How do you repair a switch when a power supply problem arises? This paper describes in particular the methodological steps for power maintenance of switches and some lessons learned。
Reference: https://www. Eepw. Com. Cn/article/201612/327449. Htm
Specific methods for power maintenance on switch-off
In the maintenance of power switches, we first need to check whether power units have been hit by short circuits, such as power consolidation bridges, switch tubes, high-frequency high-power current tubes, high-power resistance to suppress currents, etc., using a universal meter, and then we need to check whether the power barriers at each output voltage end are abnormal, and we need to replace new ones if the above items are damaged。
Once we have completed the above-mentioned tests, and if the power supply is not working properly, then we have to test the power factor module (pfc) and the pulsed components. Pwm, looking for relevant information, familiarizing itself with the functionality of each foot of the pfc and pwm modules and the conditions necessary for normal operation of the modules。
For power sources with pfc circuits, it is necessary to measure whether the filter capacity at two ends is around 380 vdc, if around 380 vdc indicates that the pfc module is working properly, then to monitor the working state of the pwm component, to measure its power input end vc, to refer to vr, to initiate control of vstart/vcontrol end voltage, to use 220 vac 220vac isolator transformers to power the switch power, to observe whether the waveform of the pwm module ct to the ground is a linearly sound saw or triangle, such as the tl 494 ct end is a sawt wave and the fa 5310 ct end is a triangle. Whether the wave shape of the output end v0 is an orderly narrow pulse signal。
In the operation of power maintenance on switches, many of the power switches use 8 foot pwm components of the uc38x series, most of which are not working because of power-starting resistance damage or decreased chip performance. When there is no vc after r breaks, the pwm component is not operational and has to be replaced with the same resistance as the original resistance. When the pwm component is activated, the r value can be reduced until the pwm component is operational. When repairing a gedr power source, the pwm module was uc 3843 and no other anomalies were detected, and the pwm component worked on r (220k), followed by a 220k resistance, and the output voltage was normal. In some cases, the vr end 5v voltage was 0v and the pwm component was not working as a result of external circuits connected to the vr end were cut off, the vr was converted from 0v to 5v, the pwm component was operational and the output voltage was normal。
When the filter cap is free of around 380 vdc, it is indicated that the pfc circuit is not working properly, the key test foot of the pfc module is the power input vc, kick start vstat/control, ct and rt feet and v0 feet. When repairing a fuji 3000 camera, testing a panel of filters without 380 vdc voltage. Vc, vstart/control, ct and rt waveforms and v0 waveforms are normal, and the measurement field power switch g is extremely v0-size-free. As fa 5331 (pfc) is a sticker component, the machine has been welding between the end of v0 and the plate for a long time and the v0 signal did not reach the field effect tube g. Welding of the v0 end with the welding point on the plate and measuring the filtering caps with 380 vdc voltage using a universal meter. When the vstart/control end is low level, the pfc is unable to work, and the relevant circuits connected to the outer edge of its endpoint are tested。
In general, switch-off power circuits are difficult, power is large and small, and output voltage is diverse. By capturing what is at its core, i. E. Fully familiar with the basic structure of the switch and the characteristics of the pfc and pwm modules, the basic conditions under which they work, and by following the above-mentioned steps and methods, more hands-on maintenance of the switch power, the power failure of the switch can be quickly eliminated and the effect of the half-work factor achieved。
Switching power maintenance experience
When the power of the switch does not turn on, we usually need to see whether the switch frequency is correct, whether the protection of the circuit is blocked, if the voltage feedback circuit, if the current feedback circuit is okay, if the switch is punctured, etc。
Switch the power transformer heats up or makes a "polymer" sound, usually with an incorrect switch frequency。
The switch-off output power source signal is generally short-circuited。
