While waiting for ebay parts to arrive for my DC load project, I thought of having a go at attempting to fix the Weller DS701E solder/desolder station which I've gotten it a while back. I have no idea when this model was produced and googling for datasheets and manual comes back with nothing.
The problem is that readings are way off and all over the place and you can see that the 7segments are actually flickering.http://www.youtube.com/watch?v=Zs80QPODk_o
My first approach was to look for visual signs of component failure and everything looks fine. So, next is to probe the temperature control board. Check out the old school pcb routing.
The board gets its power from the 12vac through 1/2 wave rectifier, filter cap, 7805 regulator and another filter cap.
Initially, the voltage measured at the regulator was 7v at the input and 4.2v at the output. The filter cap was quite warm.
Tested the cap ESR was 0.7ohms and not shorted. My capacitor meter was only limited to 200uF max. So I concluded that the cap has lost its capacitance over time.
Replaced them with what ever I have in my junk bin and it works like a charm. Did some quick calibration with a thermal probe.
I've decided to replaced all the caps just in case. Im actually surprised that there are very few ICs in one of these.
Phillips caps. When was the last time you heard of them? I know they were acquired by some company, Vishay was it?
An overall shot of the internal. The transformer is rated at 24v 280va. Which took up most of the weight.
I've also took the opportunity to strip the old paint with a wire brush. Some fine sanding and elbow grease and finally a couple of clear coat. Tried to create the brush alu effect. Unfortunately, the desolder tool wasn't working, it dint get hot but the pump works fine though. Looks like another job for another time.