Soldering a circuit together is usually a fun and rewarding job, but desoldering components on an (old) printed circuit board takes a bit more effort, especially if you want to remove that particular component in one piece for possible re-use. Many hobbyists do this with their soldering iron and desoldering wire or a tin sucker, but if you need to do this job more often you should consider buying a real desoldering station. That does not even have to be expensive, as this test of the Zhongdi ZD-915 shows.

Anyone who has ever tried to remove a 16-pin IC from an old printed circuit board without damaging the IC knows that this is not always an easy job. Especially if you regularly work on vintage equipment like pinball machines, jukeboxes and computers, then you know that old parts are often very expensive and need to be replaced carefully. For such applications, a desoldering station is an ideal tool. At least for wired parts, for SMD's often other solutions are needed to remove them (otherwise the small parts get sucked along!).

A desoldering station is an integrated combination of a soldering iron and a tin sucker, using a hollow tip on a heated hollow pin. When the pump in the soldering station is activated, air is sucked up through the tip and the hollow pin, taking the solder residues with it and ending up in a reservoir. This sounds very simple and in fact it is, but the way it is done determines to a large extent how well such a desoldering station functions and how well it still performs after a while.

What's in the box?

In the box of the ZD-915 we find a large base station with an LCD screen, a separate mains cable, a desoldering gun with two cables/hoses (one for the air suction and one for the electrical supply wires), three tips with hole diameters of 0.8, 1.0 and 1.3 mm, three needles to clean the tips and some spare filters for the collection reservoir (Figure 1).

 
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Figure 1: All the contents of the box when unpacking the ZD-915.
The last part is a glass tube with a spring in it. At the end of the tube is a metal plate with openings, behind which is a felt-like filter through which the air is sucked away (Figure 2).
 
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Figure 2: Here you can see the glass tube in which the soldering tin is collected.
A spring holds a metal plate and a felt disc in place at the back when the
tube is replaced.
This ensures that the solder that has been sucked up, remains in the tube against the filter. The box also contains a holder with cleaning sponge for the desoldering gun, which can be attached to the right-hand side of the base unit. The power of the gun is 80 W and the temperature can be set from 160...480° C. According to the description, the station is ESD-safe.

In practice

The base unit is equipped with a Euro mains socket with integrated mains fuse on the rear. The mains cable supplied can be used to connect the unit to an earthed socket. After attaching the holder to the side of the unit, we connect the two hoses of the desoldering gun to the front (the air hose via an adapter). Both are reasonably flexible and they are one metre long, which is a pleasant length to work with. The device can then be switched on using the red power switch. The display lights up with a blue backlight and shows the spot temperature on top and the set value below (Figure 3).

 
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Figure 3: The large, blue-lit display on the base station shows
the measured spot temperature at the top and the set value below.
The desired temperature can be set by means of two push buttons, a third button serves to switch between °C and F. On the right side of the display it is shown when the heating element is switched on. It takes about one minute for the desoldering iron to heat up from room temperature to 350 °C.

The first thing you notice after switching on is the rather noisy fan that is located at the back of the casing. This is not something you want to hear all the time while working, but you will most likely only turn the station on when you are really going to use it. Then, we start desoldering on an old PCB. Because the solder islands I want to practice on are not that big, I start with a temperature of 350 degrees and that seems to work quite well. I had to get used to it the first time when, after pressing the button on the desoldering gun, the vacuum pump in the station starts to operate, it makes a kind of rattling noise. Anyway, apart from that, the desoldering iron works perfectly. First heat up a soldering point with the gun for a few seconds, then press the button and the solder is gone. In this way you can remove a large multi-lead IC from a PCB. The solder remains in the glass tube and can be removed after the desoldering job. When finished, the gun can be placed back in its holder (Figure 4). Be careful to place the gun in the right way, then it will stay in place and the tip does not touch the shield..

 
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Figure 4: The holder for the desoldering gun is located together with a tray with a
with a cleaning sponge on the right-hand side of the base station.
The removal of the glass tube is not clearly described in the manual, but it is easiest if you unlock the black holder at the back and slide it backwards. Then pull the tube back as far as possible and pry up the front with the black cover. The tube is put back in the reverse order. Some spare felt discs are supplied to replace the ones in the back of the tube and in the air connection on the station if they have become dirty. I do not know if the discs are really made of felt, but the material is very similar and it is worth trying to make them yourself from a piece of felt of similar thickness.

 
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Figure 5: Removing components from a PCB is a lot easier with such a desoldering gun than with desoldering with desoldering wire or tin sucker.

Conclusion

Apart from the audible noise from the fan and pump, this Zhongdi ZD-915 is a very useful and especially an affordable desoldering station that does its job well. Cleaning is reasonably easy once you know how to remove the glass tube and put it back together again. By the way, there are many videos on YouTube showing how this ZD-915 can be made more silent with a few modifications, how the collection of solder can be improved and how the suction power can be increased. This is a real challenge for a serious electronics hobbyist!


Translation: Hans Adams