How an IT specialist from Liebherr in Holland repaired

Each country has its own peculiarities of national life, which may cause misunderstanding among immigrants. In Holland, local architecture turned out to be such a feature for us. No, not the one about pediments and entablatures, in this regard everything is ok, but the practical part of it is the size and layout of housing, especially rented ones. In a few words, these engineering solutions can be described as “narrow, uncomfortable and nowhere to live.” A fairly typical phenomenon for a rental apartment, of which we are happy tenants, is a miniature under-counter refrigerator without a freezer compartment. Locals, as a rule, fill it with beer in cans (although what is the correct name for an aluminum can?) and have a great time in front of the big screen with football. And for us, look, give us housekeeping… some kind of game, and that’s all. Considering the lack of space and the difficulties of potential transportation to another place of residence (hello, hello to the Dutch stairs), we hesitated for a long time to buy ourselves a normal refrigerator. But then He appeared to us at the flea market – an old and rusty Liebherr GP1466, low freezer. With a price of 'only' 160 euros, for unknown reasons, this seemed like a super offer to me. It probably just seemed like it, I realized later. In my defense, I can only say two things. Firstly, its dimensions were at the same time minimally reasonable in terms of practical usefulness and maximum in the sense of being able to climb up those very stairs. Secondly, in our homeland Liebherr has worked for 30 years, and will continue to work.

In general, patience ran out, “something had to be done,” and we, with the help of Croatian friends, rolled up and dragged this miracle of technology to the second floor, which the Dutch call the first. When we turned it on, after letting it sit for a couple of hours, the compressor rustled as expected and began to cool. Tired but happy, we went to Ikea to buy frozen meatballs, because now we have somewhere to put them! But upon our return, the number -3 was still flashing on the display, even though a good 6 hours had already passed. The water in the glass, however, froze quickly, which gave me some ideas. The next morning the situation had not changed and it was decided to get hold of a thermometer. The thermometer showed a brisk -25 inside, which made me very happy, because this meant that the compressor and refrigerant were in order, and the problem was in the thermostat or sensor. And this “you’re a programmer” thing will somehow be sorted out.

The thermostat module was easy to remove:

But that was all: the wires went far into the foam, the top cover turned out to be tightly glued, and there were no panels visible in the camera behind which the sensor could be hidden.

At first, these circumstances did not upset me too much, because one of the problems became obvious immediately and it affected exclusively the thermostat. As usual when repairing electronics, I began to measure the supply voltage and noticed that it sags in time with the blinking number on the display. “Yeah! – thought Stirlitz. This thermostat uses the simplest circuit capacitive power supply. In such a scheme impedance The capacitor plays the role, to put it simply, of high resistance (alternating current), at which the difference between 220 at the input and 5V at the output drops. This particular device uses the so-called self-healing class capacitor X2. Such “self-healing” capacitors are characterized by their special method of “silent death”: instead of exploding with sparks, their plates burn off piece by piece during overvoltages, leaving no visible marks on the outside. The only thing that changes in this process is the capacitance of the capacitor; it drops.

When I unsoldered and measured the capacitance of the capacitor, it turned out that we were dealing with exactly this situation. At a nominal value of 0.68 µF the measured value was only 0.19 µF.

Here I could wait until Monday and look for a new capacitor in radio products, but I like to solve problems, being content with what came to hand. And I came across one found on ~~trash heap~~ there is a printer on the street (maybe even a working one, but there was no time to bother with it). But I guessed that the printer had a power supply, and that there might be a similar capacitor lying around in the power supply. And he was there!

Having connected a “sort of new” condenser in parallel with the original one, we managed to reach almost the nominal parameters of the circuit, but… This still did not help – the display still blinked with the number -3.
So it was probably the sensor, I thought. The sensor in these refrigerators is NTC thermistor. This is a tricky resistor whose resistance increases as the temperature decreases. I even managed to find table of resistance versus temperature for Liebherr sensors. But bad luck, measuring the sensor with a multimeter showed that the resistance was quite within the required range.

So I had to tinker with the debug further. First I wanted to investigate what numbers the thermostat shows depending on the resistance connected to it. These experiments were not productive. It turned out that the display shows not the current value, but something like an hourly average. But in the process, I discovered that the thermistor behaves nonlinearly: when operating current passes through it, its resistance drops compared to that measured by the multimeter. This is such an insidious bug – when I tried to catch it, I hid. Most likely, the nonlinear behavior was caused by moisture that somehow got inside the sensor.

Well, it is now clear that I need a new replacement sensor. Liebherr has it on his website page with diagram and list of components. However, there was not much benefit from either this page or the correspondence with support. In fact, all I could find out was that a new sensor costs 80 € and in general I’m unlikely to get it so easily, because the model has been discontinued for a long time, well, you understand… In general, I considered paying half the price of a freezer for a thermistor not kosher and I finally got to the radio goods to buy the most ordinary 10k thermistor for pennies.

Now the problem was to get to the original sensor. The wires, as I already said, went into the foam and it was also not possible to disassemble any of the body elements. Fortunately, the good guys with Italian Forum shared proprietary instructions for replacing the sensor.

In accordance with the instructions, it was necessary to climb inside and use a knife to cut a window in the plastic body of the camera according to ~~purchased tickets~~ drawing. If it weren't for the Italians, I would have guessed it in two jesters.

All that was left was to cut the wire and solder a new thermistor.

If you slip cut strips of hot-melt adhesive under the heat shrink, then after heating it reliably seals the entire structure, thereby preventing possible tricks with moisture ingress. Now you can cover this whole shame back with the broken lid and carry out tests.

Ta-daam! Go!

Naturally, the calibration has run away, but for the range of -10..-20 that interests me, the difference is several degrees, which suits me quite well. In case anyone is interested, used thermistor here.

This may not be the most “neat” renovation, but we have already celebrated the holiday of the first ice cream, and most importantly, there is no longer a need to take out this freezer and bring in some other one to replace it. And Liebherr was saved from the landfill, which seems to be a plus for environmental karma.

My original article on Medium here. Possible in this same blog look at other articles that I have not yet translated.