LED Peak indicator blinking while no signal

[Studiogearlover]

Hey Guys..i have a wonderful broadcast mixer (Gentner) from 1989, 4 channels sounds great, got it used... (for 50 bucks). However, there are few little things are going on while I was testing this. I would like your expertise on this. What is happening:

- Mixer turned on, only on channel nr 3 the peak led indicator blinks momentarily, after like 20 minutes the mixer is on. No signal passing. While blinks, no distortion or anything coming out of the mixer. Seems that the peak LED indicator has its own life...

- while switching off, i hear a high sweep ish noise, with a little pop, few of the LED indicators pops up, some in red some in green. Not sure if this is normal or tend to be like this, it seems a bit harsh to me .. not enjoyable when your power amp and speaker is on.

Maybe the two issues above are related to each other? Overall the mixer is super nice... however, the above are bothering me a bit..

In case you had similar issues with any of your audio gear, please share your solutions/problems! Cheers!

 

[dmp]

- Mixer turned on, only on channel nr 3 the peak led indicator blinks momentarily, after like 20 minutes the mixer is on. No signal passing. While blinks, no distortion or anything coming out of the mixer. Seems that the peak LED indicator has its own life...

Bad connection or cold solder joint possible

- while switching off, i hear a high sweep ish noise, with a little pop, few of the LED indicators pops up, some in red some in green. Not sure if this is normal or tend to be like this, it seems a bit harsh to me .. not enjoyable when your power amp and speaker is on.

Always turn off or mute the power amp first. Or, add on a relay mute circuit on the main output that quickly switches to mute on power down, if it is important to you.

 

[Studiogearlover]

Thanks DMP! Appreciate your help. The cold solder or bad connection...around the actual led indication right?

 

[dmp]

Yes, I would look at the peak indicator circuit and make sure it has good power and ground.

 

[JohnRoberts]

sweepish (?) noise could be some HF oscillation. Generally we can't hear the HF directly but some rectification in slower circuits.

Can you benchmark the different channels and look for an outlier (channel behaving differently).

JR

 

[emrr]

I saw this on a late 90's piece, increased until it became apparent it was the PSU failing, shutting down, coming back on, shutting down.

 

[Studiogearlover]

Thanks JR and Doug! All the channels sounding identical. No difference... the funny thing is this peak indicator comes on after like 20 minutes..and then goes away on its own.. and back after an hour or so...cleaned the pots and will open up tomorrow to see inside again..last week I did check the PSU, seemed ok..i had +15, -15, +5 and -5 ( if I recall correctly) and the phantom is 30 VDC on each channel.

The PSU caps are still original, IC caps, looked OK by sight and kinda high quality... Thanks guys!

 

[JohnRoberts]

old electrolytic caps are always suspect... could be leakage putting DC somewhere it shouldn't.

JR

 

[Studiogearlover]

Roger that... will check them with my ESR meter. Difficult access will be... the funny thing is that when these peak indicators are blinking with no sound, I would expect some nasty buzz or something coming out if that channel...but nothing.. super clean even if the peak led in red and blinking.. puzzling!

 

[Studiogearlover]

Guys..i think some more to this than an LED issue... i am puzzled. Opened up the mixer, checked the associated caps with each channels, cleaned the pots again with contact spray. All the caps were low ESR and within tolerance. However something really odd is happening. When I tried to plug the 3 prong AC cord into the back of the mixer for testing ( mixer is off of course) my table lamp went off?!? I did try several times and it does it again and again... how on earth this is possible? The fuse is not blown and my table lamp is also fine. But as soon as plug the IEC socket at the back of the mixer, shutting off my table lamp... is that power filter IEC is failing? I have not see anything like this.

 

[Bo Deadly]

When I tried to plug the 3 prong AC cord into the back of the mixer for testing ( mixer is off of course) my table lamp went off?!?

That is weird.

The only thing I think think of off-the-cuff would be that maybe somehow mains neutral has been connected to earth and the parallel connection of the lamp and mixer causes the load to double back through the mixer to earth. Y capacitors are designed to fail open though so that shouldn't be.

Is the mixer on when this occurs? If not, does it come on when you unplug the lamp?

Another possibility might be that there is resistance in the mains line somewhere and the extra load is causing the voltage to dip just enough to cause the lamp to drop out. Are you running off grid with batteries and inverter and the lamp is LED ... etc?

