Behringer Vintager AC112 : cloc and silence ...

[Django29]

Hi.
My amplifier Behringer AC112 becomes completely silent after 1 ou 2 mn of work, and a big "cloc".
It's not the lamp because I changed it, and it's not the pre-amp because it doesn't work neither by the aux in.

Any suggestion ?

[J M Fahey]

Start by asking for the schematic at Behringer and post it here.

Say you are a Tech, a Customer brought one, serial number xxxxx , and that you need it to proceed.

[nosaj]

Start by asking for the schematic at Behringer and post it here.

Say you are a Tech, a Customer brought one, serial number xxxxx , and that you need it to proceed.

Go here https://music.secure.force.com/Suppo...hringer&rt=gnt
It works I have gotten service manuals for behringer at that link.
model and serial number required.

nosaj

[Django29]

Thanks guys. I just asked the electronic diagrams to Behringer. Hoping an answer.

[Django29]

Hi. I got the electronic shematics (attached), but I must admit, although I was an electronic engineer, I have no oscilloscope to look for the deficient component. Just a voltmeter.

Ac112_SCHEMATICS_Rev_F.pdf

If someone has a suggestion ...

[J M Fahey]

Thanks for the schematic.
Sadly, I think you will need an oscilloscope, not for it to show you the bad component, it does nit work that way, but to inject an audio signal at the preamplifier input and follow it along the amp, from said input to speaker out and speaker itself, to find where it gets lost.

Problem is, this amplifier , at least from what´s shown in schematic, has a ton of ribbon wiring jumping all over the place plus needed connectors at both ends, so you have four opportunities each to lose signal simply because of poor contact: both female ends and matching male pins at the PCB.Multiplied by the amount of ribbons.
Simply one which is poorly seated or half unplugged because of road bumps or similar is a possible cause of signal loss ... even if "parts" are fine.

Add that they also use many electronic switches, "audio gates" if you wish, to switch channels, change EQ or distortion, etc. , based on a CD4053 triple SPDT switcher.
And it has lots of "mute" lines crisscrossing it.Oh, and they skipped the Digital Effects section.
Amp may work very well, the digial section fail or simply be disconected or be crazy and decide to stop after 2 minutes and we have no clue about that.

Yet my point is that the amplifier is fully repairable (except the Digital section) , but it will probably be slow and boring, testing one after the other the lots of points where signal may get lost.

To start with something, and using the "divide and conquer" method, trying to isolate the problematic block:

1)

and it's not the pre-amp

well, you have not really confirmed it works, but for now we´ll leave that for later.

2)

because it doesn't work neither by the aux in.

Doesn´t work at all or works and mutes after 1-2 minutes?
Not the same.

Inject signal (some MP3 from the smartphone is fine but beware, some smartphones are "too smart" and self mute if they do not detect an earphone, so check it´s actually putting Music out ) , set Aux gain to 5 , set Master Volume to 5, you *should* hear Music through the speakers IF it worked normally.
Please describe what actually happens.

[Django29]

Thanks a lot for your help JM !

I just stripped down my amplifier, and the only thing I did is to unplug and reconnect a connector between the preamp and the amp. (impossible to add the picture I took, for any weight of file :" ... exeeds the quota ...").

Then I plugged my guitar, and it seemed to work. After 15mn, the problem was not back.

I hope it will last, but the next time I go on stage, I think I will use my other amplifier (Peavy "Special", 40 years old, never a problem).

I appreciate a lot you took the time to give your opinion on my problem.

Bye..... (if the problem doesn't come back...).

[Django29]

BIG disappointement. After I put the amplifier together again, I plugged my guitar, and as before, after 1 or 2 mns, a few big "clocs", and silence !

So back to 0.

[J M Fahey]

Maybe back to 1 but definitely not to 0

We now know preampworks, power amp basically works, you have some interconnection or "mechanical" problem, or, maybe, some cracked solder.

Hey, we reduced 20000 possibilities to just 2000

Pull chassis out again (yea, I know ) and retest.

IF it works, do not put it back BUT get a chopstick, plastic BIC pen or equivalent (hint: insulating material) and while playing some continuous music or tone, lightly tap all over the place, including parts free board areas, all components, all wiring, connectors, pots, switches, jacks, etc. , lightly wiggle all wires, to check whether you can make amp cut off or not.

There are more tests but first is first.