Thanks for your help.
Note: I also tested UART4 using another micro-cape board that was working earlier - it also failed.
This was working under Angstrom and Ubuntu.
ubuntu@ubuntu-armhf:~$ dmesg | grep -iE “uart|tty|error:”
[ 0.000000] Kernel command line: console=ttyO0,115200n8 fixrtc root=/dev/mmcblk0p2 ro rootfstype=ext4 rootwait
[ 0.507160] omap_uart 44e09000.serial: did not get pins for uart0 error: -19
[ 0.507505] 44e09000.serial: ttyO0 at MMIO 0x44e09000 (irq = 88) is a OMAP UART0
[ 1.218231] console [ttyO0] enabled
[ 1.222660] omap_uart 481a8000.serial: did not get pins for uart4 error: -19
[ 1.230408] 481a8000.serial: ttyO4 at MMIO 0x481a8000 (irq = 61) is a OMAP UART4
ubuntu@ubuntu-armhf:~$ dmesg | grep capemgr
[ 1.314500] bone-capemgr bone_capemgr.9: Baseboard: ‘A335BNLT,0A5C,2513BBBK0965’
[ 1.322289] bone-capemgr bone_capemgr.9: compatible-baseboard=ti,beaglebone-black
[ 1.354316] bone-capemgr bone_capemgr.9: slot #0: ‘BeagleBone RS232 CAPE,00A1,Beagleboardtoys,BB-BONE-SERL-03’
[ 1.392362] bone-capemgr bone_capemgr.9: slot #1: No cape found
[ 1.429467] bone-capemgr bone_capemgr.9: slot #2: No cape found
[ 1.466577] bone-capemgr bone_capemgr.9: slot #3: No cape found
[ 1.472829] bone-capemgr bone_capemgr.9: slot #4: specific override
[ 1.479431] bone-capemgr bone_capemgr.9: bone: Using override eeprom data at slot 4
[ 1.487466] bone-capemgr bone_capemgr.9: slot #4: ‘Bone-LT-eMMC-2G,00A0,Texas Instrument,BB-BONE-EMMC-2G’
[ 1.497595] bone-capemgr bone_capemgr.9: slot #5: specific override
[ 1.504197] bone-capemgr bone_capemgr.9: bone: Using override eeprom data at slot 5
[ 1.512234] bone-capemgr bone_capemgr.9: slot #5: ‘Bone-Black-HDMI,00A0,Texas Instrument,BB-BONELT-HDMI’
[ 1.522697] bone-capemgr bone_capemgr.9: loader: before slot-0 BB-BONE-SERL-03:00A1 (prio 0)
[ 1.531582] bone-capemgr bone_capemgr.9: loader: check slot-0 BB-BONE-SERL-03:00A1 (prio 0)
[ 1.540465] bone-capemgr bone_capemgr.9: loader: before slot-4 BB-BONE-EMMC-2G:00A0 (prio 1)
[ 1.549338] bone-capemgr bone_capemgr.9: loader: check slot-4 BB-BONE-EMMC-2G:00A0 (prio 1)
[ 1.558137] bone-capemgr bone_capemgr.9: initialized OK.
[ 1.563745] bone-capemgr bone_capemgr.9: loader: before slot-5 BB-BONELT-HDMI:00A0 (prio 1)
[ 1.572511] bone-capemgr bone_capemgr.9: loader: check slot-5 BB-BONELT-HDMI:00A0 (prio 1)
[ 1.594787] bone-capemgr bone_capemgr.9: loader: after slot-0 BB-BONE-SERL-03:00A1 (prio 0)
[ 1.603587] bone-capemgr bone_capemgr.9: loader: check slot-4 BB-BONE-EMMC-2G:00A0 (prio 1)
[ 1.618764] bone-capemgr bone_capemgr.9: loader: check slot-5 BB-BONELT-HDMI:00A0 (prio 1)
[ 1.633551] bone-capemgr bone_capemgr.9: slot #0: Requesting part number/version based 'BB-BONE-SERL-03-00A1.dtbo
[ 1.650222] bone-capemgr bone_capemgr.9: slot #0: Requesting firmware ‘BB-BONE-SERL-03-00A1.dtbo’ for board-name ‘BeagleBone RS232 CAPE’, version ‘00A1’
[ 61.751962] bone-capemgr bone_capemgr.9: failed to load firmware ‘BB-BONE-SERL-03-00A1.dtbo’
[ 61.760833] bone-capemgr bone_capemgr.9: loader: failed to load slot-0 BB-BONE-SERL-03:00A1 (prio 0)
[ 61.772418] bone-capemgr bone_capemgr.9: loader: check slot-5 BB-BONELT-HDMI:00A0 (prio 1)
[ 61.772447] bone-capemgr bone_capemgr.9: loader: after slot-5 BB-BONELT-HDMI:00A0 (prio 1)
[ 61.772475] bone-capemgr bone_capemgr.9: slot #5: Requesting firmware ‘cape-boneblack-hdmi-00A0.dtbo’ for board-name ‘Bone-Black-HDMI’, version ‘00A0’
[ 61.772500] bone-capemgr bone_capemgr.9: slot #5: dtbo ‘cape-boneblack-hdmi-00A0.dtbo’ loaded; converting to live tree
[ 61.772829] bone-capemgr bone_capemgr.9: slot #5: #4 overlays
[ 61.773958] bone-capemgr bone_capemgr.9: loader: check slot-4 BB-BONE-EMMC-2G:00A0 (prio 1)
[ 61.773982] bone-capemgr bone_capemgr.9: loader: after slot-4 BB-BONE-EMMC-2G:00A0 (prio 1)
[ 61.774012] bone-capemgr bone_capemgr.9: slot #4: Requesting firmware ‘cape-bone-2g-emmc1.dtbo’ for board-name ‘Bone-LT-eMMC-2G’, version ‘00A0’
[ 61.774028] bone-capemgr bone_capemgr.9: slot #4: dtbo ‘cape-bone-2g-emmc1.dtbo’ loaded; converting to live tree
[ 61.774534] bone-capemgr bone_capemgr.9: slot #4: #2 overlays
[ 61.774704] bone-capemgr bone_capemgr.9: slot #4: Applied #2 overlays.
[ 61.774719] bone-capemgr bone_capemgr.9: loader: done slot-4 BB-BONE-EMMC-2G:00A0 (prio 1)
[ 61.964834] bone-capemgr bone_capemgr.9: slot #5: Applied #4 overlays.
[ 61.964861] bone-capemgr bone_capemgr.9: loader: done slot-5 BB-BONELT-HDMI:00A0 (prio 1)