I am trying to replace a Hex D Flip-Flop on an Amiga A4000 motherboard. The original chip has the label


Motorola HCT174A

I believe the datasheet describing this is the MC74HCT174A (though I can't find a reference to the XAA346), however, a BOM for the Amiga Motherboard lists

74HCT174, SOIC package
74HCT174, SM, EIAJ Package (as an subsititue)

When when I search Mouser.com I find 5 possible choices and the TI CD74HCT174M (datasheet) seems like the correct choice, is there anything to keep in mind when sourcing a replacement?

  • \$\begingroup\$ What did that? battery acid? all the copper is gone, it looks very hard to repair. \$\endgroup\$ – Jasen Nov 25 '18 at 5:02
  • \$\begingroup\$ yeah battery acid, I actually have a reprinted A4000 D Rev. B motherboard that I am transferring the non-damaged original chips over to. Amazingly when I received this motherboard it actually booted with this damage, though some diagnostic software suggested it was slower than Amiga 5000 so I'm sure some bizarre things were going on inside. \$\endgroup\$ – Jason Sperske Nov 25 '18 at 5:09

74HCTxxx is a standard logic family (just as 74HCxxx, 74LSxxx, 74ALSxxx, etc.)

All manufacturers were supposed to abide to the same nomenclature, input and output logic levels, fan-in, fan-out, and timing.

Parts within the same family are supposed to be manufacturer-independent.

Furthermore, 74HCT parts were designed to interoperate with both 74HC and 74LS parts, to give more freedom to the designer.


What you are looking at is indeed a 74HCT174. This is a standard logic IC, so TI's version of the part (which you've found) should be perfectly acceptable. Hardware makers of the time would frequently substitute equivalent parts from different manufacturers -- notice the Philips 74HCT166 right above it, for instance.

The "XAA346" on the second line is a manufacturing code or lot number -- properly decoded, it can probably be used to determine when and where that specific IC was manufactured. You can safely ignore it.

  • \$\begingroup\$ Both answers were very helpful, so I ended up selecting based on time answered (though even that was close), but I wanted to still express my thanks :) \$\endgroup\$ – Jason Sperske Nov 25 '18 at 6:17

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