Amek BC1118 schematics needed

[Cosmonaut]

I'm working on this console and two of this modules are operating faulty, one of them  has something wrong in the eq section, when you press "eq in" the signal in the left buss dissapear. I tried to swap the TL072 but something else should be wrong. The other faulty module is having like medium gain always (the gain pot only change the overall gain a little, and does not attenuate the signal completely), something should be wrong with the feedback resistor or caps with the pot, but a schematic would be really helpfull.

I have the manual of the console, but I only have schematics for the psu, any help would be great.

Thanks in advance!

 

[mjrippe]

For second problem, replace the pot?

 

[pucho812]

do you have the schematics? should make it much easier to track down the first problem. You may need to recap due to age.

 

[Cosmonaut]

The schematics is what I need, I would recap the whole eq, but need the schematics...anyone?

 

[pucho812]

hmmm shouldn't need scematics to do a recap.  Although if they did a value changes that are different then the schematic would not reflect that.

 

[Cosmonaut]

Thanks for the responses, tomorrow I wil buy some lytics and try it...I hope the styroflex are ok because these ones are not available locally.

With the other module, I was suspecting about the gain pot also, but I'm measuring with the component tester of my oscilloscope and is not so different to the other channels, curve changes the same with pot movement as the others. I'm thinking that if a cap is not blocking DC from/to the pot something strange like this could happen, or maybe a resistor in parallel with the pot out of value could do this also...well I think with the schematic would be much easier.

 

[Cosmonaut]

Everything solved with the channels, thanks guys, next time I will recap first, ask second.

For future readers:

-EQ problem: recapping the whole eq area ( 5x 100uf, 16v and 22uf,35v) solved the problem.
-Gain problem: finally I was right! the pot was ok but one of the caps was leaking DC in to the pot making the TL072 unstable.

Thanks! now I just need a new fader for another channel and call it a day.

 

[gyraf]

Any chance you'd find a schematic for this, that you could share? (Amek BC-II, BC1118 Stereo input module)

Jakob E.

 

[mjrippe]

Everything solved with the channels, thanks guys, next time I will recap first, ask second.

For future readers:

-EQ problem: recapping the whole eq area ( 5x 100uf, 16v and 22uf,35v) solved the problem.
-Gain problem: finally I was right! the pot was ok but one of the caps was leaking DC in to the pot making the TL072 unstable.

Thanks! now I just need a new fader for another channel and call it a day.

Thanks for sharing the solution!  So funny that the pot was OK.  I was working on a preamp recently and was convinced it had a problem in the feedback circuit - turned out it was the pot!!!

 

[pucho812]

I have had it both ways.

I have had pots broken due to a heavy hand and seem plenty of caps look o.k. but are dead or leaking or any number of other things.

 

[Cosmonaut]

Any chance you'd find a schematic for this, that you could share? (Amek BC-II, BC1118 Stereo input module)

Jakob E.

Sorry Jacob, I have no schematics, I did a "blind" recap ...also I send a pair of mails to people who usually works on these ones, but no answer, I only have the psu schematic if you need it.

 

[gyraf]

Thanks - I have the PSU.

Uploaded the PSU and the BC1115-1116 mono input module to TechDocs/Amek: http://groupdiy.com/index.php?topic=44846

Also, I managed to find a schematic of the BC1145 Aux module. Will upload when I eventually get it down to size (they're camera snapshots because the large size originals)

Jakob E.

 

[Cosmonaut]

New problem in the Amek:

-Another BC1118 is producing like a wind noise that is always present in master buses and auxes, the only things that makes the noise dissapear is when is totally right panned. The noise doesn't change with any pot, gain or whatever, and the level is always the same (loud!).

Maybe more electrolytics? Maybe bad ground connection?