The Kantronics KPC9612 / KPC9612+ is a TNC which also offers the option to send POCSAG messages. This requires a suitable firmware version for the TNC. The Kantronics website you’ll find a good overview of all available firmware versions:

Be aware firmware can’t be downloaded via the Kantronics website!

The notes below refer to the KPC9612 (non-plus)

While updating the firmware from version 7 to version 8.2 some weird behavior showed up. After writing an EPROM the TNC wouldn’t boot with firmware 8.2. After inserting the version 7 EPROM again, the TNC started as expected.

Some research revealed that the new EPROM was a pin compatible 2 MB chip, while the original was only 1 MB. On first sight this wouldn’t cause issues, but on a test the TNC didn’t boot anymore. So the issue had to be related to the larger EPROM.

Searching the internet revealed a manual of a slightly different version of the 9612 (probably there has been a revision of the PCB). This manual was only partially usable, because it mentioned a 27C512 EPROM for the firmware, which is a completely different and NOT compatible type. But the manual also revealed the behavior of jumper J13.

Right below: jumper J13

According to the manual this jumper distinguishes between an EPROM larger or smaller than 1 MB. The jumper in position ‘1’ means there is an EPROM of 1 MB (or smaller) in the socket. Position ‘2’ is needed for an EPROM larger than 1 MB. After changing the jumper setting (remember to disconnect the power first!) a hard reset needs to be done. Afterwards the TNC boots the new firmware flawlessly.