IBM 51xx motherboards/cards - Types that are wired to use 3-legged tantalum capacitors


You are here because

You are here because you have a variation of IBM 51xx (5150/5155/5160) motherboard or card that is wired to use 3-legged tantalum capacitors, and one or more of those capacitors is faulty.

( Note: Different to the type that is wired to use 2-legged tantalum capacitors. See here. )


Background

As shown in the image below, in the world of electronics, it is possible for 3-legged tantalums to have two types of polarity.




Which did IBM use in the IBM 51xx ?

For the IBM 51xx (5150/5155/5160) motherboards/cards that are wired to use 3-legged tantalum capacitors, the wiring is such that a capacitor of negative-positive-negative polarity is required.

Always, irrespective of whether the tantalum capacitor is filtering a negative or positive voltage rail.  See here.


Option 1 of 2: Replacing 3-legged with 3-legged

On the IBM 51xx motherboards and cards that are wired for 3-legged tantalums, when you replace a faulty 3-legged tantalum with a 3-legged replacement, the replacement must be of the same polarity.

The 3-legged tantalums are of the negative-positive-negative polarity, and of 10µF/16V. They typically have "106 16V" or "10µF 16V" marked on them.

Once you have a suitable 3-legged replacement (of capacitance/voltage/polarity), it can be soldered on to the PCB in either orientation (lettering to the front, or lettering to the back). That is because the same polarity relationship is maintained - positive leg into positive hole, and negative leg into negative hole.

The diagram below is for a particular negative-positive-negative 10µF/16V 3-legged tantalum made by Kemet, and available at Mouser Electronics:
Mouser part number: 80-T398E106M16AT
Kemet part number: T398E106M016AT





Option 2 of 2: Replacing 3-legged with 2-legged

On the IBM 51xx motherboards and cards that are wired for 3-legged tantalums, there is no reason why you cannot replace a 3-legged tantalum with a 2-legged one.
Ensure that you observe correct polarity - positive leg into positive hole and negative leg into negative hole.