RB433AH boot fail with serial plugged in !

[Puffer]

Hi all

Just set up a 433AH and I am using the serial port to log some inbound data from a GSM device.
Have several already working similarly.

The unit is up a 6m pole so I made off a mylar screened cable to pins 2,3 & 5 and plugged it in. I left the other end unconnected for now to be able to cut shorter if needed and make off at site. Serial console is disabled and V5.17 installed.
The unit refuses to boot. LED’s light up but no “pings”. If I remove the db9 plug it boots happily !! I have tested it both ways several times. If I plug in a short null modem cable it boots OK. It just does not like a 7m open ended cable !

Any explanations !

[jandafields]

@Puffer

Hi all

Just set up a 433AH and I am using the serial port to log some inbound data from a GSM device.
Have several already working similarly.

The unit is up a 6m pole so I made off a mylar screened cable to pins 2,3 & 5 and plugged it in. I left the other end unconnected for now to be able to cut shorter if needed and make off at site. Serial console is disabled and V5.17 installed.
The unit refuses to boot. LED’s light up but no “pings”. If I remove the db9 plug it boots happily !! I have tested it both ways several times. If I plug in a short null modem cable it boots OK. It just does not like a 7m open ended cable !

Any explanations !

If the cable is not connected to anything, then there must be some noise getting on it and simulating a keystroke or something.

[janisk]

set router to enter bootloader configuration only on “del” key. As this is going to be useful later in installation. (that can be dune through /system routerboard settings menu.