I reheated some of the big solders on the power supply pcb, and that seemingly did the trick. Can't be sure just yet, but after pulling the cord and replacing it several times with the red led lighting up every time i feel confident that a dry joint was the culprit.

The stand still doesn't park though. I tried programming 1 and 2 a couple of degrees to the left and to the right, but nothing happened when i tried them. 

Good to hear that you fixed the Avant!

But the Beocenter 9300 isn’t yours anymore

Its good to hear that the re-soldering of some of the joints on the power supply module appears to resolved the problem with not switching on.

Going back to the stand issue, if you look at the block diagram below, there are three modules involved with controlling and driving the stand motor. The microprocessor on PCB14 (Only P20 shown on the left) actually tells the "Motor Stand Control" what to do and we know this is working because you can move the stand manually with the left and right arrows.

The problem you have is going to be caused by either:-

1. The "Motor Stand Feedback" module (PCB81) not producing the position feedback signal at pin 6 of P102 OR;
2. The "Motor Stand Control" module (PCB80) not passing the position signal through to pin 2 of P180 OR;
3. The microprocessor on module (PCB14) is not receiving and/or storing the position information which should arrive at pin 4 of P20 on PCB14

The signal which should be received back on pin 4 of P20 takes the form pulses for each degree of movement, if it receives no pulses, then it will store zero movement which is basically what you have. If you have access to an oscilloscope, then I would suggest you monitor pin 4 of P20 on PCB14 and manually move the stand to see what you get. If you do not have an oscilloscope, then the second best thing to do is monitor using a multimeter in the AC range and watch for voltage when you manually move the stand. This second method will not tell you that the pulses are correct, but it will show if a signal is being generated or not.

If the signal is not being generated at pin 4 of P20 then check at pin 6 on P102 on PCB81, if no signal here then the fault is going to be on Module 81.

If however, the signal on pin 4 of P20 on PCB14 appears to be good when moving the stand, then the fault is going to be on the AV and microprocessor module PCB14 and if this is the case we move into a much more complex area.

So, once you have been able to establish the status of the feedback signal, we should be able to determine the next step.

mhw:

Good to hear that you fixed the Avant!

But the Beocenter 9300 isn’t yours anymore

 Haha, will update my signature.
 

Whats the status on the stand ?

I'm working on it right now. I'm measuring changes in AC on pin 4 when I move the stand. I don't have an oscilloscope at home, so i have to make due with the trusty old multimeter.

 

I noticed something. If i turn the stand to one of the sides, then use the remote to turn it the other direction, it will not turn all the way in one operation. It stops some places, and I need to push the button again to make it turn further.

Correction: If I keep holding the button, the stand will continue after about a second.
 

Given you don't have an oscilloscope and also the statement you made in your last post, I suggest you remove the wire from pin 2 on P180 on the Motor Control Motor and if the symptoms remain the same, then we can assume the position signal is not working.

I've cut the position feedback wire, and now when i turn the tv on, the stand turns left for a while and then stops. If I turn the stand manually to one of the extreme positions and turn it back with the remote, it only stops once. Somewhere around half way. I guess this is timed, or my set must be haunted!

I think it is timed by the microprocessor and based on what you have said and tested it seems that the microprocessor is not receiving pulses back with the movement, so when it times out, it stops.

I think you are going to need to look at the position sensor first.

I have a regulated power supply in the workshop on campus. I'll pull the stand-motor-box-thingy () from the TV, bring it there and hook it up to an oscilloscope. Do you know what the pulses should look like?

VICTORY!

It turned out that the gear that was supposed to turn the variable resistor in the stand was broken, and did not turn the resistor when the stand turned.

 

I applied some glue, and now it parks beautifully.

Very well done, now you have a fully working AVANT

HOORAY!!

Yaaaaay! Thanks for all your help along the way, guys!