need help with schematic please

[ptribbey]

First, can anyone guide me as to where to upload the pdf of the schematic in question.
Then we can get to the meat of the problem.
The malfunctioning electronics is a Behringer Eurodesk SL2442FX-Pro 24 channel mixing board that has an intermittent left main out.
I am leaning towards a leaky cap from past experience. If I raise the input level, the channel will start to function correctly. Please don't reply with a post such as "boy are you retarded,, thats not it.." etc.
I am having a tough time following the schematic as it is in a form I am not familiar with.
I guess what I would like is for some of you talented people to take a look at the schematic (when I post it) and give me a little insight.
Than You
Paul

*for instance*
http://midistudio.ash.com/untitled-12.html

[haklesup]

For uploads, most people have some web space that comes with their email account. If you do then find out from your ISP web portal how to upload then post a link to your personal webspace and file

For example if you had comcast the URL might look like
http://home.comcast.net/~haklesup/microwave_hole.JPG

Capitalization does count. Make sure your link is exactly what you uploaded and spaces in file names are usually more trouble than its worth.

For images you can use a 3rd party site like http://imageshack.us/

I agree with a leaky cap theory being at least somewhat likely. Electrolytics are often the cause of many failures. If you can't find an obviously bulged or vented cap, there are ways to isolate them. However if there are not too many, a wholesale replacement of all electrolytics can often do it.

The only retards here are the first time posters with generic comments and embedded links to commercial websites who think we won't notice their attempts at using this forum for search engine optimization (SEO). Your question is brilliant in that light.

If high input level helps, it may be a passive in the feedback or the op amp in that channel's input preamp stage.

[dyarker]

From info given, my first WAG is a dirty potentiometer.

Cheers,

[ptribbey]

Thanks Haklesup. The schematic is posted to : http://home.centurytel.net/ptribbey/

Upper left corner of pg 8 of 9 shows the left main. I have o'scoped the problem appearing at MAIN_L X35-10. Question I have is where in the heck does that signal come from? I cannot find MAIN_L any where else.
I am fairly sure the schematic originated in Germany.
I guess I just expected to find a lead somewhere in the schematic labeled MAIN_L and then trace back with the o'scope from there.

Paul

[ptribbey]

Dyarker,
Very astute but unfortunately unlikely, as I have twisted [and slid etc.] each and every relevant pot on the board a number of times. These controls contribute no noise that I can detect.
Thank you for your thoughts though.
Paul

[dyarker]

Link you gave wouldn't let me log on anonymously with my e-mail address.

I was thinking more the linear slide pots than the ones you "twist". I suppose you moved those too. Oh well, that's the nature of a WAG; or even an EWAG

[ptribbey]

Sorry, I fixed it from "FTP" to HTTP"
Here is the schematic:
http://home.centurytel.net/ptribbey/

A little more background:
The FX section on the sound board has a test tone feature. I set it up for that on both ch 1 & 2 FX.
So I can dispense with all 24 General purpose inputs as the culprit. It is definitely somewhere between the FX out and MAIN_L in.
Also the in and out 1/4 in jacks have switches in them. I have ohm'd out ALL of them and o'scoped the relevant ones. They are all functioning correctly to the best of my knowledge.

My original question was to help me read the schematic. I'm still not finding where the signal to Main_L on page 8 of 9 comes from. Any ideas?

Paul

[haklesup]

Look at page 4 of 9 right hand side middle just above and below the Tape out jacks.

ofetn I have to physically trace signals in the hardware to confirm how a schematic is routed. Occasionally the style of the draftsman or peculularities of the CAD system make a schematic harder to read than it needs to be. MultiPin Connectors, multi pole switches and terminal strips are often the hardest to read especially if their sections are spread over several pages.

With a PDF, you can run the OCR then use the text search to find labels. In my version of Acrobat its the Document menu and the Recognize text using OCR command. The search box is on the toolbar on top of the window. You can also add various color highlights and comments to your PDF as a way of tracking your progress

[ptribbey]

Thanks so much haklesup.

Paul

[ptribbey]

I found the problem to be failed mute switch SW21C on page 4 of 9.
Turns out my leaky cap guess was incorrect. oh well.

Thank You to haklesup and dyarker for your assistance.

I learned about OCR on a pdf schematic and I am guessing it will save untold time in searching for things like "MAIN_L"

Paul

[haklesup]

So did you clean it or replace it?

[ptribbey]

I cleaned it for now with CRC 2-26 Precision Lubricant.
Sent message to the owner on what they want to do next.
What a pain to disassemble that board from the faceplate. 62 pot knobs, 9 fader knobs and a bunch of screws.

Paul