Fujitsu Mini Split A/C Circuit Board Not Turning On Test

In this video, we dive into the world of HVAC troubleshooting as we tackle a common issue with Fujitsu Mini Split air conditioning units. If you’re experiencing problems with your A/C circuit board not turning on, you’ve come to the right place! Join us as we guide you through the step-by-step process of diagnosing and testing the circuit board in your Fujitsu Mini Split A/C unit. We’ll cover the essential tools you’ll need and provide detailed instructions to help you identify the root cause of the problem. Throughout the video, we’ll share valuable insights and expert tips to ensure you have a comprehensive understanding of the circuit board’s functionality. We’ll explore common issues that may prevent the circuit board from powering on, such as faulty wiring, blown fuses, or damaged components. By the end of this video, you’ll have the knowledge and confidence to troubleshoot your Fujitsu Mini Split A/C circuit board effectively. Don’t let a malfunctioning circuit board leave you in the heat! Join us and get your A/C unit back up and running quickly.

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#circuit #ac #repair #fujitsu #motherboard #pcb #electronics #airconditioner

This is a Fujitsu mini-split AC motherboard. It seems to be fine physically, but it is not turning on. I have passed electricity through it. I am going to check how many voltages are passing through   its Bridge rectifiers. The pins in the center are for the AC voltages I will check the DC voltages first

302 DC volts are passing through the DC pins, on the second rectifier, 202 DC volts are passed   through the DC pins, this means the electricity is passing fine through the rectifier, often if   the IPM is bad. The circuit board does not turn on, and we have no idea which component is bad 

I will connect the positive to the positive and the negative to the negative pin of a multimeter   with the IPM. 302 DC volts are passing on the positive pin. 11.56 volts are at the W pin. The next pin also has the same voltages. 11.57 volts is also passing on the last pin. This means that  

The IPM is fine, a fuse is installed in the SMPS circuit, through this fuse we will check if this   switching IC is working properly or not because 11 volts are coming at IPM. This means that the   SMPS circuit must be working and that is why 11  volts are passing on the IPM I will check 

Pin number two and three of the IC with a fuse to see how many voltages are passing through here   there are 303 DC volts here, pin number eight of this switching IC is the drain that is it is the  

Output pin of this IC. No voltages are passing on this pin. I accidentally touched the probe with the   other pin of the IC, and see that the switching IC has turned black from this point, so right here  It is important that we change this switching IC. I would clean the switching IC before desoldering it. 

Because there is a thin layer of silicon on the circuit board, which makes desoldering a bit difficult To desolder the IC, first, I am adding solder to its pins with the help of soldering wire. this will desolder it easily now through the IC holder, I will pull this IC out of the circuit board

Getting this IC out is getting a bit tricky, so a good technique for this is I’ll hold the IC holder pressed into the IC, I won’t leave the IC holder, and let’s rotate the circuit. Now I will  

Gently heat the IC pins with a soldering iron and look the pins are starting to go out. We have taken   the IC out this way, so it is a good technique. This is the old IC with white writing on it which is top243PN On the left is the new switching IC.

After replacing the IC I have now powered the circuit board    let’s check the voltages on the switching IC again, I will connect one probe of the multimeter  to the fuse and the other pin to the number two and three pins of the IC, the multimeter  

Is showing us 320 DC volts on these pins. The voltages are slightly higher on these pins than before which is fine. So, is this switching I see switching because we can’t directly   see the voltages at pin number eight through the multimeter. We need an oscilloscope for that  

I will attach one multimeter probe to the ground pin of this capacitor and I will check voltages   by connecting the other probe with diode number Fifty-five.15.39 volts, the multimeter is showing here

This means that this IC is switching on, also let’s check the next part of the circuit, whether the voltages are correct here or not. So here is another diode mounted, where the multimeter is showing 15 volts And the cathode of this diode has 14.74 volts, there is a slight voltage drop

A zener diode is mounted next to it. This is an 8.2-volt zener diode mounted in Reverse bias.  That means that any number of volts greater than 8 is passing behind so they will cross from here to the cathode 6.45 volts is coming to this pin, on this diode we are getting 5.8 volts so we’re getting  

