Erratically relay switching

[Murdock]

My consoles controll room module developed a strange behaviour where the monitor output relais start erratically switching which also leads to crackling sounds in my monitors. The switching is really fast.
Normally I hear the relais switching once a second or two after power on of the console.
What kind of relay circuitry is used here?
Is it a protection or delay circuit?
Any hints on what that might be?

 

[radardoug]

So you dont give us any information apart from you are having a problem, and a badly photographed schematic for something. If relays are flicking on and off, its probably the power supply. If you are not technical, hire a professional.
If you want help, give us as much data as you can. The brand of console would be a good start.

 

[JohnRoberts]

if the relay has a delayed turn on circuit perhaps look for a dried out electrolytic capacitor.

JR

 

[gyraf]

agree - if e.g. your C320 (470/16) dries out a lot, this could possible cause hicckups..

 

[Murdock]

So you dont give us any information apart from you are having a problem, and a badly photographed schematic for something. If relays are flicking on and off, its probably the power supply. If you are not technical, hire a professional.
If you want help, give us as much data as you can. The brand of console would be a good start.

I'm sorry, like I said, I'm just asking for a direction or hint. I didn't write the name of the console because it is pretty unknown. It's an Acousta DCA 100E. There is almost no information on the web...
I was lucky enough to get hold of a few folders with all the schematics.
And I thought this part of the schematic was enough for someone to identify the type of circuit around the relais. I didn't ask for anyone to exactly pinpoint my problem.
The console had a few problems which I could solve myself with searching and experimenting which I'm quite proud of myself because, as you can probably tell, I have no electronics background. And I learned alot in that process. And the only tech who is experienced with these consoles lives in Austria and asks over 100,-Euros per hour. Not that it is too much to ask, but too much for me.

And I'm sorry for the quality of the schematic picture. On my Iphone it was pretty hires. But the site probably compressed it. Will try to make a better picture.

Concerning the PSU as the root of the problem I think it is unlikely because all the other relais in my console are functioning well. And they are all fed from the same line. And the PSU has LED indicators to show if the voltages are correct.

agree - if e.g. your C320 (470/16) dries out a lot, this could possible cause hicckups..

Thanks! Thought about just replacing all the parts of the relay circuit including the relais. But will start with the capacitor.
So it is a delay circuit? To protect the monitors on power up? It is no overvoltage protection circuit?

 

[zamproject]

This circuit section probably have two function, delay ramp at power on as already say, and instant silent cut at power off (faster than PSU voltage fall out).

Acousta is known for broadcast console, and audio line out power turn protection is a basic specification in this field.
When you operate and interconnect equipment in a network constantly active you don't want temporary installation or equipment fail to cause any perturbation, including pop for million listener.

 

[Matt Syson]

Looking closely at that power on delay circuit I am puzzled by it's design. The first transistor has full logic supply on it's collector and the emitter is straight to the base of the second transistor. There is no obvious current limiting mechanism. IF the pull up resistor was a very high resistance value pt the transistors were pretty low gain that might be a (poor) solution. The 'oscillation might be because other mute relays are influencing this because the second transistor is not actually pulling down hard enough. Altogether not a brilliant design.

 

[JohnRoberts]

Looking closely at that power on delay circuit I am puzzled by it's design. The first transistor has full logic supply on it's collector and the emitter is straight to the base of the second transistor. There is no obvious current limiting mechanism. IF the pull up resistor was a very high resistance value pt the transistors were pretty low gain that might be a (poor) solution. The 'oscillation might be because other mute relays are influencing this because the second transistor is not actually pulling down hard enough. Altogether not a brilliant design.

you made me look again... it appears pretty conventional... RC for slow turn on, and immediate turn off when Vcc collapses.... If cap is open AC on Vcc can cause relay chatter.

Diode from base of T1 makes more sense with cathode to collector of T2, old hand drawn schematics often have such mistakes... or not.

JR