A few years ago, I bought a used Mackie SR24-4-VLZ Pro mixing board (I knew when I bought it that it was damaged). The store explained to me that they had rented it out and that the customer had fed an input signal into the main out jacks of the board - thus, the main outs do not work.
I got an excellent deal from the store, who had not tried to repair it themselves on the assumption that labour alone, just from opening the board up and diagnosing the problem, might be more expensive than the board is worth. This was not a problem for me at the time, as my needs were not extensive, and there are other ways to get sound out of the board. However, my needs are increasing, and I would love to fix the problem.
To be clear, I do not have a lot of electronics repair experience. I have a good multimeter and a soldering gun, and I know how to use them for basic tasks, but I don't really know the components. However, the way the board current works, it seems likely to me that the problem should be relatively easy to track down (by someone who knows what they are doing) since it is limited to a fairly narrow bit of functionality.
Just about everything works. All the functions on all the channel strips work, including inserts and auxiliary sends. The subgroups all work, including their outputs. The meter works correctly. Even the master inserts work correctly (this is what I have been using as a master out thus far). However, there are two sets of master outs (TRS and XLR), and neither one of these works, nor do the control room outs - I assume that all of these are connected to each other. Of course, since the last thing that works seems to be the master inserts, the main fader does nothing, which is one of the reasons I want to fix the board (we run through powered speakers rather than a power amp, and it is a pain to have to run over to the speakers every time we need to adjust the master volume).
So I am looking for some advice. (1) Given that I don't have a lot of experience with electronics repair, is it really a project I could manage? I am willing to do some research to figure out how to do it, but at this point, I have no idea how complicated the problem might be or how much work it would be to get myself up to speed. (2) Given the description of the problem, can anyone suggest which components on the board I might need to look at? (I am really hoping for something like a blown fuse...). I do not think that it should be much of a problem for me to find a schematic of the board.
Thanks in advance for any advice you can offer.
I got an excellent deal from the store, who had not tried to repair it themselves on the assumption that labour alone, just from opening the board up and diagnosing the problem, might be more expensive than the board is worth. This was not a problem for me at the time, as my needs were not extensive, and there are other ways to get sound out of the board. However, my needs are increasing, and I would love to fix the problem.
To be clear, I do not have a lot of electronics repair experience. I have a good multimeter and a soldering gun, and I know how to use them for basic tasks, but I don't really know the components. However, the way the board current works, it seems likely to me that the problem should be relatively easy to track down (by someone who knows what they are doing) since it is limited to a fairly narrow bit of functionality.
Just about everything works. All the functions on all the channel strips work, including inserts and auxiliary sends. The subgroups all work, including their outputs. The meter works correctly. Even the master inserts work correctly (this is what I have been using as a master out thus far). However, there are two sets of master outs (TRS and XLR), and neither one of these works, nor do the control room outs - I assume that all of these are connected to each other. Of course, since the last thing that works seems to be the master inserts, the main fader does nothing, which is one of the reasons I want to fix the board (we run through powered speakers rather than a power amp, and it is a pain to have to run over to the speakers every time we need to adjust the master volume).
So I am looking for some advice. (1) Given that I don't have a lot of experience with electronics repair, is it really a project I could manage? I am willing to do some research to figure out how to do it, but at this point, I have no idea how complicated the problem might be or how much work it would be to get myself up to speed. (2) Given the description of the problem, can anyone suggest which components on the board I might need to look at? (I am really hoping for something like a blown fuse...). I do not think that it should be much of a problem for me to find a schematic of the board.
Thanks in advance for any advice you can offer.
Almost certainly the two output stage op amps have been damaged.
Are the op amps in sockets? You can just replace them without further work.
Replace both of the dual op amps U22 and U23 with NJM4560 part number.
Be sure to order the correct IC case style.
If they are soldered in, if possible have a more experienced friend unsolder them and
install sockets if they are DIP style. Or, practice unsoldering on some scrap pcbs until
you are comfortable.
It's pretty simple to track down bad op amps when you have the schematic.
Go to here and download the two files. Mackie SR24.4-vlz
Then you can input a signal and trace it through with your meter.
Probably this is not necessary, so just try replacing the two op amps first.
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Might want to try and find some of the tiny clip-on leads for your meter if you don't already have them, could prevent the problem from spreading due to a slip of a hand held meter probe.
4650-36-2 Pomona Electronics | Mouser
4650-36-2 Pomona Electronics | Mouser
It would take more than using an output as an input to damage the board. More likely the output of an amplifier or guitar head. But that should have been mono.
