Why do my var doesn't display in its template (sidebar) ?

[Bastien]

I'm trying to integrate my chatbox to the sidebar on the forum

My bloc forum calls my template (which displays well
Chatbox [Archives]
output_template : $output)

my bloc content is :

$output='$output';
return $output;

and calls my template

If I put an echo $output in the forum.php file, it displays well at the top of the forum
But not in my template (whereas I put

{vb:raw output}

and declared the output var at then end of forum.php

$templater->register('output',$output);

I need help plizzz