Q5 was listed in December 2010, and it has been more than ten years since. The mileage is not high, 145,000 kilometers, there are no major problems, there are indeed a lot of minor problems, but it is not bad. Since last year, the part J794 navigation and entertainment mainframe began to black screen from time to time, the audio cannot be turned on, and the button indicator at the gear lever does not light up.
Press the cd CD exit button, and the CD goes in and out normally.
Ask the riders in the group that they can pull the plug at the back, which can be solved after rebooting, so they begin to study how to remove the mainframe and unplug it. To be honest, it is really difficult to do it if they do not know how to disassemble it. Later, they consulted the riders in the group. A special disassembly tool is needed here, as shown in the figure:
After buying this tool, I excitedly went to the car to dismantle the main engine and found it was not easy to use. after the machine was dismantled, the tool could not be removed. Later, I consulted the rider again and took it out by a miracle. He said that he wanted to polish the head of the tool, so he polished the tool. As shown below, the red circle is used to polish the sharp corners with a file or grindstone, and the burr on the other edges should also be polished and smooth, otherwise it will affect the insertion and extraction.
After polishing, it is quite easy to disassemble and assemble, insert according to the position direction of the following picture, and open inward. The insertion position is designed to be very concealed. Look carefully at a gap. You can’t see it if you don’t pay attention to it.
After full insertion, it is shown below.
Then press and hold two circles to clamp and pull out at the same time, the main engine will come out easily, pay attention to prevent fingers from being cut by tools, it is best to wear gloves or wrap them in napkins
Host front access license
Bar code on the left side of the host
Model identification on the right side of the host
Plug harness on the back of the mainframe
The top of the above picture is the power cord, the so-called plug is to unplug the power cord restart operation. After unplugging the operation, found that the problem has not been solved, sometimes suddenly turned on, sometimes how to do is not to boot.
So I began to check the relevant online fault maintenance solutions, found that Audi mainframe black screen does not boot is a common problem, many car owners have encountered, even Mercedes-Benz and BMW have a similar situation. When I dismantled the machine, I also found that the recent temperature here is about 20 degrees. When driving for 10 minutes, I feel that the temperature inside is very high. It is judged that the mainframe works under high temperature, and the electronic products are easy to age.
The repair of this kind of fault on the Internet is usually to remove and reweld the A5 chip of the mainboard, or to replace the A5 chip. the welding of this kind of chip requires a special tool welding table, or remove the chip with a hot air gun and re-value tin solder. requires certain professional skills, belongs to chip-level maintenance, generally can not be repaired by themselves.
Driving every day, see this car machine black screen heart is always very uncomfortable, so I began to consult everywhere repair, a certain treasure fish repair price is basically 300,500 yuan, to the physical car maintenance shop asked about 500,800 yuan, 4 son directly to the program is for J794 mainframe 8000-10000 yuan, a fish on the second-hand mainframe about 2000 yuan.
Untimely in my mind, I looked at a small video and saw that there was a repair shop that repaired similar faults, only using hot air guns to repair welding, and did not do operations such as re-valuing tin, so I directly repaired the faults, so I thought I could do it. Immediately bought a second-hand digital display hot air gun, the buyer is doing electronic technology, so consult the chip repair welding related technical requirements, the general temperature is set to about 395 degrees Add solder oil to blow for 2 minutes, the advantage of buying second-hand is that you can ask for these technical details.
When I got the hot air gun, I began to disassemble the machine again. Look at the picture for details.
All unplug the appearance, unplug the plug is a slow worker can do fine work, carefully look at each bayonet, or use a small word screw to gently press the clip and then pull
Disassemble the front and back screws and add one screw at the back, a total of 17 screws, the same model, gently pry open the shell, see the optical drive on it
Gently pick up the optical drive and remove the bottom data cable to expose the hard drive
Remove the right radio head, remove the front panel data cable, and take the hard drive directly up, which is what the following picture looks like.
So far, we haven’t seen the A5 chip that we need to operate on. If you push the clip in the red circle with a screwdriver, you can gently pry up the motherboard, press the left side to tilt up first, and pay attention to the right clip to prevent it from getting stuck. The chip we want to deal with is on the back of the motherboard.
As pictured above, the chip in the red circle is the faulty A5 chip. This A5 is the display chip, not the A5cpu of the iPhone. Let’s take a closer look at the details and see what he really looks like.
The blue one is the heat conductive film, do not throw it away, if there is adhesion, gently scrape it off with a blade, you need to continue to use it
If you change the angle, the letter will be clearer.
This chip sells for 50 yuan on a treasure, but it is said that because the failure rate of this chip is relatively high, there are a lot of fakes, so we should judge carefully.
The resistors and capacitors around the chip are patch-type, and it is easy to blow these small parts off when the hot air gun is blown off, so we have to make an auxiliary tool, as you can see in the picture above.
You read it right. I deliberately drank a bottle of Coke and cut the aluminum skin into a square notch. The size of the chip is just right. When it is covered on the motherboard, it just exposes the chip, just like a surgical cloth showing a hole.
![]()
![]()
Set the temperature of the hot air gun to 395 degrees, the wind speed does not need to open too much, about 3 gears will be fine, apply some solder paste on the chip, rosin should also be OK, blow at a uniform speed for about 2 minutes, gently press the chip with a screwdriver, do not use too much force, otherwise the chip will be in trouble.
After cooling, gently wipe off the solder oil with a napkin and gently scrape off the solids on the chip with a blade.
Install the 17 screws in reverse according to the disassembly program, get on the car and install the plug.
Turn on the ignition switch and the familiar boot logo pattern begins to appear on the display screen.
The host displays the name of the song, the loudspeaker sounds normally, tests other functions, all normal
This maintenance cost 62 yuan to buy hot air gun, dismantle the machine tool iron sheet 9.8 yuan, the maintenance is all completed here. Later in the group to chat with car friends about this maintenance, the heat dissipation of this A5 chip can be enhanced by other passive heat dissipation methods. There is only a small cooling fan on this mainframe, so the cooling effect is not good. Later, when you wait for high temperature weather, you will look at the stability of the mainframe after maintenance, and add fans and other methods to enhance heat dissipation.
AlvinLondon 
7 
September 5, 2024 
