Attenuator bypass?!?

[Davebassman]

A strange thing happened to me today with my amp and my attenuator. Usually I use an attenuator at home, and sometimes I like to push up the volume for overdrive. And suddenly, it's like the attenuator bypass him... and don't actuate over the amp... I can't regulate the atteunator volume knob, he goes from no sound to a full sound.

Anybody can explain what happen?

[Helmholtz]

The attenuator might have lost a ground connection. But how could we really know without seeing what's inside the attenuator or having a schematic?

[Davebassman]

It's a Harley Benton power attenuator. This is the schematic:

https://blog.brixit.nl/static/image/hbpa/schematic.jpg

https://blog.brixit.nl/blog/2016/2/h...-and-teardown/

[Helmholtz]

I would start with checking all ground connections with an Ohmmeter. Should measure below 0.5 Ohm with a calibrated meter.

[Davebassman]

The grounds seems okey.

I measure the resistance of every input:

4Ohm:
lpad min: 8.3R
lpad max: 16.6R

8Ohm:
lpad min: 12.3R
lpad max: 20.6R

16Ohm:
lpad min: 16.3R
lpad max: 24.8R

[Davebassman]

I think that I solved. The switched jack from 16Ohm are always open. The attenuator was always at 16R!!!!

[Helmholtz]

Seems the "L-pad" (actually a simple power pot) is not properly grounded.

[Davebassman]

I replaced the switched jack from 16Ohm, and now I have this readings:

4Ohm:
lpad min: 4.2R
lpad max: 5.7R

8Ohm:
lpad min: 8.5R
lpad max: 9.8R

16Ohm:
lpad min:16.3R
lpad max: 24.4R

[Davebassman]

I disassembled the lpad and it's burned...

https://ibb.co/rf9GbrP

My amp is a Bassman aa864 50W I can use this Attenuator no?