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Today we disassembled a BK Precision frequency meter made in the United States, model 1856D, 3.5GHZ bandwidth, LED display can provide up to 9 digits of resolution. The high precision and high sensitivity of the frequency meter are widely used in laboratories and frequency test and detection equipment.
I am posting a disassembly post to see if there are any knowledgeable friends who can estimate the cost of this device and see what components are used in this foreign device.
Before disassembling, I checked the manual of this device and found that it supports two power supply methods, one is AC150V and the other is AC230V. The comparison of resolution and test accuracy is still quite high.
Next, remove the protective shell and then remove the 4 screws under the shell. At this time, you can remove the back shell. The screws on this frequency meter must be removed with a plum-shaped screwdriver.
Then remove the outer shell and the bracket. At this time, a metal shielding cover appears (the test instrument still has certain requirements for the interference source), and the entire circuit board is partially wrapped inside. At this time, remove 1 shielding cover cover screw, remove the shielding cover, and expose the circuit board;
Next, take a closer look at the composition of the front PCB board. It can be roughly divided into three parts: display circuit, power supply circuit and main control circuit, etc. There is a metal cover on the lower left side of the board, which we will disassemble and study later. At this time, two crystal oscillators were found, one HC-49UM package frequency is 11.0592MHZ, and the other is wrapped in a metal shell. Through the small hole, it can be seen that it is a 10MHZ frequency source crystal oscillator. It is inferred that the functional crystal may be used as a standard 10MHZ frequency source.
AT89C52 is a low-voltage, high-performance CMOS 8-bit microcontroller. It contains 8k bytes of rewritable Flash read-only program memory and 256 bytes of random access data memory (RAM). The device is produced using ATMEL's high-density, non-volatile storage technology and is compatible with the standard MCS-51 instruction system. It has a built-in general-purpose 8-bit central processor and Flash storage unit. The AT89C52 microcontroller is widely used in the electronics industry.
By consulting the manual, it is found that the supported frequency range is 3MHZ~24MHZ. The actual selected frequency is 11.0592MHZ. Why choose 11.0592MHZ? (Conclusion as shown in the figure) Therefore, 11.0592MHZ crystal oscillator is often used in some serial communication designs to reduce the bit error rate. The models of YXC crystal oscillator used are as follows:
YSX321SL 11.0592MHZ 20PF 10PPM X3225110592MSB4SI
HC-49US 11.0592MHZ 20PF 20PPM X49SD110592MSD2SC
Let's take stock of the main IC information on the circuit board:
1) AT89C52 ATMEL MCU,
2) KID65783AP KEC 8CH HIGH-VOLTAGE SOURCE DRIVER
3) 2 74HC245 Nexperia Octal bus transceivers
4) 2 74HC393 Nexperia Dual 4-bit binary ripple counter
5) GAL16V8D-25LPN Lattice
6) 74HC138 Nexperia 3-to-8 line decoder/demultiplexer
7) 74HC374 Nexperia Octal D-type flip-flop
Several transistors, MOS tubes and electrolytic capacitors. The disassembly is complete. Put them back in order, plug in the power supply, press the switch, and start the machine normally. There are several chips that I can't find information about. Welcome to add or correct them.
