Another channel repair thread

[RideTheCrash]

Okay, this is an update from this old thread of mine (if you want some background information)
http://www.homerecording.com/bbs/sho...light=audiopro

Mixer: Audiopro 16-S (1983)

Problem: Channel 6 has a very weak signal compared to the rest of the channels.

This is kind of redundant I guess, so you can tell me to fuck off...

Is this type of problem only caused by leaky caps (or just bad caps, whatever happens to them)? My father-in-law will do this for me, because he is knowledgable in this area.

I can provide him with the schematics, he has the test equipment, the soldering gun, and the skill. Replacing caps with the right ones is no problem, so I guess what I'm asking is: is there is anything other than caps that would cause this problem? Is there anything else that should be looked for?

Here is part of the insides: http://www.freewebtown.com/smsessions/audioproguts.jpg

Note the previously replaced caps (the darker blue ones). Thanks.

[TimOBrien]

Could be anything. Even just a bad solder joint anywhere in the circuit.

You need to be able to pass a test signal through the channel and then explore along the way with some test equipment, or you'll just be chasing ghosts and may make the problems worse.

Try and find someone in your area (college, high school, etc) who can help you diagnose it.

[RideTheCrash]

Well my father-in-law is just as good as anyone to help me diagnose it. He has test equipment, so I suppose we should do some tests before we start screwing around...

[dgatwood]

Originally Posted by RideTheCrash

Okay, this is an update from this old thread of mine (if you want some background information)
http://www.homerecording.com/bbs/sho...light=audiopro

Mixer: Audiopro 16-S (1983)

Problem: Channel 6 has a very weak signal compared to the rest of the channels.

This is kind of redundant I guess, so you can tell me to fuck off...

Is this type of problem only caused by leaky caps (or just bad caps, whatever happens to them)? My father-in-law will do this for me, because he is knowledgable in this area.

Dollars to doughnuts there's a trim pot in there somewhere that just got turned down or dirty. One of the two outputs on my Mackie CR1604 was low for the longest time. Then, I tore it apart and tweaked the trim ports on the OTTOMIX board and... presto... no more problems.

Either that or maybe a dirty contact where a cable plugs in or two boards plug together....

[RideTheCrash]

Good thinking...

From what it looks like, the jacks on the back (in, out, XLR mic) connect to the channel board via a plug. We had cleaned out the pots months ago, but not that well, just enough to get rid of the major crap in there.

[RideTheCrash]

I actually have a manual in PDF form from Yorkville which has a whole test set up with test equipment to check voltages and other various things. So I think if I take this over and have him check it all out, it should pinpoint a problem.

[RideTheCrash]

Okay I think I figured out the problem.

I was looking on the other side of the channel boards looking for anything that looked different and I noticed that something looked broken off. I believe it is a resistor that is missing. All the other channel boards have it except the problematic channel. I'll get a new one put on, and let you guys know if that solves me problem.

Oh yeah, and I was testing out all the channels to make sure they were okay today, and the fried channel, 9, which I mentioned in the other thread actually works now. I could of sworn it worked once in the past, so maybe it's intermittent problem, we'll see in time. Of course, that being said, the activity light for channel 11 doesn't work and the channel is dead. And the caps have been replaced it looks like in the past on that one. I don't really use that one, so it's alright for now.

[RideTheCrash]

I'm talking to myself, but for whoever is interested:



See the resistors at the top of each channel board? The second board you see is channel 6, which has no resistor. The only part that bothers me, is that it looks like nothing was ever soldered onto that board. I looked where the resistor was supposed to be on the circuit board and it looks clean, like nothing was ever on there to be broken off. But surely if every single other channel has one in that spot, it must be the problem for this channel...