Before I watched your video my suspicion was that maybe you had inadvertently set the meter ballistics to "slow"...
But after seeing what's going on, man...I don't know, and I'm not all that familiar with Amek desks... @Boswell ? @Kurt Foster ?
And didn't we have an RO Member who was rebuilding an Amek console a few years back? Was it Joel? @Asaf Smilan ...
Is this happening every time you stop signal? Or is it intermittent?
Has this been happening for a while, or did it just start?
Are you noticing any other issues... Noise? Hum? Any sudden increase or decrease in signal?
Assuming you've made no recent mods or other repairs to the desk...
Just thinking out loud....
Double check the phantom power is working properly, problems with the two matched resistors can mean there is a DC imbalance and the input meters are seeing voltage, which eventually discharges via the capacitor and the meters return to normal. Unlikely to come and go, but if there is a switch to turn it off try it. Had this on a soundtracks desk in the 90's. You can get the same effect when you connect a sub mixer that has phantom accidentally turned on.
There are several significant observations to make about the behaviour of the metering shown in the video.
Firstly, all the channels are affected, so that, for example, it's unlikely to be a phantom power problem on any one channel.
Secondly, the fault gives similar, but not the same, magnitude of effect on every channel, and corresponding decay times.
Thirdly, there are not many places in a complex analogue system such as the Amek Angela that have time constants of order 1 minute.
The initial suspect area is the power supply rails, as Paul suggested. I've not been able to find any Angela schematics on line, so a guess would be that the design of the metering section is not proofed against variations in the internal power rail voltages.
A cause of the problem could be leaky reservoir capacitors, or high-impedance contacts at the rectifier diodes or at the voltage regulators. If I were sitting next to the console with its lid removed, I would put a digital voltmeter on the power rails feeding the metering board and see how much variation in rail voltage could be invoked by feeding a signal generator or some loud music through many channels at once.
If you accidentally apply power to a Soundcraft mixer (the one I was using was a Live 8-32) input - I had it's output plugged into channels 1 and 2 of a Yamaha, with phantom turned on accidentally - and all the Soundcraft meters, including the groups all lit up to the same level. sticking power up the output of a mixer I can imagine causing problems in the output section, but it managed to get to every channel. The cause of this fault will be a strange one. The trouble with phantom power is that any fault will be applied to one point on the desk, but once it's there, it can spread because all the channels share so much - the axes and groups, PFL lines and stuff like that. A fault in the master section could leak back through the grouping on old style desks. I had an old Mackie desk years ago that when you turned the power supply on - every meter kicked and fell gently back. Much defy common sense.
Watching the video also shows that while music is playing leds stay on longer then they should between the individual channel peaks....if you have music only one channel does any other channel leds turn on?
I've already replaced all the electrolytes on the meters PSU and it doesn't made any change.
Since this problem is happening in all channels / meters can we say that the fault happens before the meter circuits?
Attached the schematic: https://i.ibb.co/jgD34qy/angela-meter-schematic.jpg
At this moment the console is installed in a way that preventing me from access to the meters PCBs ant to the power distribution board.
Next time I'll have access to those parts I'll start by checking the diodes and resistors on the power distribution board?
The meter circuit you posted is not capable by itself of creating the sort of fault you report. That means you have to look a bit further afield. Do you have the schematics of the remainder of the mixer and its power supply?
I have the schematics of the input and master channels, but I don't have the meters PSU schematic.
When I've measured the voltage coming from the meters PSU it seems to be right.
I've also noticed that when I'm turning off the meters PSU the positive voltage LED indicator on the PSU panel turns off immediately while the negative voltage LED indicator turns off after 10 seconds.
When I'm disconnecting the meters PSU from the console, both LEDs turns off together after a minute or so.
In the first part of your video when you had the control cable connected to the console, was the console powered or unpowered? The behaviour in the second part (the meter circuit unplugged from the console) I would consider completely normal.
The implication is that the positive rail of the meter PSU is back-powering some of the circuitry in the console. Without access to more schematics, it may be difficult to take this any further, including forming an opinion on whether it is related to your original problem of the meters not returning to zero in a reasonable time.
Thanks, I've set it for about +12V.
Now what other schematics you would like to see that can help you to understand this problem (the too long decay time of the LEDs)?
I have the schematics for the input channels and for the master channel.
Would it help?