HP 48S IR Loop-Back Test fail

[calculon]

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.

[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

[calculon]

Thanks for the information. I've tried it again against a mirror with the same result. It neither sends to nor receives from another 48S/SX. But what puzzles me is that it does communicate with the printer.

[Jonathan Busby]

(03-12-2021 08:44 PM)calculon Wrote:  Thanks for the information. I've tried it again against a mirror with the same result. It neither sends to nor receives from another 48S/SX. But what puzzles me is that it does communicate with the printer.

Sounds like a hardware failure to me unfortunately :/

Regards,

Jonathan

[John Keith]

(03-12-2021 08:46 PM)Jonathan Busby Wrote:  Sounds like a hardware failure to me unfortunately :/

If so it would be on the receiving side only. The transmitting components clearly work as the OP is able to print.

[toml_12953]

(03-12-2021 07:45 PM)Jonathan Busby Wrote:  

(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

You can sometimes see the LED if you shoot a video with your smartphone pointed right at the end of the transmitter.

[calculon]

Thanks for the helpful tips. All is not lost, as it sends and receives by wire when connected to a PC.

[Jonathan Busby]

(03-12-2021 10:24 PM)John Keith Wrote:  

(03-12-2021 08:46 PM)Jonathan Busby Wrote:  Sounds like a hardware failure to me unfortunately :/

If so it would be on the receiving side only. The transmitting components clearly work as the OP is able to print.

Indeed you are correct Thanks for pointing that out

Regards,

Jonathan

[Jonathan Busby]

(03-12-2021 11:10 PM)calculon Wrote:  Thanks for the helpful tips. All is not lost, as it sends and receives by wire when connected to a PC.

If the problem is indeed in the IR receive circuit on the main PCB, then you can "easily" repair the circuit, assuming that you can open up your 48 with no cosmetic damage using the excellent guide by Han Duong here . The schematic for the circuit can be found in the "HP 48 I/O Technical Interfacing Guide" here ( on page 8 ). To test whether the Clarke 1LT8 SoC's IR receiver is working, you'll first need to determine if the IR receive circuit on the main PCB is damaged, and, if so, fix it. Having done that, if you still can't receive from another HP48S/SX via IR, then I'd check the trace(s) on the main PCB to see if there's a connection to the IR receive pin. If that checks out and you still can't receive via IR from another S/SX, then it's probably a hardware fault in the SoC. All is still not lost though : If you're good with soldering then I'd recommend using a Hakko, an SMD attachment for a soldering iron and some solder paste to de-solder the Clarke SoC and then replace it with a known functioning one from an "as is" or "for parts" HP48S/SX which has, say, a broken display or keyboard etc. but a functioning Clarke 1LT8 SoC. It might be a PITA, but you could definitely fix it

Regards,

Jonathan