The KA921 is now running (at least on AC, I haven't checked the DC supply yet). The failure was bad caps on the B+ line, and an open resistor and inductor. I also found this split open:
I assume this is a varistor, but I do not know the value. Assuming the 250 is 250V none of the suppliers I know of carry 250V varistors. Am I reading the value wrong? This one reads open circuit, but I do not not remember if these are meant to go open or short when the voltage across them goes high.
It has good color and plenty of brightness, but the convergence is a bit out. It does need some serious degaussing, so hopefully the convergence will improve once I degauss it. I've finally ordered a degaussing wand as I've been doing without one for too long (not specifically for this set, I've found 4 recent sets on the side of the road this week that appear to need nothing more than degaussing).
I still don't have a definite date for either of these. So far my best guess would be that the KA910 is from around 82. Now that I've have a closer look at the chassis it appears the KA921 is actually later than I expected, probably around 86 or even later. The design is similar to Sharp sets that were in a more modern style cabinet. I guess Philips updated the chassis, but recycled the old cabinet design.
The design of both sets is unusual compared to most of the AC/DC sets that I have seen. There are completely separate AC an DC power supplies. Most others that I have seen so far have either a basically conventional AC set chassis that is driven by a step up DC-DC converter when running on DC or 12V is the B+ and it runs from an internal 12V power supply when on AC.
As for other small Philips sets I've seen a mid-late 80s 6" AC/DC set here, but I don't have one of those yet.