It might need a new toggle switch. An easy and not expensive repair!

A $6 part and a few minutes with a soldering iron.

It is quick-disconnect terminal.

Where can I find (buy) replacement switch?  Mine now has the same problem (can’t turn it completely off).

@cs9314 

Measure the rectangle cutout size and find the correct replacement spst rocker switch.

https://www.parts-express.com/electronic-parts/switches/rocker-switches

Got it, ordered two switches just in case I need another one down the road.  I always turn the unit off after using it, so the switch gets used.

 Thanks 

Update to anyone that cares, the replacement switch lasted less than a year.  My unit is not abused, it only gets used maybe once per week so I’m not “wearing it out”.  Always the same:  rocker switch will not click fully in the “off” mode to completely turn off the unit so it doesn’t sit there generating heat even when not in use.  While yes it is an easy fix, it’s annoying as hell to have to pull it out, take off the top panel and futz with the switch repeatedly.  What’s odd is if I pull the switch out of the panel slightly (leave it protruding out the back rather than locking it in place), it will work (solid, audible click and power goes off).  I’m wondering if the factory hole in the panel needs to be ever so slightly enlarged as it may be too tight on the little toggle switch preventing it from working correctly?  Anyone else have similar experience?  BTW, I still LOVE the tone out of this thru my HPM-150’s!  Seems like a great marriage of old and new technology.

 I always turn the unit off after using it, so the switch gets used.

Standby power consumption is less than 0.5W, and it is not necessary to turn off the Azur 851A through the rocker switch on the back.

The unit stays pretty warm (almost hot) if the rocker switch isn’t turned off.  Is that normal?

Sometimes the unit sits for several days, up to and including a week not being used.  

I have a 651A integrated and it remains cold when not powered and the rear panel switch is on.  So, I think you have a problem.

@cs9314 

You can plug the 851A to a kill-a-watt and see if the standby consumption is less than 0.5 watt.