I say, scrap an old TV remote and get the missing part from it! 

That would be a good start, yes. I like that idea.

However, I think the problem is deeper than that. Even with the button removed from the MCP, and black tape covering the push pad, it still constantly spams the radio function.

I'm not really great at putting YouTube vids into my posts, but I'll try it again.

The center pad is normally covered by the small springy bronze plate.
What happens if the black tape isn't touching the center pad of the Radio button?

And what's that orange powder-looking stuff? Something spilled? Acidic?

Martin

So far I've tried the MCP with the black tape over the pad, and with out the tape entirely. I've also cleaned the contact pad with electrical cleaner. Still does the same thing and broadcasts the radio function constantly.

I did not notice orange powered? There are no physical sings of battery leakage. It's pretty clean.

So the contact was probably removed in an attempt to make it stop sending.
The problem must be elsewhere, then.
Try putting an ohmmeter across the contact points, compare with readings from other buttons pads.

It looked like orange powder on the backside of the front panel in your photo. Perhaps it's just light reflections.

Martin

When I used my ohm meter, the circuit did not have any connectivity that I could find. (Display stayed OL). After looking at the picture again, I can see how there is some light that makes things look somewhat orange. Probably due to my camera, it's pretty old for a digital, and the picture quality isn't up to par.

The person who sold it to me texted me back last night saying that he'd refund me that part of the purchase. I've found another on flebay, so I'm just going to give up on this one and try the next.

Since I have the proper Beocord 5500 and a Beogram 5005 now, I have been able to listen to the system, and it does sound good. Though there may be a few small issues with the Beomaster 5500, but I'll post about them when the time comes, and with a proper thread title.

Thanks, Andrew

Update Saturday morning:

The new MCP 5500 came in this morning. I was very happy when I put the batteries in, and it didn't immediately change the input to radio :) All the buttons seemed to work just fine, but I was unable to adjust volume. So I took it down to my workbench, opened it up, and took out the microswitch from the control wheel, and cleaned it with contact cleaner and a toothbrush to get the bristles between the contact points and clean whatever carbon might be on it.

I put it all back together, and started over once again. Still no volume control.

Well, when I was playing around with the other MCP, I was able to adjust the volume from time to time. Not very well, but I could get it to work. So I opened up both, and swapped the microswitch from the bad MCP to the good MCP. Still the same issue. No volume control.

Ugh this is frustrating. I just want to listen to the system, it's been a solid 2 weeks now.

I'm starting to wonder whether the BM should be at fault, or it's very hard luck indeed.

The Beomaster may be at fault for the volume control issues. Admittedly, this is my first Beosystem, and there are things about it that I'll need to learn... So I created a short video to show it off a little and show the issue I'm having. One of the things I've noticed, whenever I get the Master Control Panel's screen on and try to adjust the volume, the screen blinks at me until I stop adjusting the volume. So it very well may be Beomaster related.

I'll put the URL to the YouTube video here... I've been able to edit in YouTube videos, but for some odd reason they never show up in the post, if anyone has a way to help me with that, I'd appreciate it.

https://www.youtube.com/watch?v=TwAhpEQxQWI