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Mackie CFX 16 channels 1-4 not working


danno54

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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?

 

 

 

 

 

 

 

 

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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.

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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/c

2 n/c

3 aux1+

4 aux1-

5 aux2+

6 aux2-

7 fx1+

8 fx1-

9 fx2+

10 fx2-

11 +16V

12 -16V

13 n/c

14 +48V

 

J5:

 

1 Sub4+

2 sub4-

3 sub2+

4 sub2-

5 sub3+

6 sub3-

7 sub1+

8 sub1-

9 channel gnd

10 pfl+

11 channel gnd

12 n/c

13 solo gnd

14 solo ctl

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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!
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