to the heater, right? So this switch enables the heater when it detects magnetism from the tip, right? So if the tip isn't seated properly, the heater won't heat up properly. So check for dirt or obstructions that might be preventing the tip from sitting close to the switch. You could also try to dismantle the barrel and check for any visible problems.

I also have never owned this type of soldering iron, so these are just guesses based on what I would do.

 

[Dave Vandenbout]

When the tip reaches the Curie point, it becomes non-magnetised, and this is detected by a switch in the barrel that cuts off the power to the heater, right? So this switch enables the heater when it detects magnetism from the tip, right? So if the tip isn't seated properly, the heater won't heat up properly. So check for dirt or obstructions that might be preventing the tip from sitting close to the switch. You could also try to dismantle the barrel and check for any visible problems.

I also have never owned this type of soldering iron, so these are just guesses based on what I would do.

Thanks for the suggestions. I tried a seldom-used tip and it had the same problem, so it's not a problem with obstructions in the tip.

I checked the coil assembly the tips mount to. There's no dirt or corrosion on that, either.

The coil assembly is the only replaceable part of the iron (except for the removable tips). I might just spend the $20 to get a new one.

 

[Dave Vandenbout]

Just thought I'd close the loop on this problem. I bought a new coil assembly from Mouser for $22. That fixed the problem and the iron now achieves full temperature again.

 

[(*steve*)]

Excellent. It seemed to be the common factor.

Happy soldering