"Just go look it up!" wrote:
...
What about buying a same-model, same part# replacement box, new, and
shoving it in to replace defective box? Like replacing a KX-155A
nav/com with another 155a because the 1st one died? All that's
involved is sliding into the tray and securing in place. Airframe
log
notation with new serial number sufficient to be covered as owner
maint?

Sounds good to me. I can't deduce why it need even be a new or
yellow-tagged box; something off eBay on PayPal and a prayer seems to
fit the FARs. :-) If you look at Part 43 in the Appendix re owner
maintenance, you may replace a slide-in box with impliedly anything
that'll work, but you are to perform an operational check as necessary
and should log that test.

Fred F.