possible HP-9820A error code?

[donsp]

I've recently acquired two HP-9820As. One seems to be working, but the other displays "0E NB" when turned on (and the "E" looks bold). Pressing any key will momentarily blank the display, and this string is redisplayed. It occurs with or without a ROM installed. (There is no paper in the paper feed.) Admittedly, I haven't read much of the available documentation, but this form of error message does not pop out. Is this most likely a random string, and the problem is more serious than I hope? Any pointers would be appreciated. (I just downloaded the PDF of 98xx repair.)

I'm new here, and hope to participate more constructively :-) I collect all types of calculating devices, from pinwheel calculating machines to Primes. I'm currently building up a nice stable of 9800 family machines.