Home
EMC Troubleshooting in PC Design
Contents
1. C test items which disguised the root cause The CE result of power port and RE result of EUT are all passed The only failure is shown in CE of telecom port Thus the early detection is focused on the telecom port of the motherboard Some solutions on the motherboard were tried but in vain Then the attention was transferred to the set ups and peripherals of the CE test yet the alternative tests proved that they had no relation with the failure The breakthrough occurred when another model of adapter was used in the test and the result turned passed The near field antenna is employed to detect out the victim spectrum on the output terminal of the suspected adapter instead of on the motherboard Thus the real source is found The suspected adapter once resulted in curve problem at displaying port of the host system has a grounding resistance of 10 Q as R in Figure 3 at the protect earthing PE line of AC input terminal If this 10 Q resistance is removed the CE test of telecom port will turn passed However the curve problem at displaying port will re occur So this 10 Q resistance can t be removed The final solution of Cy in Figure 3 is a combination of capacitances of 1 000 pF and 470 pF It will not impact any other performance of the system And we see that EMC solution should be the compromised result when considering other functions of the system Case 2 Radiated Emission Suffered from CPU Heat Sink Grounding The process
2. MA TROUBLESHOOTING EMC Troubleshooting in PC Design Lv feiyan Cao Xin Wang Liang Lenovo Beijing Co Ltd Abstract Two EMC cases in personal computer PC are presented as one on conducted emission coupled from power port to telecommunication port the second one on radiated emission derived from poor ground in motherboard The retrospect of debug and analysis process is illuminated for system EMC design Keywords EMC debug PC telecommunication port grounding Introduction ersonal Computer PC is mostly used in office and home environment sometimes used as controlling center in industry sites Hence the EMC design for PC should consider carefully the susceptible instruments surrounding to reduce the EMI as less as possible to meet Class B level per CISPR 22 PC is built up with CPU memory displaying unit and peripherals The peripheral sub assembly parts and motherboard have compatibility issues in the design stage Troubleshooting is made in light of the whole system as EMC design and analysis should not impact the host performance This paper shares two cases in EMC design and debug in PC fallen into scope of conducted emission CE and radiated emission RE respectively Most of the contents are given to describe the intricate process of detecting root cause and of solution trying to illuminate the readers Case Conducted Emission from the Power Port Coupling to the Telecommunication Port This c
3. ase is of the influence of common mode CE from the power port especially in the adapter to the telecommunication port of the host system In the CE test on telecommunication port the result shows failure in the frequency band 3 8 4 5 MHz as Figure 1 The high emission in this band is not influenced by the data rate and format of telecommunication port The frequency spectrum can be detected with loop antenna at the DC output terminal of the power adapter Also the same spectrum can be detected on the outer shield of the enclosure of EUT It is proved that the outer surface current on the 30 SAFETY amp EMC 2013 outer shield is coupled from the adapter since the ground GND of the adapter output DC terminal is grounded on the enclosure The CE test result is ameliorated as shown in Figure 2 The final solution is some capacitances by passed at the DC output circuit of the adapter as in Figure 3 120 CISPR2 2 CLASS B V OP gt D 0 0 2 0 5 1 0 2 0 5 0 10 0 20 030 0 f MHz Figure 1 CE test result of telecommunication port of EUT 100 0 2 0 5 10 20 5 0 10 0 20 030 0 f MHz Figure 2 CE test result of telecommunication port of EUT with re worked adapter Circuits inside adapter 5 a filterin 2 tran nsforming and DC filtering Figure 3 Circuit scheme of the re worked power adapter of the EUT The debug process is tortuous due mostly to the perfect results of other EM
