10.09.2023
A bug from a car's FM modulator. Typical faults of an FM modulator Self-repair of an FM modulator
After the video, many users from different sites, as well as YouTube subscribers, asked for instructions on how to assemble a bug from an FM modulator. FM modulator has become quite a popular device recently. It is designed to transcribe audio tracks and transmit over a radio channel. Range up to 10 meters.
In order to assemble a bug from a modulator, you don’t need any special skills or knowledge in radio electronics, just the basic knowledge of a novice radio amateur. We disassemble the FM modulator and throw out the housing. The filling is powered by 5 Volts, voltage from on-board network the car arrives at linear stabilizer the voltage at the output of which we get the indicated 5 Volts, it is this voltage that powers the digital part of the modulator.
Any modulator consists of a small processor (in our case it is not needed, but it is impossible to separate it from the main board) and a transmitter. The main advantage of such a bug is that the circuit has quartz stabilization, therefore the transmitted signal is of very high quality and there is no frequency slope observed here. 
The circuit can be powered even from one battery mobile phone with a voltage of 3.7 Volts. On the main board we can see the transmitter chip. 
We turn on the radio transmitter and tune the modulator to any frequency; tune the receiver itself to this frequency. Next, take a thin and sharp metal object (necessarily bare), for example a needle, and one by one touch all the pins of the microcircuit with the tip of the needle. When we touch some pins, we observe distortion in the radio receiver. 
We choose the output that responds to touches more than the others, that is, the distortion in the receiver is louder than in the case of the others. Directly to this pin we connect (solder) a non-polar capacitor (ceramic or film, it doesn’t matter) a capacitor with a capacity of 0.1 µF.
We submit for free withdrawal beep, when connecting an electret microphone, we get a radio transmitter.
FM modulator or transmitter is a cool thing. Convenient, very convenient, downloaded a lot of songs and rewrote them, tired of them. You can also all listen to music from one modulator together. We have one in the garage bay, it’s always on, so everyone is tuned in to it. It looks different; I have this modulator.
They all have the same functions. Various versions appearance modulator and its memory, some don’t have it, and you have to insert an external flash drive.
Okay, let's get to the point. I did not rejoice for long at the flawless operation of the modulator. When it broke, an opinion arose like Chinese garbage. I threw it away on the shelf and somehow managed without it.
I recently got around to the modulator. I took it apart: the breakdown turned out to be nonsense. There was a fuse in the modulator plug, which is inserted into the cigarette lighter socket. Burnt!
There was no such thing at hand.
We take stranded copper wire. We select two cores from it. I have them with a diameter of approximately 0.2 mm. Some might say that this is too much, but is the fuse still blown? And it was 250V 0.25A, which is also not small.
We twist the two veins into one rope.
First we tie one fuse contact, then the other.
We secure our jumper with electrical tape or paper adhesive tape. It is necessary that the contacts remain bare.
FM modulator or transmitter is a cool thing. Convenient, very convenient, downloaded a lot of songs and rewrote them, tired of them. You can also all listen to music from one modulator together. We have one in the garage bay, it’s always on, so everyone is tuned in to it. It looks different; I have this modulator.
They all have the same functions. The appearance of the modulator and its memory vary; some do not have it, and you have to insert an external flash drive.
Okay, let's get to the point. I did not rejoice for long at the flawless operation of the modulator. When it broke, an opinion arose like Chinese garbage. I threw it away on the shelf and somehow managed without it.
I recently got around to the modulator. I took it apart: the breakdown turned out to be nonsense. There was a fuse in the modulator plug, which is inserted into the cigarette lighter socket. Burnt!
There was no such thing at hand.
We take stranded copper wire. We select two cores from it. I have them with a diameter of approximately 0.2 mm. Some might say that this is too much, but is the fuse still blown? And it was 250V 0.25A, which is also not small.
We twist the two veins into one rope.
First we tie one fuse contact, then the other.
We secure our jumper with electrical tape or paper adhesive tape. It is necessary that the contacts remain bare.
Hello, dear friends!
I would like to talk about a compact FM transmitter for connecting to audio devices via a 3.5 mm audio jack. The transmitter allows you to broadcast an audio signal over radio frequencies in the range from 87.5 to 108.0 Mhz. I ordered it for a friend, keeping in mind the price and attractive design (he asked for an inexpensive one so he could listen to audiobooks in the car). Before giving it to him, I took it apart a little and tested it. The review contains detailed photographs and impressions of use.
Delivery within 19 days, packed in a bubble wrap bag, contents undamaged.
IN complete the device itself and a micro USB cable for charging the battery, cable length 30 cm. The design of the transmitter is simple and concise, stylized as Apple products. 