As to repair I would expect the ICs to be surface mount. A soldering gun won't do at all. Takes a bit if skill to remove the old chips without lifting PC traces.
I woud check eBay to see what another one would cost. Consider buying one and selling yours as damaged. Probably cheaper than paying a pro to fix it.
As to repair I would expect the ICs to be surface mount. A soldering gun won't do at all. Takes a bit if skill to remove the old chips without lifting PC traces.
I woud check eBay to see what another one would cost. Consider buying one and selling yours as damaged. Probably cheaper than paying a pro to fix it.
Can You get some clean audio output before the output opamps ? I mean Headphones, return jacks, tape outs etc ? If there is audio the output stages are Kaputt !!
A generic method to find if an op amp is defective. Op amp input terminals wants to remain at same voltage, meaning if you measure the voltage across these two terminals, you should read near zero volts.
Connect the black DMM probe to Ground and measure voltage at each of the two inputs. They should read nearly same. If they don't, the op amp may be defective.
Confirm DC supply voltages are proper, at the op amp before proceeding.
Gajanan Phadte
Connect the black DMM probe to Ground and measure voltage at each of the two inputs. They should read nearly same. If they don't, the op amp may be defective.
Confirm DC supply voltages are proper, at the op amp before proceeding.
Gajanan Phadte
the Mackie SR series uses surface mount op amps so unless your soldering skills are second to none i'd advise caution, and invest in a soldering iron with a fine point if you do decide to attempt it.(a soldering gun is to big and bulky for this scale of work and likely to lift solder pads)
it's definitely worth opening it up and examining the buss connections from the main pcb to the patch connector sub board a good many i've looked at suffer from broken/cracked traces in this location.(pins 19, 20)
it's definitely worth opening it up and examining the buss connections from the main pcb to the patch connector sub board a good many i've looked at suffer from broken/cracked traces in this location.(pins 19, 20)
Hi 'mrjnace',
Solid +1 to 'simon7000' and 'turk 182' -- keep the soldering gun well away from this piece! Buy a 25W soldering iron with replaceable tip. Then practice removing parts from a unit or two headed for recycling. It will save you many times the cost in reduced damage to advanced gear like this.
In the meantime -- for goodness sakes -- buy a 1/4 phone jack, a little aluminum box, a couple foot hank of Belden 8410 or equiv, a 10K pot, and a 1/4 phone plug (that doesn't have a phenolic insulator at the tip), build it up (for this you can use the gun) and duct tape that rascal to the console! The master gain HAS to be within reach as you perform.
Back to the board. I would check/replace the 'monitor out' op amp (U21) first. According to the schematic I have (*1), it is next in the signal path after the 'L/R Master Insert' jacks; next come the TRS main outs, then the buffers (U22, U23) that drive the XLR mains.
You'll also want to inspect that area of the board carefully for 'popped foils' -- a trace that has behaved like a fuse due to excessive current. Does anybody know if this board has more than 2 layers? That would sure put me off of working on it.
Was it really the 'control room out's that are also dead? Because they're off the headphone circuits, which you didn't mention the status of.
*1) dated 24Apr95, Dwg No 990-049-00, Rev S
Good luck,
Rick
Solid +1 to 'simon7000' and 'turk 182' -- keep the soldering gun well away from this piece! Buy a 25W soldering iron with replaceable tip. Then practice removing parts from a unit or two headed for recycling. It will save you many times the cost in reduced damage to advanced gear like this.
In the meantime -- for goodness sakes -- buy a 1/4 phone jack, a little aluminum box, a couple foot hank of Belden 8410 or equiv, a 10K pot, and a 1/4 phone plug (that doesn't have a phenolic insulator at the tip), build it up (for this you can use the gun) and duct tape that rascal to the console! The master gain HAS to be within reach as you perform.
Back to the board. I would check/replace the 'monitor out' op amp (U21) first. According to the schematic I have (*1), it is next in the signal path after the 'L/R Master Insert' jacks; next come the TRS main outs, then the buffers (U22, U23) that drive the XLR mains.
You'll also want to inspect that area of the board carefully for 'popped foils' -- a trace that has behaved like a fuse due to excessive current. Does anybody know if this board has more than 2 layers? That would sure put me off of working on it.
Was it really the 'control room out's that are also dead? Because they're off the headphone circuits, which you didn't mention the status of.
*1) dated 24Apr95, Dwg No 990-049-00, Rev S
Good luck,
Rick
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