where to start troubleshooting - board/mixer problems, etc

[themagicmanmdt]

so, got my board wired and ready, finally. and there's two problems:

one:

two channels (2 and 9) don't give me any sound input. what's the best way to find where the problem lies? i've opened up the board and done a visual inspection - everything is soldered well, nothing's touching ground, no caps are blown out. i don't get any sound, not even hiss. hmm.

two:

there seems to be a problem with the summing card. i can send audio to all of the busses and get output there, however, no sound gets to the stereo out/2tk. however! if i engage a specific stereo bus on just one or two specific channels, the audio gets to the master outputs!

strange.

i've rechecked molex connections, and there's no funky mods to the board (it's all stock).

what should i try?

opamps? do either of these seem like a bad opamp problem?

is there a particular place in the cards that i can test for correct voltages?

-mt

[RodC]

Do you have a schematic? Does the buses have inserts, are the missing signals on the inserts?

[Nick Sevilla]

so, got my board wired and ready, finally. and there's two problems:

one:

two channels (2 and 9) don't give me any sound input. what's the best way to find where the problem lies? i've opened up the board and done a visual inspection - everything is soldered well, nothing's touching ground, no caps are blown out. i don't get any sound, not even hiss. hmm.

two:

there seems to be a problem with the summing card. i can send audio to all of the busses and get output there, however, no sound gets to the stereo out/2tk. however! if i engage a specific stereo bus on just one or two specific channels, the audio gets to the master outputs!

strange.

i've rechecked molex connections, and there's no funky mods to the board (it's all stock).

what should i try?

opamps? do either of these seem like a bad opamp problem?

is there a particular place in the cards that i can test for correct voltages?

-mt

Hi,

1. What brand, if any, or mixing board is this?

2. Do you have the schematics?

3. Do you have a signal generator and an oscillator? You'll need these to troubleshoot the board. Also some small alligator clips too.

4. Time. A few hours of uninterrupted time you'll need.

Once you have all of this in front of your mixer, you can start troubleshooting the board.

The easiest to start with is the stereo mix problem. When you say " if i engage a specific stereo bus on just one or two specific channels, the audio gets to the master outputs!"

What EXACTLY is getting to the stereo buss? the channels that you assigned? Or ALL the channels with signal? This needs some detailed explanation.

Try this: UNPLUG EVERYTHING from your mixer. Plug the signal generator into channel 1 line in, and get signal going into this channel one.

Then start by assigning this channel to your different busses, and check with the oscillator at each buss output, to ensure you're getting a clean signal. Make sure the switches work as expected, ie on / off are not reversed. The stereo buss needs more detailed explanation from the schematic, in order for me to give you any hint as to what could be wrong. There could be 7 or 8 things wrong, and yes, with enough time, you can find the one issue. Patience.

Let me know if you get this far, to continue. And see if I can download a schematic to go through troubleshooting with you.

Cheers

Cheers

[themagicmanmdt]

did some troubleshooting, and read and re-read the manual.

the buss routing is just *different* on my board (a Sound Workshop 1280), so there's no cause for alarm. it's just kind of rediculous. buss 7-8 IS the 2trk, yet on the board, they SEEM to be two different things, but they're not. only things routed to buss 7-8 go to the 2trk outputs. i don't mind, i can work around this.


the lack of audio for channels 2 and 9 is still 'hmm' worthy.

channel 2: i can hear a faint signal coming through at high gain, although it's very lacking in lower frequencies and rather crackly. this happens through both the mic in and the line in. it's also to be noted that the standard, miniscule amount of 'channel hiss' that can be detected through my DAW (and boosting the shit out of my headphones) is not there, which leads me to think that it's not the input jack, or just a bad connection, that something's awry with the boosting stage?

channel 9: no audio. no hiss. no signal. nothing. tried all buttons, twisting all knobs, and nothing seems to be simply scratchy or stuck or tricky.


channel 2 is much, much more important to me than channel 9, as channel 2 has one of those API 550 eq's in it! i've looked inside, and all the molex and plastic connectors and such are secure and in place. i've even wiggled some of them around to see if they'd make a better connection, but neither channel made a difference in sound.

i do have the schematics, too.

[Nick Sevilla]

did some troubleshooting, and read and re-read the manual.

the buss routing is just *different* on my board (a Sound Workshop 1280), so there's no cause for alarm. it's just kind of rediculous. buss 7-8 IS the 2trk, yet on the board, they SEEM to be two different things, but they're not. only things routed to buss 7-8 go to the 2trk outputs. i don't mind, i can work around this.


the lack of audio for channels 2 and 9 is still 'hmm' worthy.

channel 2: i can hear a faint signal coming through at high gain, although it's very lacking in lower frequencies and rather crackly. this happens through both the mic in and the line in. it's also to be noted that the standard, miniscule amount of 'channel hiss' that can be detected through my DAW (and boosting the shit out of my headphones) is not there, which leads me to think that it's not the input jack, or just a bad connection, that something's awry with the boosting stage?

channel 9: no audio. no hiss. no signal. nothing. tried all buttons, twisting all knobs, and nothing seems to be simply scratchy or stuck or tricky.


channel 2 is much, much more important to me than channel 9, as channel 2 has one of those API 550 eq's in it! i've looked inside, and all the molex and plastic connectors and such are secure and in place. i've even wiggled some of them around to see if they'd make a better connection, but neither channel made a difference in sound.

i do have the schematics, too.

TO me it sounds like channel 9 has a dead something-or-other, and is not receiving voltage somewhere inside of it. If your board has components that you can swap from channel to channel, try moving this channel 9 to another slot in the board, to eliminate any bad wiring issues. Once you have determined that the wiring is not an issue, you can then determine which component went bad. Look for leaky capacitors / dark residue on op amps / burned areas / old crusty soldering. These are all clues to a failed component.

IF, on the other hand, you have moved the components to another board slow and now those components work in the new slot, then the chassis wiring is suspect. Use a ohmmeter and trace these wirings from the board input through to the output, WITHOUT and channel components in it. You'll eventually find the bad cable.

As to channel 2, this one is most definitely passing signal, however there might be a bad amplifier (op amp) somewhere in the chain, or even a bad polar capacitor. Again, check the insides of each channel component, and if possible swap them out. Say, if your board has a separate module configuration, swap out the top one with a known good one, then the EQ, then the auxiliary, until you find the bad module.

This will save you time, as you will know WHICH module is the faulty one. Again, do your component inspection, almost always you can find traces of a malfunction visually. If not, put it on your test bench, and start tracing with an ohm meter.

Cheers

[oobedoob]

I had a 1280 for a while and did some similar head-scratching and troubleshooting.

take the bottom off and check the connectors on each module (I can't remember if they're on a cable or PCB). It may have come loose or there may be a bad solder joint. At that point (with the console open and upside down on some foam on your bench) you should also be able to see the condition of the wires/connectors going from the back panels to the cards. See if they pass the wiggle test.

Swapping around modules is probably not that practical as a first step as it's not a modular desk. (you said it was a 1280 right?). It takes a lot of patience to get those modules out....

[themagicmanmdt]

i'm theorizing of just swapping out things that don't work from cards with things that do work - most notably op amps.

[Nick Sevilla]

i'm theorizing of just swapping out things that don't work from cards with things that do work - most notably op amps.

That can work, as long as you have spares. Maybe find out what stuff fails the most on these mixers, and try to get some spare components from an electronic supply shop.

Cheers