roccodog: now only showing what looks like a 'P n' on the numeral display
Pn is one of your 9 or so Programmed radio stations. This has probably not been set-up since you bought it.
I have a BM 5000, not a 5500, but with mine you can bypass the MCP by pressing the BM 5000's panel where it says [OPEN] on the bottom left. From there you have access to a number of the controls including being able to select the radio bands and program the stations. (unless if like on one of my BM 5000s you have faulty wiring, in which case only an MCP can help, or you need to get into some simple repair work ... but be careful: this can lead to stage II of the BeoVirus from which most don't recover )
What is state of the batteries in your MCP ?
Do you have all the necessary manuals ?
Also check out the BeoTech site !
And I am sure you will grow to love your purchase ... not such thing as a "duffer", just some old kit that needs TLC
First B&O (1976) was a Beogram 1500 ... latest (2011) change has been to couple the BL11 with the BL6Ks *sounds superb*