Routerboard startup beep key

can someone point me to a list that defines the startup beeps. Normally I see one beep, 50 sec delay, then 2 beeps and the system is ready.

However I just finished work on a RB102 that beeped 3 or 4 times before the system was available. What does this mean??

RB112 starting up provides the following beeps:
one beep when board is switched on,
two beps when RouterOS is booted up.
You can connect null modem cable to check it out, what happens during bootup process.

sergejs, yes but what does 3 or 4 beeps on startup mean - is it always indicating an error? meaning I should connect a serial port, or can I look at the device’s log?