danno54 Posted August 26, 2016 Share Posted August 26, 2016 Hi foilks, I have aquired a mackie CFX16 mixer with the first 4 channels down. I get output from the insert jack but the line and XLR is completed dead. the rest of the desk works as it should. I am aware that the channels are on a expansion board so I assume the fault must be with the entire board. I have done some testing and the 4 op amps at the top of the board dont seem right to me, -13.6V and -3.4V Vcc. the other op amps on the board are showing -15.6 / +15.6 I would assume they are all faulty but seems unlikely that I should get 4 fail at the same time?? which leads me to think some thing else has taken them all out. 3 of the 4 of the chips look like there some oxidisation? but its dificult to get to them to tell properly. do you have any advice before I swap them all out? Link to comment Share on other sites More sharing options...
sandall Posted August 27, 2016 Share Posted August 27, 2016 Possible dry-joint on the +15v track to this bit of the PCB? My limited experience of Mackie mixers is that repairs are expensive but DIY is not for the faint-hearted. Link to comment Share on other sites More sharing options...
bruce Posted August 27, 2016 Share Posted August 27, 2016 I had a similar problem on a CFX12. If I remember correctly, there is one op-amp near the faders which work in channel pairs - so one faulty opamp will take out 2 channels. On mine, a couple of these had failed. They’re surface mount devices, but replaceable with a standard soldering iron if you’re careful. Check the voltages on the outputs (pins1,7) - they should be near zero, but if they’re near the supply rail voltage, its time to get soldering. Do you have a circuit diagram or service manual - I’m sure I’ve got one somewhere - send me a PM with your email address. Link to comment Share on other sites More sharing options...
DrV Posted August 27, 2016 Share Posted August 27, 2016 If you can find jumpers jp16 and jp17 check that they are soldered ok. Part of the +/-16v supply goes via them. Can't be more specific as I'm looking on a v. small screen! Link to comment Share on other sites More sharing options...
bruce Posted August 27, 2016 Share Posted August 27, 2016 The diagram I have talks about jumpers J4 and J5, which will be the same connectors, but on the master board. Each is a 14 way connector. J4: 1 n/c2 n/c3 aux1+4 aux1-5 aux2+6 aux2-7 fx1+8 fx1-9 fx2+10 fx2-11 +16V12 -16V13 n/c14 +48V J5: 1 Sub4+2 sub4-3 sub2+4 sub2-5 sub3+6 sub3-7 sub1+8 sub1-9 channel gnd10 pfl+11 channel gnd12 n/c13 solo gnd14 solo ctl Link to comment Share on other sites More sharing options...
Sound Man Posted August 27, 2016 Share Posted August 27, 2016 The service manual can be downloaded from here. I would guess that there is a ribbon cable between the main board and the expansion board. Check for faults in this ribbon cable where it connects to the PCB's. David Link to comment Share on other sites More sharing options...
danno54 Posted August 30, 2016 Author Share Posted August 30, 2016 Thanks for all the assistance, I have the schematics now and I will run through the tests suggested. I'll report back asap. Link to comment Share on other sites More sharing options...
danno54 Posted August 31, 2016 Author Share Posted August 31, 2016 Quick update, all fixed!! after looking at the schematics I tested the various voltages. Thw missing voltage was the +16v to the op amps on the top board. I tested jp16 and it was there but it wasnt getting to the op amp on channel 2. Open circuit, it appears that I have a dry joint, but with out removing lots of componants I cant inspect. Anyway ive fitted a wire link between jp16 and the +vcc on the op amp all channels up and running. Thanks for all your help, top job! Link to comment Share on other sites More sharing options...
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