HP 48S IR Loop-Back Test fail

[Jonathan Busby]

(03-12-2021 04:39 PM)calculon Wrote:  I've just acquired a 48S that fails the IR Loop-Back test. The screen reads "IRLB 20000". What does this indicate, apart from failure? The calculator communicates perfectly well with my 82240B printer.

The HP48S/SX IR loop-back self test transmits a string at 1200 baud and then 2400 baud and checks, in each case, whether the string is correctly received on a character-by-character basis. Ideally you want to place your calc right in front of a mirror or, failing that, an opaque white surface, but, having the IR/port cover on should also work.

The failure code 20000 indicates that the calc received no characters during the transmission of the IR loop-back self test. Since you have an HP48S, I'd double check this result by placing the calc right in front of a mirror or an opaque white surface as I already mentioned. If you still receive this error, then there's something wrong either with the IR send and receive circuits on the main PCB or in the Clarke 1LT8 SoC itself.

Regards,

Jonathan