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IBM 5150 motherboard  -  Trimmer T1 replacement




Trimmer capacitor T1 is of ceramic type, and its adjustable value is 5-30 pF  (5 pF at the minimum setting, ranging through to 30 pF at the maximum setting).

Note that the capacitor is a necessary component in the circuitry that generates various clock signals.  See the adjustable capacitor at the far left of the diagram at here.  Without the capacitor, there will be no clocks.

You should be able to find a replacement online.  It does not need to be exactly 5-30 pF.  For example, 5-50 pF covers the 5-30 pF range.

If you are seeking a replacement that will 'pop straight into' the three holes left behind from removing the old capacitor, then pay attention to the inter-pin spacing.  Otherwise you may need to bend a leg on the replacement, or do another trick to fit the replacement.


Option of fixed value

The fact that the capacitor is adjustable (rather than fixed) is for possible adjustment when a composite monitor (or TV) is the display, attached to the composite video out of the CGA card (the card's RCA jack) - adjusting the trimmer fine tunes the colours that appear.

Adjusting the trimmer has no effect on the colours that appear on a digital monitor (i.e those connect to the DE-9 connector on MDA, CGA, or EGA cards).

If you do not plan to use composite video, consider using a fixed-value capacitor as the trimmer replacement.  Diagram at here.  20 pF is my suggested value.

Even if you are planning on using composite video, a fixed-value capacitor as the trimmer replacement may be good enough for you (the on-screen colours are good enough).