During charging, the charge level is displayed (4 gradations): 
The transmitter can be connected to any 3.5mm headphone output: phone, laptop, mp3 player, computer, etc. 
Elementary connection and setup:
1) Turn on the device with the on\off slider
2) Set the desired transmission frequency, for example 87.5 Mhz
3) Apply audio signal from the source
4) Tune in on the receiver (another phone, radio in the car, etc.) to the frequency 87.5 Mhz
5) Experimentally adjust the sound level at the receiver and source (to minimize radio interference)
The case has latches and can be easily disassembled using a plastic card: 
The microcircuit has no markings, just in the form of a drop. The battery is also nameless. 
The backlight is bright enough, the numbers are easy to see. After a few seconds it goes out on its own. 
The battery lasts for 5-6 hours of continuous operation. The estimated battery capacity is 180 mAh.
The quality of audio signal transmission is average for this class of devices. In a quiet room at a distance of 10 m from the source, weak radio interference can be discerned in the headphones. To check, I transmitted an audio signal from phone to phone (the antenna in this case was the phone’s headset).
In principle, this interference is barely noticeable; I removed it by adjusting the volume of the audio signal on the transmitter and receiver. In a car this interference is not noticeable.
Purchase:
After purchasing and receiving the device, I learned that there are transmitters with a similar design, but with more solid characteristics.
For example, this one is more expensive and with best characteristics model
As far as I can tell, on at the moment, This best option, which can be ordered on the Internet, if you start from a specific design.
Conclusion: The universal FM transmitter has been tested and found operational, all functions are normal. During testing, I did not find any anomalous behavior.
Pros:
1. Nice, laconic design
2. Versatility and ease of use
3. Autonomy (5-6 hours)
4. Compact size
5. Good quality of audio signal transmission
6. Display backlight
7. The transmitter can work while charging
Cons:
1. No instructions
2. Microcircuit on the board without markings
3. No information about battery capacity
Thank you for your attention, happy online shopping everyone!
P.S.
Regarding stereo:
The number of wires entering the plastic seal of the audio plug and the designation on the board indirectly hints to us that there is stereo. Since the main chip is not signed and it is impossible to look at the specifications for it, it is difficult to say anything definite about this.
It would be interesting if the owners of such devices, of which there are many, judging by the comments, posted photos of disassembly and it would be possible to compare more objectively 
I’ll add a useful comment from a Muskovian with the nickname lockeron:
“It’s a good transmitter, I bought one myself. You can watch my video review of it:
I'm planning to buy +38 Add to favorites I liked the review +22 +49
Typical malfunctions of FM modulators (transmitters) can be divided into 3 types. I will talk in detail about only one, since the other two in 50% of cases lead to the complete unsuitability of the device!
The first type of malfunction is the failure of the stabilizer chip. Figure 1 shows the modulator itself in disassembled form.
FIGURE 1 (click to view)
Figure 2 shows a stabilizer board with a 7805 chip (the letters may be different) in a maintenance package.
FIG.2 (click to view)
This microcircuit is the reason for the device failure.
The microcircuit lowers the battery voltage to 4.5 - 5v and stabilizes it. From its output, this voltage is supplied to the main board to power the modulator circuits. For various reasons, the microcircuit may fail. If a break occurs inside it, then power does not flow to the main board. But this is half the trouble. You just need to replace the chip and everything is fine.
It is much worse when a breakdown occurs - then this is an almost 50% guarantee of complete repairability of the entire device. So, the main board will receive voltage from the battery directly. And this will most likely kill the device completely!
In Figure 2, this microcircuit is marked with an arrow. There is noticeable swelling on its body, which indicates 100% failure of the microcircuit.
If necessary, the microcircuit can be replaced with any one that has suitable parameters. The main thing is that it has a stabilized output voltage of about 4.5 - 5v! I even had to install 7805 in a regular case instead of 7805 in the TO case! You just need to sharpen the metal part a little.
If, after replacing the microcircuit, the device still refuses to show signs of life, then there is still a chance to revive it. On the main board, not far from the soldering point of the conductor through which the +5v supply voltage is supplied, there is an SMD transistor (not in all models). Through it, voltage is supplied to the board. Most likely he is in a “cliff”. It is necessary to short-circuit the terminals of its collector and emitter.
If the device works normally after this, then you can either replace the transistor, or simply leave the jumper. Everything will work fine even with a jumper, it has been tested on more than a dozen devices!
If there is no such transistor on the board or the device does not turn on after installing the jumper, leave this idea, more serious components are most likely damaged!
There were cases when the device turned on after the indicated replacements, but the number 9 was displayed on the screen, which slowly began to go out. In this situation, further attempts to restore the device’s functionality were unsuccessful. Unfortunately, the reason for this behavior could not be determined exactly.
