Recently, I was tinkering around with an old air conditioning circuit board which was used to control a BLDC (Brushless Direct Current) motor for the fan when I found that tracing the circuits proved to be a bit more complicated than I thought. And my intention was just to make the motor work, rather than making the controls of the inverter air conditioning with all its speed control work. Furthermore, I was quite apprehensive when testing because of the high voltages involved.

So I decided to simplify the circuits by fabricating my own. In this way, I could follow the circuits just as I had fabricated them. I planned to use the existing electronic components and rewire them in a separate circuit board.

However, when I tried to de-solder the components out, I found that the heat from the soldering iron was not sufficiently hot to melt the existing solder. A 60 W soldering iron did managed to melt some of the solder, but unfortunately the former quickly became spoiled, perhaps due to overheating of its heating element.

Aluminium curtain rails

Aluminium curtain rails

Then I read about people using hot air desoldering guns and how useful they were for desoldering, especially for surface mounted components like Integrated Circuits (IC). One interesting fact that I found was that nowadays, with modern circuit boards, there were often multiple layers to give more conducting surfaces for heat dissipation. This meant that the soldering iron that I had of about 40 W was not sufficient to bring the temperature of the solder to melting point. The heat simply dissipated away. This was very frustrating. Waiting and waiting but not able to melt the solder.

Bolt head embedded into a specially shaped head to fit the curtain rail

Bolt head embedded into a specially shaped head to fit the curtain rail

On reading further, I found that many desoldering rework stations had procedures that often had preheating prior to the actual desoldering. The circuitĀ  board to be reworked could be preheated in an oven or and a heating element could be placed underneath it. Recently, I encountered a similar problem while trying to repair a laptop recharger. IĀ  used a hair dryer as a preheating method and was successful in melting the solder. That got me thinking … A rework desoldering station would be useful for me.

Profiles of the curtain rail machined in plywood

Profiles of the curtain rail machined in plywood

So, off I went to my work bin and found some aluminium curtain rails that I had dismantled previously. I wanted to fashion them into an adjustable platform to place a circuit board for rework. The size should be large enough to place a large electronic board like a computer motherboard. The design should incorporate an easy-to-adjust way to cater for different sizes of boards.

Wooden knobs for tightening the bolts

Wooden knobs for tightening the bolts

The aluminium curtain rail was not flat, so some portions of it needed to be cut away. One side of the rail contained a groove and two curved edges. I planned to use the groove part to slide a clamping bolt and nut, but at the same time, I did not want to damage the edges of the rail when I clamped on it.

GI Gutter marked out for cutting

GI Gutter marked out for cutting

So, I designed a special piece to be attached to the bolt head so that the clamping forces on the aluminium rails would act against the curved plate faces instead of at its edges. I decided to use a soft material like plywood for this as it would be forced against the aluminium rail, which was also soft.

Almost finished heater box

Almost finished heater box

Using my movable bed cnc machine, I was able to cut the shapes out of a 12 mm plywood using a 1/8″ end mill and glued two halves of them together to form a sliding part bolt head. At first I wanted to make the height of the platform to place the circuit board adjustable, with the same concept of clamping them in position. However, after thinking about it for a while, I decided that it would be too difficult to make the structure stiff – I would need some right-angled brackets in order to make them hold their shape. Instead of legs, I decided to use two pieces of phenolic boards and bolted them to the aluminium curtain rail. In this way, I was able to create a platform to rest the circuit board, just by adjusting the width and tightening the clamping nuts.

I also fabricated some knobs out of the same 12 mm plywood and was able to use these for tightening the clamping nuts. As you can see from the video below, the soldering station was able to hold a large circuit board in place.

Incidentally, I also designed and fabricated a crude incandescent light bulb heater out of a discarded rain water gutter down-pipe to aid in my de-soldering work. It did not work as well as I thought, as the heating was too slow for my very first job, which was to replace 23 pieces of bulging capacitors from the motherboard of a computer. Luckily the soldering iron was hot enough without needing additional heating.