Category: reverse

We are planning a new project from this time.
Disassemble a commercial product and learn the technology hidden in it.
This time, I will disassemble the AM / FM radio tuner, KTF5002 made by KENWOOD.
This was sold at HARDOFF in the neighborhood for 1500 yen.

It was a junk item, but it was in good condition, and both FM and AM radios sounded fine.

First of all, I investigated this radio.

When I looked it up, it was released around 1997. It’s one below from my age.
The price is reasonable at 25,000 yen.

The pdf of the instruction manual was also included, so I will paste the link below.

KTF-5002data sheets

This is a Specfication bellow.

　

Reception frequency range of FM radio is 76MHz to 90MHz. It is enough range for FM radio at that time.

Over 90MHz was the band of analog TV audio signals. Currently, this vacant band is the complementary broadcast of AM radio (WideFM).Total harmonic distortion is 0.5%, which is reasonable for audio equipment.

What surprised me personally was that the SN ratio of the FM radio was 70 dB. I think the performance is quite high for that time.

In addition, the SN ratio of AM is 40 dB. After all, AM radio has more noise than FM.

　

Front panel

Let’s remove the cover and take a look at the contents.

I see. I thought it was complicated, but the contents were contained in one board.
Take out the board further.
Roughly, the name of the circuit is shown.
It consists of many circuits such as FM front end, FM multiplexer, AM stereo demodulation circuit, PLL circuit, power supply circuit, etc. I will explain these circuits one by one in future blogs.

Today, I just disassembled it, so I will focus on the entire board.

First, the material of the substrate is a paper phenol substrate. It’s cheap and not very durable, but it’s good enough for stationary audio equipment. The board has a one-sided single-layer structure, and the parts are attached to only one side. Therefore, jumper lines are often used because of the intersection of lines. In addition, the surface mount components are only the microcomputer (thick, …) attached to the back surface, and all the rest are discrete components. All of this part is manually inserted, where the legs of the part are bent behind the board. And you can see that it is cut by human hands.

Also, since there is no unevenness in the soldering, it can be seen that the board is applied to the solder bath and the soldering is done by the flow method. Only the microcomputer may be retrofitted and reflowed with cream solder.

Honestly, I think that this is a considerable labor cost from the current era.

I think it’s amazing that this is sold for 25,000 yen.

Also, the power supply circuit is also noteworthy.

Audio-related equipment is so heavy because it does not use a switching method in the power supply circuit. Switching power supplies are, for example, mobile phone chargers and personal computer charging adapters. If you use switching, the circuit of this radio will be lighter, but switching will generate a lot of noise, so if you use it as a power supply for the radio, the SN ratio will drop at once. Therefore, there is no choice but to place a large transformer and make it with an old-fashioned power supply circuit.

In addition, the display is a display method called VFD. Often, at the supermarket cashier, the pale letters “Gokei 2350 En” appear. Nowadays, there are many liquid crystal displays (calculators, etc.) and LEDs, but this is an old-fashioned display that applies vacuum tube technology.

I hope I can write this in detail in future blogs.

Finally, the back side of the switches. It was pretty simple.

Today was a roughly disassembled report. In the future, I would like to analyze this product in more detail with the following plan. Next time, I will explain the reception principle of AM radio and FM radio on 9/2. I will also touch on the story of PLL and MPX.

Current serialization; “Disassembly survey of FM / AM stereo tuner KTF-5002”

Update	Content
8/26	I disassembled KTF5002 (specifications, disassembly procedure, board configuration, mechanism)
9/2	AM / FM radio reception principle (AM / FM is the main reception method used, what is PLL / MPX)
9/9	I investigated the IC used in KTF5002
9/16	About FM front-end circuit, FM-IF circuit, AM-RF circuit
9/23	PLL circuit principle
9/30	About FM-AM DET circuit
10/7	About FM-MPX circuit
10/14	About Audio AMP circuit
10/21	About power supply circuit
10/28	About VFD display circuit

The day before yesterday, I went to Hard Off in my neighborhood and bought an unfamiliar box and a wii remote controller on impulse for disassembly.

　

This time, I will confirm the identity of this mysterious wooden box.

Even if I don’t know what’s inside, I thought this case could be used in many ways.

First of all, there are 6 spaces on the top where you can put something.

And there were three buttons next to it.

　

The place to put something was two magnets and three terminals in the middle.

Two hypotheses are possible, one is that these two magnets are + and-of the power supply, respectively, and the middle three may be signal lines (three are SPI communication). I have.

Another hypothesis is that no voltage is applied to the magnet, two of the three terminals are + and-of the power supply, and the other one is the signal line. If there is not a lot of data (7 segments, etc.), I think that there is no problem with control like a servo motor.

The back side only has a DC jack.

The voltage is not written and I am scared so I have not applied the voltage yet. The DC jack is a 2.1φ one sold in Akizuki, so it feels very close to you.

Let’s open the inside now.

! !! !! !! !! !! !! !! !!

It was very simple inside. First, there is a microcomputer, a crystal, and a coin battery in the middle.

Let’s take a closer look at the board.

First, from the board, this is a clock.

The microcomputer chip that controls the display system uses ATmega8A, and a 16MHz general crystal oscillator is used for the clock. Also, I think the chip next to it is the RTC (real-time clock).

This is an element that keeps ticking the time accurately and keeps sending the data of the current time to the microcomputer. Even if the power is removed, coin batteries are loaded so that the time can be kept ticking with the least power consumption. The voltage of the coin battery is 3V, while the voltage supplied from the power supply is 5V, so the voltage of the power supply does not flow into the coin battery and the voltage of the coin battery does not flow into the microcomputer etc. There are two.

There were also unmounted parts. First, the 6-pin terminal next to the microcomputer is the program writing terminal. You can easily rewrite the program by connecting it to the ISP terminal of Arduino.

Also, I am concerned about unmounted parts. Especially, the unmounted terminal written as JDY-16 is worrisome. This is a Bluetooth communication module. Perhaps it is for connecting to a smartphone etc. and making the watch such a thing or something like this. I wonder if there are some options. I do not know.

I checked it because it was written on the board as GIXIE CLOCK.

It seems that I got something more amazing than I expected.

After all it was a clock.

Paste the link below.

AZUREST✖️Gixie Clock

These cases seem to be very useful, so I’ll think about something.

It was very interesting.