5 volts at pin number four of the IC, which is its feedback pin. that means it is working properly.   Pin number one of this IC is for overcurrent. For some reason, if the voltages are correct and the current   is getting high, then this pin turns off the entire circuit board. The four resistors mounted here are  

Half megaohms resistors, So 2.6 volts are passing across these resistors which means that PIN number one   is also perfectly fine because if the current increases here the voltages also increase, if the   current increases at pin number one of the IC the entire IC will shut down eventually turning  

Off the entire circuit board. Now I will check the voltages from the other side of the circuit board I am checking capacitor number 66 to see how many volts it has. 8.8 volts are across the capacitor which is fine, I am going to check the voltages across capacitor number 65.

13.9 volts are on this capacitor and it should be 12 volts on this capacitor, these are a bit High I will tell   you further if these high voltages cause damage or not. Now next voltages I will check on the capacitor   Number 69, this capacitor has negative voltages so minus 9.11 volts coming in here, which is fine  

After that, I would check for 15 volts, probably on  the capacitor, on capacitor number 64, so 15 volts   are coming across this capacitor, which means that all the required voltages on this circuit we need   are exactly right. Now I will check the voltage on the 7805 IC. The multimeter is showing 5 volts at  

Its output pin and this IC is showing 8 volts at its input pin. This means that the SMPS is working fine  But the motherboard is not turning on at all. Normally when the circuit board is fine   the microcontroller checks all the inputs of the circuit board and it happens so fast that we don’t  

Even know when it happened, and then it starts its next functions. Now, I will measure the DC link   of this circuit board. Ao to check this, I have to connect one probe of a multimeter to the ground.  

So, the ground is also present on this soldering pad apart from this, we can also take the ground from   another point, so for now, I will take the ground from here so on this resistor I will check what   the voltages are. So, about 3 volts here is what the multimeter is telling us, which is perfectly fine.

And we wanted the same number of volts on this resistor as the currents and voltages   Increase here so well on this resistor this lets the microcontroller know that all functions are   working properly, the DC link voltages are fine but are they reaching the microcontroller or not so  

We will check that. So, on pin number eight of the microcontroller, I will check this. If you work on   a microcontroller do it very carefully because if the two pins of the microcontroller are connected   while checking it, then this microcontroller will be dead. I have connected the probe to pin 8 of the microcontroller 

It is getting a bit difficult because the pins of the microcontroller are very close 3.1 volts is present on this pin 8 of the microcontroller which means that the DC link   voltages are reaching the microcontroller. DC link voltages are generated later but AC link voltages  

Are generated earlier. To check the AC link you can see that there are two resistors and these   are the other two resistors attached. The first two resistors are connected with phase and the second   two resistors are connected to the neutral in the circuit board. let me show you its voltages  

I set the multimeter to AC volts, I would place the red probe at the beginning of the first two resistor pins and so I’ll put the black probe at the beginning of the other two resistor pins 224 Ac Volts are available here. All these resistors have a value of 194 kiloohms so the voltages across  

Their opposite pins are divided. So let’s check the voltage on these pins. So about 111 volts   are present here on these pins, which are half. So let’s check the output voltages at the last pins   of these resistors, so at the output we are getting 2.2 volts. We can also check their voltages with DC ground 

I will set the multimeter to DC voltages. I will connect one probe of the multimeter to the ground. so we are getting 1.1 DC volts at the output pin of the resistor but here it is better  

To check the voltages in AC volts. The 2.2 volts ac we were getting at the output of AC link resistors   goes to these two resistors both of these have a resistance of 22 Kilo-ohms. These voltages are further  

Fed into this IC at PIN number 9 and 10. Number nine is inverting and 10 is the non-inverting PIN of this IC  This IC is a ground sense amplifier which is a four Channel IC and through which   this IC is functioning. This IC requires voltages to operate so the necessary Volts for this IC

To operate are positive and negative, I’m talking about negative voltages not ground, so let’s see   how many negative voltages. I am taking the ground here to check out these negative voltages.  At Pin 11 of the operational amplifier we get Negative voltages, pin number 11 of this IC is connected  

To this capacitor, you can see negative 9.11 volts are shown on the multimeter and it’s important voltages for that   Positive voltages are then required the main Supply is on pin number four of the IC, there are 15.39 Voltages coming on this pin and these voltages are essential for the operation of this I-C.