 

[Studiogearlover]

Thanks Bo.. no off grid...i am using the mains socket from the house goes into my extension lead of 3 sockets where the mixer, the LED desk lamp and my power amplifier plugged in. The above happens when the mixer switched OFF and plugging in the IEC plug at the back of the mixer... i will go further tho: The mixer is off but plugged into the mains and only my power amp is on, HUUUGE buzz is coming out of my speaker. Something is not right here... the only reason I was suspecting that IEC EMI filter as that this is the only thing is connected when all of the above "syndromes" are happening. The mixer circuit is switched off... just scratching my head really now. This is something very very odd...

The house AC socket seems to be correct, checked with a tester and has a good ground. 3 prong AC cord is also good. I need to get hold of another EMI filter socket, although it does not look burned or anything from outside.

 

[JohnRoberts]

What happens if you shift which socket the lamp and mixer are plugged into...?

Something sounds dicey and manis power can kill you so be careful.

JR

 

[Bo Deadly]

... mixer is off but plugged into the mains and only my power amp is on, HUUUGE buzz is coming out of my speaker. Something is not right here... the only reason I was suspecting that IEC EMI filter as that this is the only thing is connected when all of the above "syndromes" are happening. The mixer circuit is switched off...

That does sound like it could be a short Y cap in the mains filter which is precisely what Y caps are not supposed to do.

 

[Studiogearlover]

Thanks Bo, and thank you guys. Ordered a new EMI filter inlet, will not turn on the mixer until the new part installed. Fingers crossed this will solve it. I will come back and share the result later! Cheers guys !

 

[Studiogearlover]

Alright... update! The new EMI filter arrived, installed and.. still doing it. I decided to swap my LED lightbulb on my desk...and guess what...its not doing it anymore. I am still puzzled what phenomena was this...anyways.

Mixer is good, not doing the initial peak indicator blinking anymore either...one thing tho I would still ask you guys I am sure you know about...these 4 channels and the indicator lights...so when signal in OK gain is green and when peaks, its red..its like any everyday mixing console but each time the LED shuts off i hear a little tiny pop in the audio signal.. I am not sure this is a normal thing of a mixer retailed at ~1500 USD in 1989, all TX inputs ( looks like Belclere )... is this solve-able somehow as I am not sure this way can be used in professional audio situations, and this one was made for that... could you please help me with this? Many many thanks! ..i really want to save this baby.

So basically i am only hearing a pop when the level indicator led- after a signal triggered it- turning off... its like when you are using a gate and when the gate goes off due to no signal, makes a pop when switches off... i hope its not too complicated how I describe it...

 

[Bo Deadly]

Alright... update! The new EMI filter arrived, installed and.. still doing it. I decided to swap my LED lightbulb on my desk...and guess what...its not doing it anymore. I am still puzzled what phenomena was this...anyways.

Sounds like there is some unshielded circuitry and it's sensitive if the lid is off and maybe a bit even if the lid is on.

Mixer is good, not doing the initial peak indicator blinking anymore either...

That's strange considering you haven't really done anything.

one thing tho I would still ask you guys I am sure you know about...these 4 channels and the indicator lights...so when signal in OK gain is green and when peaks, its red..its like any everyday mixing console but each time the LED shuts off i hear a little tiny pop in the audio signal.. I am not sure this is a normal thing of a mixer retailed at ~1500 USD in 1989, all TX inputs ( looks like Belclere )... is this solve-able somehow as I am not sure this way can be used in professional audio situations, and this one was made for that... could you please help me with this? Many many thanks! ..i really want to save this baby.

So basically i am only hearing a pop when the level indicator led- after a signal triggered it- turning off... its like when you are using a gate and when the gate goes off due to no signal, makes a pop when switches off... i hope its not too complicated how I describe it...

So now you're on to a different problem entirely.

To properly diagnose the health of this device you probably need a scope and a schematic. Do you have either?

 

[Studiogearlover]

sadly no... i dont have any of those... schematic for this device is non existent it seems as it was only a few ever built/sold for whatever reason... the thing is that it sounds so good.. only this little pop noise as explained above. Maybe a stupid question but would an isolation TX solve anything as this is within the audio path or...it does not work like that... i am not really a techy tho... thanks for your input!

the initial problem ( red led blinking when no sound) i think it might had to do with some in depth cleaning...went on with the contact spray on all pots again... OR the EMI filter was kind of faulty indeed as that is the only thing was changed... It is difficult as I do not have any history of this, only that belong to a radio station in Ohio..thats all i know and whats inside by the look of it and I have a leaflet advertised with the price tag on it..

Really thank you for taking your time and help...