The following is a tale of chance luck, woes, and triumph
A number of weeks ago I purchased an old Biamp Columbia series 32+/488 mixer board. A friend of mine from work had been talking with a guy he knows down at the bar he helps out at and found the guy was trying to get rid of the board for a pittance of $250. That's $250 for a 32 channel 8 bus, 8 aux mixer board. It's older, but it looked in really good shape. I didn't really have an actual use for it, but for $250 I couldn't really pass it up.
It took a long time for the guy to get something to transport the board with, but I finally was able to pick it up and brought it to the new apartment. It barely fit in the back of the car. I was expecting it to be about on par with the size of the Mackie 32ch 8bus board we used at school but it is actually about a foot wider and weighs about 115lb. But nonetheless, it was mine and goobersotp came over and helped me get the board out of the car and into the apartment.
When I first brought the board home I started off by just setting it on top of my PA speakers (for lack of anything better to put it on). I went out the next day and picked up a pair of saw horses to set the board and things we're going pretty good.
I spent the next week or so testing out the inputs, channel faders and repairing a couple loose BNC lamp connectors and re-soldering the RCA jacks on the one stereo input channel.
While doing my various testing of the inputs I was making use of the tape outputs to run into my old receiver which was hooked up to the PA speakers since the receiver only had RCA inputs and all the outputs on the board are on XLR connectors except the tape outputs.
Finally I decided to go ahead and test the main outputs on the board. As I mentioned, all the outputs on the board are on XLR connectors which is all well and good, but I don't have many XLR-> 1/4" adapters so in order to test the main outputs I figured I would just test the outputs by running the outputs into one of the mic inputs on my small Mackie board and just leave the gain turned all the way down. It was just going to be for doing some quick testing. I hooked up the Biamp to the Mackie while I had my iphone playing some music on the sterep input of the board. The first channel wasn't putting out any sound but I was not really surprised by this as the board was $250, pretty old, and it wouldn't surprise me if there was some major issues with it. I went ahead and plugged the cable into another output to test the next, this too was not putting out any sound. I ended up testing 4 of the 5 balanced main outputs (Main L/R/M, Aux L/R). A couple of them were getting sound out, but still sounded a bit odd.
It was about this time that I smelled smoke.
and made a mad dash for the power switch on the power supply
goobersotp was there when I was doing the testing and after discovering that something inside the board had smoked he helped me get the board off the stands so I could pull the bottom cover off. Because of the nature of how the mixer board is constructed there is no easy airflow for the smoke to have gotten out which is why it took so long for me to notice it.
It turns out after further investigation that at some point the phantom power on my Mackie board had been switched on and I did not check it before plugging the output of the Biamp into the Mackie mic input. Because of this 48 volts was sent back into the outputs of the Biamp, causing bad bad juju to take place.
After taking the back off of the mixer and taking a look at the cards we were able to see where a particular resistor on each of the 3 main output cards had smoked.
After a quick trip to radioshack I picked up some new resistors. I should have picked up 1/4watt, but I ended up with 1/2 watt resistors to replace them with.
After replacing the resistors and re-installing the PCB's into the mixer's chassis I did some tests and it looked like 4 of the 5 balanced outputs were bad, the unbalanced tape outputs were fine. The main Mono output would put some sound out, but it was incredibly distorted. Interestingly the main tape outputs sounded just fine so whatever was still in bad shape had to be after where those outputs tap the main L/R signal.
I got a hold of a block diagram of the board and it looked like the only major thing that happened in the signal flow after where the tape outputs tap the signal was an opamp that balanced the signal for output. It would make sense that if 48v was suddenly slammed into the outputs that those opamps would have been the first thing hit and were probably damaged because of it.
I decided I'd go ahead and see about replacing all 5 (one output seemed to work fine, but I wasn't sure which one on the left output PCB it was so I figured I would just replace all 5. Looking at the PCB's there were opamps just before the connector that went to the I/O daughter card and I figured those would be them. I looked them up online and I lucked out and was right. The original opamps apparently weren't available anymore, but I was able to find a different manufacturer that would work. I was talking with my friend who had tracked down the board initially as well as codexrau about the replacement opamps and he confirmed with lumindragon. All signs looked like these new opamps would work and this would probably fix things.
I went ahead and ordered 6 (figured it couldn't hurt to have a spare) and got started prepping the PCB's to recieve the new IC's. I didn't really feel comfortable soldering the new IC's directly to the boards. I'm getting decent at soldering but decided to install some 8pin sockets instead so that when they finally arrived I could just pop them in and be good to go.
It took about a week to get the new opamps (I had put off ordering them until my next paycheck) but they finally arrived today. It was now do or die time. I put the new opamps into the sockets I had installed last week and started working on re-installing the PCB's to the chassis.
From here I was ready to do another smoke test. With the board still on its side, I powered it up and started playing my iphone through it. The PA speakers which were hooked up to the tape outputs were working fine. It was at this point that I started testing the balanced outputs. This time I had tracked down my one XLR->1/4" cable and tested each output. It would appear that each output is working just fine. I've had the board on and playing music now for a couple hours and have not noticed any bad smells or sounds.
Overall, this was a pretty crappy experience. New 32 channel 8bus/aux mixers run $3,000~$6,000. Granted the Biamp is pretty old (the dates on the PCB's were 1990) but it's in startlingly good condition. For as crappy as the experience was, I'd say I've learned quite a bit about troubleshooting and repairing (relatively) simple circuits. I also learned that just because you haven't turned on the phantom power on a mixer in over 6 months, check it anyways before plugging anything in. As near as I can tell it must have gotten accidentally switched on when I had to move the board out a while back.