Without these voltages the operational amplifier will not work. Now let’s talk about the outputs of this I-C, the input is on the pin number nine and ten of this IC which is channel number 3    So, it’s output is at pin number eight of the IC

It goes from pin 8 of the IC to channel number two in the IC in which the input pins are the 5 and 6. The output of channel number two goes to pin number seven in this IC..

At the seventh pin, let’s check the voltages. – 1.7 volts are on this pin, so I will put the second probe of the multimeter on   this pin of IC and see if it ends up negative voltage value or not. Now after replacing the  

Probes it is showing a positive 1.7 volts on this IC, These same voltages will move forward towards   the IC operational channel number one, this would increase the amplitude of the voltages. Let’s check   how much voltages do we get on pin number one of the IC. 3.4 DC volts is what we are getting  

On this pin of the IC as output. These voltages will move further to the microcontroller pin number seven This is the PIN number seven of the microcontroller. 3.4 volts are passing on this pin   of the microcontroller, which means these input voltages are reaching the microcontroller.   

These were the positive voltages, but it need the ground to operate, these 3 volts also flow to this ground   sense as well. Its number is ba293f. This IC has eight pins, the voltages go to channel number one   of this ground sense IC. The one number pin of this IC is the output. The output of channel  

Number two is pin number 7. The channel number four with pin 14 has also been grounded, so I will   check the output on the ground sense IC. I will take the ground where we had taken it before.

And this is the PIN where we will get output voltages on this IC. It does not give any output voltages.  If we check ground with the ground it’s not showing the voltages this means that this is the ground pin of  

The IC, I will have to check it with any positive voltages. I will attach the red probe here with the   Positive voltage pad, and let’s check the voltages again. 302 volts are passing through this pin.  Which means we have attached the correct polarity. Now  this ground is reached towards the microcontroller  

Pin 36, so let’s check the ground voltages moving through the microcontroller. The multimeter is   showing 15 volts and if I change this probe with the other probe, it is showing 303 volts here. This means that these input voltages are passing fine through the microcontroller. Now, I will  

Tell you how this microcontroller controls these voltages. I have installed this voltage regulator here.  First, we will check it at 220 voltages so for that, I will take the voltage to 220, so let’s   check the voltages on pin 36 and pin 7 of the microcontroller. 3.4 Vols we are getting here on  

These pins, so now I will reduce those voltages a bit because I have experienced on this fujitsu   circuit boards that it works up to 190 volts. Its circuit board does not operate at voltages below 190 VAC The operational amplifier slightly reduces the amplitude of the voltages. 2.9 volts are now  

On these pins. The microcontroller knows that the voltages have been decreased and now I will lower   the voltages further to 175 volts. Now let’s check the voltages on these pins. The voltages   have dropped further. At 2.7 volts it will stop the circuit board from from working and will  

Give us a low voltage error, and so I will turn the voltages up. I turn it all the way up. The capacity   of my voltage regulator is 260 volts. I set it to 260 volts, so now I check its voltages again. 

And see if the voltages are high or low, so you can see that the multimeter is showing us 4 volts   so this means that when the voltages go above 4 volts, it will shut down the system and show the  

High voltage error. In this way, the AC voltage is controlled by a microcontroller with the help of   this operational amplifier. This voltage detector is installed here, so let’s check its voltages.  The pin of this IC on the right side is not connected, The pin on the left side is its ground. The bottom  

Pin on the right has an input voltage of 5 volts, and the left pin on the bottom is the output, so first   I will check how many voltages are coming here. From here, I will take the ground and set the  

Multimeter on DC voltages, so now I will take a look at its input voltages where I put this second probe Is its input, Trace. Here we are getting 5 volts, Now if I check the voltages on the second pin  

We are getting 5 volts here as well. After that, I will now check the voltages at Pin 19   of the microcontroller, which is passing here. 5 volts are present here. The voltage detector voltages are also fine.  I will now test the microcontroller’s most important voltages that run this microcontroller.  

