TECH TALK

A journal of bus architecture tips & techniques

Preventing & Fixing Bent Pins

VMEbus, CompactPCI, and other high performance architectures adopted a pin and socket mating convention.  While regarded as reliable and durable, it is not without problems.  Missing pins or bent pins, connector alignment errors, cracked shrouds, or even debris trapped between pins are not uncommon experiences.  Any one of these can cause damage to the board, backplane, or other system components.  A single bent pin in a backplane can shut down a system requiring costly repairs.

What can you do if you have a bent or damaged pin? If you’re lucky, you may be able to straighten it. Most of my bent pins have been caused by careless handling. Fortunately, I was able to straighten them back to a working position. If the damage is too extensive, replacement of the board or backplane is likely.   Figure 1 shows an example of this damage.
	Figure 1.   Damaged Shroud & Bent Pins   (VME64X P0)

About Pin and Socket Designs
In most pin and socket architectures, the board has pins and the backplane sockets.  The reasoning:  it is easier to replace a damaged board than a damaged backplane.  This is true for VMEbus.  Irreparably damaged pins on a VMEbus board are not as catastrophic as damaged ones on the backplane.  You can easily replace a board if you have a spare.  Only VME64x backplanes with the P0 connector have the potential for bending a pin.  A bent P0 pin can be catastrophic.

CompactPCI broke with convention by specifying pins on the backplane and sockets on the board.  CompactPCI also has delicate 2 mm pin pitch (thinner than VMEbus) and higher pin counts (up to 535 per 6U slot).  Connector and pin damage happens more frequently in CompactPCI systems.  Severely bending or breaking pins on the CompactPCI backplane can trash an entire system.  Replacing a backplane causes plenty of inconvenience, lost time, and money.

The architects of VMEbus and CompactPCI specified alignment hardware to properly mate the boards to the backplane.  Shrouds surround each set of pins on the VMEbus board and CompactPCI backplane.  The shroud protects pins when the board is not installed in the chassis and also helps guide the pins into the sockets.  Guide lugs and coding keys prevent mating incompatible connectors between the board and backplane.  Over the years, connector manufacturers have improved pin durability, pin shape, and alignment mechanisms. Despite these safeguards, improper and careless installation can still lead to damaged connectors.  See Figure 2.

Figure 2.   Cracked Shroud (CompactPCI P1 Connector)

Prevention is Best
You can best prevent bent pins by treating your system with lots of love and care.  Here are a few dos and don’ts to help keep your system damage free.

• Carefully inspect your boards and backplane connectors for damage or obstructions before installing the boards into the backplane. 
• Don’t install boards with bent pins or damaged shrouds or sockets.  This may cause further damage.
• Don’t force pins into a socket with irregular or obstructed holes.
• If you suspect an unusual amount of force is required to seat your board, stop to inspect the connectors again.
• Do take special care when removing a board.  Use the ejectors to release the board and pull it straight out.  Jarring or twisting a board free of the backplane can cause damage.

How Can You Repair Bent Pins?
If a system contains one or more bent or crushed pins, first unplug the system.  In the case of minor bending, pins can be straightened without noticeable problems. Try using a pair of needle-nosed pliers, tweezers, or other small tool to carefully straighten the pin.  Pins are usually made of copper and straighten easily.  The pin could break while being straightened, so be careful.

For bent CompactPCI backplane pins, you may want to try a 2 mm HM pin repair kit (Tyco part 354687-1).  I’ve never used this tool but have heard it sometimes works. Your success may depend upon the backplane construction.

In-house repair of severely bent pins is often difficult if not impossible.  Serious damage will probably require replacement of the backplane or board.  For backplane damage, remove the backplane from the enclosure and ship it back to the manufacturer for repair or replacement.  To avoid a wiring headache, you can ship the entire enclosure to the manufacturer who can repair the backplane then test the system thoroughly before shipping it back to you.

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