Sub: - Steps to avoid electronic card failure.

          There have been a few line failure cases of EMD locomotives due to card failure.

          It is requested to kindly incorporate following measures in shed maintenance Practices to avoid electronic card failure.

Cause of failure	Preventive measures
1. Card handling Most printed circuit boards (PCB) are Electro statically Sensitive Device". They are designed for operation voltages of max. 15 Volts. Isolating materials such as plastic films or clothes made of synthetic material may be charged to 10 000 Volts or even higher damaging a low voltage PCB. The damage may happen in a way that the PCB continues operation for several weeks, until it finally fails.	Before touching a PCB, the person carrying out the work must be electro statically discharged. The simplest way of doing this is to touch an electrically conducted earthed object. PCBs must not be allowed to come in contact with electrically insulating materials such as plastic foil, insulating table tops or clothing made of synthetic fibers. Grounding of n computer equipment /PCB should be ensured before working on it.
2. Card storage - Un protected or kept in open condition Electronic components and assemblies that are sensitive to electrostatic discharge damage may are likely to fail.	PCBs should be kept or stored on electrically conducting surfaces only. While carrying out soldering jobs on PCBs, make sure that the soldering tip has been earthed .PCBs and electronic components should generally be packed in electrically conducting bags. Bag containing PCB should not be opened without properly grounding it. Protective measures necessary when dealing with sensitive electronic components during repairing and testing are- Conductive flooring.  b)  Anti-static table  c)   Anti-static footwear.  d)  Anti-static overall. e)   Anti-static chair.         f)  Cabinet earth connection

Cause of failure	Preventive measures
3. Loose fasteners - Loose fasteners in card holding slots to chassis or front male/female plugs may cause severe damage initiating voltage fluctuation, surge development and sparking at contact points of the card resulting temporary or permanent malfunction.	Ensure fasteners are properly tightened. Use only recommended tools during installation and removal .Cross threading often damages body threads. If thread damage is noticed, rebuild the thread with proper rebuilding material. Check individual component vibration by Vibration meter to detect the degradation of fasteners.
4. Damage due to arc welding - Electronic components and assemblies are often damaged due to unprotected welding practice.  Surge development on car body during welding may cause sensitive modules to fail due to low insulation resistance of control circuitry.	Follow welding precaution as recommended by the manufacturer or as per locomotive service manual strictly .Isolate battery knife switch along with all Circuit breakers. Remove all cards from chassis and connecting plugs before welding.
5. De-soldered or loose electronic hardware – Electronic cards sometimes may misbehave or malfunction due to loose soldering or soldering failure.	Using Thermal imaging device, the flaw can be detected earlier before it fails .The different color bands indicate different thermal zones. Abnormal thermal development due to deteriorating component or failed soldering can be detected by thermal imaging device. Even magnifying glass will be able to help in case of thermal discoloration.
6. Improper grounding of Cards- Due to improper grounding electronic cards may also fail.	It should be ensured that the card chassis or body is well grounded. Ground continuity and ground resistance test should be conducted.
7. Cooling and ventilation - Improper cooling and bad ventilation may create severe damage to the electronic cards.	The cooling facility should be checked for their efficiency. Air filter condition is also responsible for improper cooling. Manometric test of the system should be carried out in medium schedule to check cooling efficiency.

Cause of failure	Preventive measures
8. Dust and moisture – Dust and moisture are major contributor towards card failure.	Working environment should be dust and moisture proof .The unwanted particles accumulated over electronic components create short circuit as soon as they come into contact with moisture. Panels should be always dry and free from moisture. It should be encapsulated with proper gaskets and sealant. If pollution (dust, moisture, etc.) is detectable, check: Sealing gasket adjustment of bayonet locks Compartment walls for leakages. Air filters condition. To clean the card compartment, use a vacuum cleaner and a lint free cloth.
9.Trouble shooting technique-	Analogue signature analysis- In this technique a current limited AC sine wave across two points of electronic component or circuit is applied. The current / voltage waveform is shown on a signature display using vertical deflection for current and horizontal deflection for voltage .This unique analog signature represents the overall health of the part being analyzed. By comparing the signatures of known good circuit boards to those of suspect boards, faulty PCBs and components can be quickly identified.  Shed should make data base of analog signature of each PCB  for referral purpose. Power – off testing This testing is often necessary to test the printed circuit assembly board due to uncertainty of fault nature. When the PCB can be further damaged by applying power it is necessary to use power off test techniques to safely examine it .This technique includes Analog signature analysis, Ohmmeter, LCR meter and optical inspection .This type of testing also lends itself well to troubleshooting circuit boards without the aid of supporting documentation such as schematics.