Three pins in this microcontroller are vss called ground and three pins are the important positive voltages. Which are the 5 volts, if any one of them is missing the microcontroller will not work.   The 14-number pin of the microcontroller is the vss, which means it is attached to the ground.   

This is the 14-number pin of the microcontroller, and it  is attached here with this point. With it the next   pin is the number 11. You can see this print here, and when I follow this print, It is attached with  

The 11 and 12 number pins of the microcontroller. Both of these pins have the important voltages of   this microcontroller, so I will check the voltages within this point. Fix 5 volts are being reached here. This means the important voltages in two of the pins of the microcontroller are perfect.  

The next pin is the 24 pin, which is the ground pin, and this is the point of the pin. I will place the   second Probe on the point of pin number 56, 5 volts are also present across these pins. I am going to  

Check this capacitor. This capacitor is used to stabilize the voltages of the microcontroller from   any fluctuations. let’s check what the potential difference between capacitors is. 3.3 volts are   passing across this capacitor. This means that the voltages that make the microcontroller work   in this circuit board are also fine. Finally, I will test the current detection circuit.

You can see here that two operational amplifiers are mounted. One is this and the other is at the back of it. These two operational amplifiers detect the current and tell the microcontroller how   much current is flowing in the circuit. I have already checked the resistances around these  

Operational amplifiers. First of all, I will check pin number eight of this operational amplifier to   see how many voltages are present here. 15.3 volts are passing through this pin, which is fine. I will   now check the voltages on its pin number four, The voltages here are -9 volts, which means that  

It has been driven through negative voltages. The other operational amplifier is the same as this   one with 15 volts on the number eight-pin and minus 9 volts on pin number four, the output of   this IC is really important, pin number one is the output of this IC, so let’s check it, we will take  

The ground from the old place, there are minor voltages here because as the current increases   so do the voltages, and now you can see here that 2.6 milli-volts are coming up here, which is absolutely fine Now, in the same way, let’s check the other IC too. Both should have the same voltages. 2.6 milli-volts  

Are here as well. Now, the voltages of this current detection circuits are passed into   the microcontroller and at its pin number three. let’s check if these voltages are reaching this microcontroller   Yes, these voltages are reaching here, these voltages fluctuate a bit but are fine.  

As the current increases, the voltages in the circuit also increases and the microcontroller   Knows how many amperes are flowing in the circuit. This is another Fujitsu air conditioner PCB that I Repaired.   In this clip, I tested the output voltages of the current detection IC that I will show you  

While the compressor is running, the compressor has started and we see how many voltages are   appearing at its output, the voltages have started to increase. The voltages have increased to 397 milli-volts. Now I will check some more voltages and after that, we will come to a conclusion about  

This circuit, so when all the inputs go to this microcontroller first, it turns on this relay and   passes voltages to this communication IC, so in this circuit board the relay is not turning on   and neither is this communication IC. So now I will check the outputs of this microcontroller. 

To see whether it is sending it to this Darlington array or not, the customer sent me a video in which   the AC timer light blinks twice which means that this is a communication problem. The PIN number 31  

And 32 of the microcontroller, the 31 number turns on this relay, and the 32 number pin turns on this   communication IC, this is a uln2003 IC, and the  31 number pin of the microcontroller is connected   with the five-number pin of this Darlington array, so let’s check the voltages on the five-number  

Pin of this IC. 7.1 Milli-volts are passing through this pin which is nothing. This pin should have 4 to 5 volts   This means the microcontroller is not turning on the output. The next pin is 32 which is attached   to the Darlington array pin number two, so let’s check the voltages here on this pin. 7.2 milli-volts

Are passing through this pin as well, This means that the microcontroller cannot pass output to the   relay and the communication IC due to which the problem is caused. The rest of the components in   this circuit are working but the microcontroller in spite of the proper input voltages is dead at  

Its output. This circuit board can’t be repaired and I have no other microcontroller that I could   replace with this bad one. You can support the channel on Patreon. Link in the description.  Click on the left or right thumbnail to watch our next videos and subscribe, thank you.