VoltCraft VC830, VC440 multimeter is assembled on a special microprocessor FS9922-DMM4, developed specially for digital multimeters by the Taiwanese company Fortune Semiconductor. FS9922 is slow by modern standards.
Multimeter VoltCraft VC830, VC440 has only an automatic selection of the measurement limit. Therefore, it is slow in operation, since the FS9922-DMM4 microprocessor itself is slow.
In this case, a VoltCraft VC830 multimeter measured the voltage in resistance mode. As a result, several transistors of the automatic measurement limit selection circuit and part of the center switch track turned out to be failure.
After replacing the transistors and soldering a new foil to the burned parts of the track, the device started working.
In the photo, the repair places are circled in white. The photo of the enlarged part of the restored central switch is also glued in. It can be seen where the soldered new foil.
FS9922-DMM4 is an 8-bit processor with two integrated ADCs. One ADC is accurate (3 measurements / s), for digital readings, the second ADC is fast (30 measurements / s), for a 60-segment linear scale. The microprocessor has a hardware KOM port. It has low power consumption (U = 2.4-3.6V, I = 2mA). Output 3 3/7 characters, digital LCD display with a resolution of 6000 counts. For comparison, the cheap Chinese multimeter of the M830 series has 3.5 digits and displays only up to 1999 counts at a speed of 2.5 measurements / sec.
Microprocessor FS9922-DMM3 has 4000 samples with the same parameters and speed.
The FS9922 is manufactured using the technology of large integrated circuits with a high degree of integration, which means that all the nodes of the circuit are integrated into the processor. Even a buzzer and a managed backlight driver.