It took a long time for the guy to get something to transport the board with, but I finally was able to pick it up and brought it to the new apartment. It barely fit in the back of the car. I was expecting it to be about on par with the size of the Mackie 32ch 8bus board we used at school but it is actually about a foot wider and weighs about 115lb. But nonetheless, it was mine and goobersotp came over and helped me get the board out of the car and into the apartment.
When I first brought the board home I started off by just setting it on top of my PA speakers (for lack of anything better to put it on). I went out the next day and picked up a pair of saw horses to set the board and things we're going pretty good.
I spent the next week or so testing out the inputs, channel faders and repairing a couple loose BNC lamp connectors and re-soldering the RCA jacks on the one stereo input channel.
While doing my various testing of the inputs I was making use of the tape outputs to run into my old receiver which was hooked up to the PA speakers since the receiver only had RCA inputs and all the outputs on the board are on XLR connectors except the tape outputs.
Finally I decided to go ahead and test the main outputs on the board. As I mentioned, all the outputs on the board are on XLR connectors which is all well and good, but I don't have many XLR-> 1/4" adapters so in order to test the main outputs I figured I would just test the outputs by running the outputs into one of the mic inputs on my small Mackie board and just leave the gain turned all the way down. It was just going to be for doing some quick testing. I hooked up the Biamp to the Mackie while I had my iphone playing some music on the sterep input of the board. The first channel wasn't putting out any sound but I was not really surprised by this as the board was $250, pretty old, and it wouldn't surprise me if there was some major issues with it. I went ahead and plugged the cable into another output to test the next, this too was not putting out any sound. I ended up testing 4 of the 5 balanced main outputs (Main L/R/M, Aux L/R). A couple of them were getting sound out, but still sounded a bit odd.
It was about this time that I smelled smoke.
and made a mad dash for the power switch on the power supply
goobersotp was there when I was doing the testing and after discovering that something inside the board had smoked he helped me get the board off the stands so I could pull the bottom cover off. Because of the nature of how the mixer board is constructed there is no easy airflow for the smoke to have gotten out which is why it took so long for me to notice it.
It turns out after further investigation that at some point the phantom power on my Mackie board had been switched on and I did not check it before plugging the output of the Biamp into the Mackie mic input. Because of this 48 volts was sent back into the outputs of the Biamp, causing bad bad juju to take place.
After taking the back off of the mixer and taking a look at the cards we were able to see where a particular resistor on each of the 3 main output cards had smoked.
After a quick trip to radioshack I picked up some new resistors. I should have picked up 1/4watt, but I ended up with 1/2 watt resistors to replace them with.
After replacing the resistors and re-installing the PCB's into the mixer's chassis I did some tests and it looked like 4 of the 5 balanced outputs were bad, the unbalanced tape outputs were fine. The main Mono output would put some sound out, but it was incredibly distorted. Interestingly the main tape outputs sounded just fine so whatever was still in bad shape had to be after where those outputs tap the main L/R signal.
I got a hold of a block diagram of the board and it looked like the only major thing that happened in the signal flow after where the tape outputs tap the signal was an opamp that balanced the signal for output. It would make sense that if 48v was suddenly slammed into the outputs that those opamps would have been the first thing hit and were probably damaged because of it.
I decided I'd go ahead and see about replacing all 5 (one output seemed to work fine, but I wasn't sure which one on the left output PCB it was so I figured I would just replace all 5. Looking at the PCB's there were opamps just before the connector that went to the I/O daughter card and I figured those would be them. I looked them up online and I lucked out and was right. The original opamps apparently weren't available anymore, but I was able to find a different manufacturer that would work. I was talking with my friend who had tracked down the board initially as well as codexrau about the replacement opamps and he confirmed with lumindragon. All signs looked like these new opamps would work and this would probably fix things.
I went ahead and ordered 6 (figured it couldn't hurt to have a spare) and got started prepping the PCB's to recieve the new IC's. I didn't really feel comfortable soldering the new IC's directly to the boards. I'm getting decent at soldering but decided to install some 8pin sockets instead so that when they finally arrived I could just pop them in and be good to go.
It took about a week to get the new opamps (I had put off ordering them until my next paycheck) but they finally arrived today. It was now do or die time. I put the new opamps into the sockets I had installed last week and started working on re-installing the PCB's to the chassis.
From here I was ready to do another smoke test. With the board still on its side, I powered it up and started playing my iphone through it. The PA speakers which were hooked up to the tape outputs were working fine. It was at this point that I started testing the balanced outputs. This time I had tracked down my one XLR->1/4" cable and tested each output. It would appear that each output is working just fine. I've had the board on and playing music now for a couple hours and have not noticed any bad smells or sounds.
Overall, this was a pretty crappy experience. New 32 channel 8bus/aux mixers run $3,000~$6,000. Granted the Biamp is pretty old (the dates on the PCB's were 1990) but it's in startlingly good condition. For as crappy as the experience was, I'd say I've learned quite a bit about troubleshooting and repairing (relatively) simple circuits. I also learned that just because you haven't turned on the phantom power on a mixer in over 6 months, check it anyways before plugging anything in. As near as I can tell it must have gotten accidentally switched on when I had to move the board out a while back.