I have an ITP180B that the maximum volume has suddenly gone down. The volume we used to get at 25 on the scale is now barely there at 40 on the scale

The main board controls the volume. You can get a new one here:
TV Parts Universal TV Stands DLP Chips ShopJimmy

Volume in modern systems are controlled by a single IC. If that goes, it makes the volume functions go wonky. The IC can be found by tracing the wires from the volume control, or following the circuit if it is mounted on a PC board.

Look for a volume control in your settings section. Sometimes the settings volume is down & the app volume is a secondary control that can only go as high as the settings(or master) control, Turn it up and you regain control from the app you are running.

Most likely, your unit is shutting down due to overheating. You cannot run an amp at that kind of volume very long. It is shutting down to protect itself. Try running the amp at 1/3 your normal level. Most likely, it will not shut down.

i have an akura combi and the sound has just gone off , the remote is going up and down the volume scale but still no sound, please help.

Check the volume level first after then also check the audio settieng may be audio level is set up mahually low .I hope it will help you

You can use the PREFERENCES menu option to change the volume of the voice instructions. Use 'Volume preferences' , with its sliding scale to set the required volume in increments of 5%.

The 'Test' function is a good way to get the volume right before starting your journey. You may also find it helpful to use 'Link volume to car speed', so that the voice instructions get louder as road noise increases and are at their quietest when you are stationary.

could have shorted coil, check resistance on each speaker and compare, should be rated @ 4 or 8 ohms, or disconnect both then run individualy to test output

This type of calibartion is known as a logarithmic scale.
The numbers refer to decibels below the maximum output of the amplifier section of the reciever, or decibels of attenuation (making smaller/quieter).

Without going through logarithim theorey, the logarithim (base 10) of 1 is 0. So if 1 is the maximum output of the amp, as you turn the knob down from maximum you are adding more and more attentuation to the output (relative to maximum) and so the loudness of what you hear goes down, even though the number on the scale is going up !

Most peolpe associate decibels with sound levels, but anything can be measured in decibels, so long as there is soemthing to reference it against.

bad solder connections and or dirty controls.