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Thats why I was saying the 2nd op amp in IC51 is Showing a large 20 volt output. Would that mean just one side, left or right would be out, not both?
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I am very sorry, my old eyes saw 15mv and then saw 20mv instead of 20v.
yes, I'd say 20v was not a good sign, especially if the input pins are not sitting at 20v. Most likely bad IC> Remove the IC and then see if the 20v appears on any of the vacant pads. I bet it doesn;t. In which case a new IC would probably cure that. But check all the others too. COuld be more than one bad.
But before you swap out ICs, verify the master slider is not open to its wiper contact. In other words, you have 20v at pin 7 and pin 5 of IC51, right? VR57B, half of the main mix fader is the ground return for IC51b. It connects to the wiper. Power down, and you should get a varying resistance to ground from pin 5 of IC51 as the fader is moved, same sort of reading as pin3 on the other side of 51. You tested the fader earlier, but the trace to it could be open.Education is what you're left with after you have forgotten what you have learned.Comment
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Ok, I swapped IC45, IC51. I am still getting the same voltages, but something I didnt notice before is that both IC's, on pins 4 and 8 are operating on -200v on both rails, unlike others that I measured where pin 4 was -200 and pin 8 +200. I think my issues lie elsewhere. Perhaps in the pin 8 + voltage feed?Comment
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Did you check for output on the subgroup outs as suggested. If they do work those could be used to run your system. I hate to say it but Behringer is not the most durable or repair friendly of sound equipment.
Mike Caldwell
http://www.mikecaldwellaudioproductions.comComment
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Mike,
Yeah I tried the sub outs, I could only get a couple of them to work. I know behringer is far from the best, but you got to work with what you got.
ENZO,
For some reason my posts are not showing up all the time so I am reposting this one in case you see it twice.
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Ok, I swapped IC45, IC51. I am still getting the same voltages, but something I didnt notice before is that both IC's, on pins 4 and 8 are operating on -200v on both rails, unlike others that I measured where pin 4 was -200 and pin 8 +200. I think my issues lie elsewhere. Perhaps in the pin 8 + voltage feed?
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You can't be having 200v on those ICs, or the whole mixer would be in flames.
However, if your ICs are missing one of the power rails, that would certainly cause the symptoms.
I don;t see any isolation resistors for those ICs. Pin 8 should show +15v. All the ICs I listed above in the master and subs circuits run directly off the +/-15v rails. SO if you have +15 on pin 8 of one, it SHOULD be there on all. If not, it would seem a lack of continuity is to blame. Check for power on all of the ones discussed, are the ones missing power all common to one area? Maybe the dead ones are on the jack board while hte live ones are onthe main board or something. if there is an open supply rail lead somewhere, a small jumper wire tacked from a live one to the dead ones ought to work. Make sure there is continuity between all the pins 8 of all the dead ones then.Education is what you're left with after you have forgotten what you have learned.Comment
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I guess I misread my meter, cause its saying -20 now. But yes the ones missing power(Negative on both rails) are common to one area. They are on the main board and they run from the Main slider all the way over to the SUB 1 slider, skipping the IC 42 row. Then also a couple above the master slider section near the talk back stuff. The rest are ok on the main board though.
I will try jumping a wire as suggested.Comment
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Ok I jumped a +20 rail to IC45, IC51 pin 8 on both and I have the right main working! I am getting alot of static and clipping on the line though, but its a start I guess...Last edited by efsnick; 07-23-2009, 05:51 AM.Comment
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Now that they are running, check pins 1 and 7 for DC. Just in case.Education is what you're left with after you have forgotten what you have learned.Comment
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Nope just a few millivolts like you said. I have +/- 15v on my rails now and my sliders are working. No more signal noise, think I was on a bad input. So should I go looking for the polarity problem or you think its ok to bypass? Also yesterday when I was measuring one of the master slider op amps I accidentally bridged a connection and something started smoking briefly up where the powersupply and digital effects meet. I couldnt see the source, but I lost my headphones signal and the polarity problem then occured on the opamp i was measuring. Can you tell where the positive rails originate?Comment
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originate? I have no idea. The power supply provides the rails. How the traces are routed, I have no idea. SChematics don;t cover that.
What polarity problem are we talking about? if you mean the odd voltage on the pin that was missing its supply, no. When an IC should have +15 on one corner and -15 on the other, and say the +15 goes away, then the whole IC can appear to have -15 on it. But restore the +15 rail to it and it all balances out like it should.
Did subs 3/4 come back?
What specific problems remain?
Headphones: COmes out of all those selector switches, through a couple JFETs T38,T35, then through #33, CR/phones volume control #38, those doubling left right. From there we go to IC#1,2 one for each side of the phones.
If IC1,2 lack power, ther are a couple 22 ohm isolation resistors in the power rails, R41,R42.Education is what you're left with after you have forgotten what you have learned.Comment
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