AI is pretty good troubleshooting help on this ART MPAII

[CoolCat]

heres one with No leakage...go figure?

 

[CoolCat]

this one has leakage? how strange....is this even a real problem or a "loose QC tolerance "

25:35....and he has Channel 2 completely Off, and Channel 1 only but both LED' show dual channel....is what Im seeing.

 

[Steenamaroo]

Yeah, there's plenty of videos showing the unused side being completely dark,
so it's not a design or from-factory issue.

Common fault, though? Seems like.

"Seems the design doesn't keep the unused side OFF"
No, the design does. Some failure is happening.


"Why didn't they just have two separate Ch1 and Ch2...? why tie Ch1 - Q1 to Ch2- Q2?"
Because the controller dictating which LEDs should light up (not which bank...how many) has 8 channels.
To do it your way requires a 16 channel chip, or two chips... = $$


"I don't understand why Q1 is connected to Q2 input?"

Q101 opens and closes rapidly.
Doing so closes and opens Q102 rapidly.

Q101 being open lights ch1 LEDs and closes Q102.
Q101 being closed kills ch1 LEDs and opens Q102.

It's just two switches - one dependent on the other.

 

[CoolCat]

Yeah, the key thing to get is that in proper working condition, banks 1+2 do not light up at the same time.
It just looks like they do, because they alternate fast.
If I sped up my simulation to a few hundred hz, it would just look like both meters were lit a the same time.


With that knowledge you can work out that Q101 is the switch that turns on and off channel 1.
and it also also turns on and off Q102.

When one is open the other is closed, and vice versa.
LEDMux is the trigger which rapidly switches to control the whole thing.


By design, when LEDMux is 0V, Q101 passes which
1: Lights up channel 1
2: Lifts Q102 base, closing it, and turning off channel 2

then when LEDMux is 5V, Q101 shuts which
1: Kills channel 1 LEDs
2: Lowers Q102 base (by cutting off 5v to it) which lights up channel 2.

Knowing that ^^ you know there should only ever be 5V available at Q101 collector (for LEDS CH1) or Q102 collector (for LEDS CH2),
but never both.

This makes sense, thanks. good explanation imo.
ov...Q1 passes to turn on LED
5v...Q1 closed and turns off LED...because its tied to Q2 this opposite effect opens Q2 a little bit and weak LED are ON.
happening really fast so , yeah, good refresh on basic Transistor workings.

so/? when both channels are receiving Sound/Signal....the bleed is still happening on the display, but the Active is so much brighter , the "ghost" isnt seen, I suppose.

this is a good thing really because I don't care if its cosmetic, and Im only concerned something is failing and will continue to get worse rapidly.
it seems there's a bunch of leakage ART MPAII out there but most owners probably don't care.

Would reducing the 5V weaken the circuit enough to not show enough leakage to turn on the unused channel?

 

[Steenamaroo]

0v...Q1 passes to turn on LED
5v...Q1 closed and turns off LED...because its tied to Q2 this opposite effect opens Q2 a little bit and weak LED are ON.
happening really fast so , yeah, good refresh on basic Transistor workings.

Not quite...I'm describing how the circuit works properly...Not the failure.

Q1 closing fully opens Q2.
Q1 opening fully closes Q2.
There's only ever one bank of LEDs illuminated at any given time.

That is the intended function of the circuit.

(To make matters more complicated I've used the terms "open" and "closed" backwards quite a lot. )



The fact that you get full bright LEDs on both channels when you're meant to says that the transistors are allowing current when they should.
So that means current is getting around, or through, both transistors when it should not.

CH1 is fully lit when it's meant to be, and CH2 is partially lit at the same time...It should not be.
(and vice versa)

I don't see a common way around so either both transistors are failing to fully block current, or the signal controlling them is not doing what it's meant to do.

 

[CoolCat]

very strange, so by design it looks right, ok.

but by operation the circuit is leaking, both transistors partially On , with V at the collector.

I wonder if Brand New units have this odd- "ghost" LED leakage.