4. ced estimation on where and with what means to ground Many EMC analysis models are abstracted from complicated system with many elements omitted Such models are popular Figure 7 Improved metal set up of the grounding screw of CPU heat in many textbooks Yet the magic of EMC troubleshooting lies in sink the process of detecting root cause when passing through many Eos specious factors Even the source is found the solution is more than details It s the representative case in EMC that a slight modification P one means The engineer should consider both the cost and the on one part may affect the whole system easy reproduction in mass The final one is preferred that is cost controlled and easily put into mass production in manufacturin Conclusions k i assembly There re three types of EMC solution as grounding filtering and shielding Shielding is to cut off the EMI transferring without References getting rid of the interference source from the root So if the root 1 CISPR 22 Information technology equipment Radio disturbance cause is in the motherboard the same over limit failure will characteristics Limits and methods of measurement S 2008 re occur when the motherboard is employed in another computer 2 Lv Feiyan Caoxin Zhou Hui Influencing Factors in Conducted system to require the second re work Besides shielding material Disturbance Test for Telecommunication Port According to GB 9254 will resul
5. layer is emitted by means of the CPU heat sink When the grounding of the screws is insulated with the fourth layer the EMI test passed see Figure 5 55 731 256200 MHz 855 900233 MHz 50 46 327 dB u V m 46 942 dB p V m E dB u V m 0 4 30 200 400 600 800 1 001 f MHz Figure 4 RE test result before solution 50 EN 55022 Electric Field Strength 3 m QP E dB u V m 30 200 400 600 800 1 001 f MHz Figure 5 RE test result after solution The final solution including two steps one is re configuration of the backboard of the CPU heat sink as shown in Figure 6 Figure 6 Re configuration of the backboard of the CPU heat sink The second is that the metal set up of the screw holes is changed as Figure 7 The two steps guarantee the effect in mass production The screw of CPU heat sink is only one small part of thermal design yet its effect on EMI performance is magnified when stimulated by the little re arrangement of grounding point in ground layer This case reminds the R amp D engineers that system design should concern beyond the circuit scheme to the realizing technique SAFETY amp EMC 2013 31 W TROUBLESHOOTING practically Filtering and grounding is aimed at root cause For filtering the magnetic coils or capacitance is frequency selective so that many tests might be tried before the right one is found Grounding is the best way for both solution and cost yet it needs experien
6. t in cost up So shielding is always the last choice 2008 J Safety amp EMC 2009 4 17 22 he amp J 8 RL A i SBF Honeycomb Vent Wave Guic e HUAMING Electronic Equipment HM HV series honeycomb vents are widely used in EMC shielding field for the air refresh system of the RF shielding room microwave chamber or RF shielding box The available materials include tin steel brass and copper The choice of the honeycomb vent with the best design is based on the RF shielding performance and air flow WWW EMCFittings COM WWW EMC Enclosure COM Address No 2 CHENGXI Industry Park Renmin East Road Wujing District Changzhou Jiangsu China TEL 0086 519 86651804 Mobile phone 13961296476 FAX 0086 519 86695916
7. to figure out the root cause of EMI is always a tough work The engineer should be expert in the motherboard not only in layout such as routing layer division grounding split but also in the craft In this case the layout scheme is perfect in the blue print yet a little change of grounding means of the CPU heat sink resulted in EMI over limit at frequency band 800 900 MHz The peripherals are excluded since it s noticed that the victim EMI is not derived from I O ports of the EUT During the RE test the victim EMI occurs when the displaying port is activated with full screen of characters Thus the data transferring between CPU and memory card is suspected The routing in Gerber file is checked to find that there re four pairs of high speed lines for graphic function with 3 pairs running at top layer of the motherboard while the fourth pair is routing at the bottom layer The fourth pair of lines is not grounded at GND but on reference voltage port U4 Thus the bottom layer is noisy The root cause is explored but there s no time to return the motherboard to re routing Finally the engineer found that the TROUBLESHOOTING W victim spectrum disappeared when replacing another type of CPU heat sink The new CPU heat sink differs in grounding means of screws When the CPU heat sink has electrical connection with the fourth layer by grounding of the screws the RE test failed see Figure 4 So we can see that the dirty EMI on fourth
Download Pdf Manuals
Related Search
Related Contents
Manual de Usuario - Domotica y Seguridad -充電器 FUENTES DE ALIMENTACIÓN DE CC Agilent E361xA DE 60W EN Makita TW0350 User's Manual Unidad de comunicación visual HD KX Newstar FPMA-D200BLACK flat panel desk mount ASUS K200MA J8798 User's Manual Copyright © All rights reserved.
Failed to retrieve file