Check for ripple on the three large filter capacitors.
They have started to die in large numbers now.

If fine, check for DC on the speaker outputs.

Martin

OK, thanks. Those big caps are scary!

Is there a sensor in the cassette deck that tells it there is something wrong? That makes the most sense, (that's what I was fixing) and also the "!" is on all the time.

jhhl wrote:

Is there a sensor in the cassette deck that tells it there is something wrong? That makes the most sense, (that's what I was fixing) and also the "!" is on all the time.

There is a sensor telling if the tape is running.
But it's only active during play/record/FF/RW.

Has the turntable completed its stop sequence or is it running?

Martin

Hi Martin!
 I took a new look inside today and it turns out the T1A fuse has blown - so I've ordered new ones.
I suspect that's all that's wrong.  Does that sound right to you? I hope so! I miss my Beocenter!

If I had lots more equipment and a shop, I'd probably recap it, but I think it might be OK. 

Fuses usually blow for a reason.
You can replace the fuse, but if it blows again - and there's a good chance of that happening - the reason will have to be found and corrected.
My bet is on one of the large capacitors having shorted.
Or the smaller capacitor (220uF If I remember correctly) on the processor board.

Martin

Thanks! I replaced the fuse, but there's not much improvement. Although the LEDs are correctly working when switching between the redo settings, tape and phono, none of the motors (or radio for that matter) do anything, probably being protected by the relay. 
I'd need to get a scope  to check if the caps are bad and to see if there's DC as you mentioned. Is there anything else simple I could check that might be making the relay cut off? It was not displaying any of this kind of behavior until I did that cassette fix.