I also have an old vintage holy grail that has the exact same problem. I bought this pedal new about 15 years ago and love the sound.
I really like the spring setting and would love to have it back to working again.

LED light comes on when plugged in with original factory supplier power adaptor.
In bypass mode the sound passes through just fine.
After hitting foot-switch, there is no discernible reverb and after turning the knob half way, the sound is attenuated and reduced.
When turned to the maximum / all the way to the right, the sound goes away completely.

I am a little confused since it looks like Newpantera submitted 1st post, and then answered his own post 2 times.
This makes me wonder if it was someone else who posted the 1st Reply.

Hi, EHXMan,

Could you please weight in to let me know if this failure is worth repairing?
Could it be something small like a resistor?
Or is it more likely something major like a processor chip?

Any help will be appreciated.

Thanks!