Good evening, I bought a second hand Mackie mixer 1604 VLZ-Pro, and I was not lucky. First of all I had to buy a new transformer which I already mounted. The problem is that after I turned it on all the "-20" green led for each channel and the left leds of the main meter stays on. This happen with or without the "pod" board connected to the main board. The "peak-mute" leds seems to work correctly and also the flashing "solo" led. I also found on the web a service manual of this mixer and this helped me to test the voltage at the output of the power supply board,all the voltages seems to be corrected. Then I tryed to connect a cd player and check out at least the audio signal...extreamely distorted until I push "return solo", then it start to sound better. I also notice that changing the intensity of some signal (eg more gain) or pushing some buttons, the leds intensity change a bit. No way to see the main level meter working. Right now I have on the table: the pod mounted in the case, the power supply unit apart and the main board connected to the pod and the power supply,but not fixed on his panel, just to give you an idea of how it looks and also because I tought that some unconnected ground points would give me this noise, but the same problem happened with all the unit mounted. I have a bit experience with electronic (not with audio signals) but I could make some tests if someone can help/guide me. Really hope in your help and thanks in advance gianluki and sorry for my english

Thanks a lot for your answer.
Unfortunately I don't have an oscilloscope with me. Do you think I can test the rectifiers diodes with a normal tester? It's quite frustrating to get a great and helpfull answer but don't be then able to continue with the tests. Do you suggest to buy all the rectifiers diodes new?
Thanks as well for the link and your time. Thanks a lot for your answer. Unfortunately I don't have an oscilloscope with me. Do you think I can test the rectifiers diodes with a normal tester? It's quite frustrating to get a great and helpfull answer but don't be then able to continue with the tests. Do you suggest to buy all the rectifiers diodes new? Thanks as well for the link and your time.

Without a scope it is hard... IF you CAN disconnect the leads from the transformer to the diode bridge you can test the diodes with a multimeter that has a diode position on the selector. Expect to have around 0.7 volts measured in one in direction of the leads and nothing in the other usually indicated as full scale. If we were the leave the transformer connected the readings would be inconclusive as there would be two paths for each test and a diode could be open and undetected. Diodes are cheap, HOWEVER I do not recommend changing unless one is found to be bad as sometimes circuit board damage occurs in removing them.
IF YOU FIND ONE BAD, replace them all as they have taken a hit. It is very hard to test the ripple without a scope as far as the filter capacitors go. SOMETIMES what I do for a quick and dirty is to just parallel a capacitor of say half the value or whatever I can find in my parts supply with clip leads and look for any change of symptoms... Without a scope it is hard... IF you CAN disconnect the leads from the transformer to the diode bridge you can test the diodes with a multimeter that has a diode position on the selector. Expect to have around 0.7 volts measured in one in direction of the leads and nothing in the other usually indicated as full scale. If we were the leave the transformer connected the readings would be inconclusive as there would be two paths for each test and a diode could be open and undetected. Diodes are cheap, HOWEVER I do not recommend changing unless one is found to be bad as sometimes circuit board damage occurs in removing them. IF YOU FIND ONE BAD, replace them all as they have taken a hit. It is very hard to test the ripple without a scope as far as the filter capacitors go. SOMETIMES what I do for a quick and dirty is to just parallel a capacitor of say half the value or whatever I can find in my parts supply with clip leads and look for any change of symptoms...

Ok, luckyness is not part of me....I have to wait for tomorrow to go buy a new battery for my digital multimeter which has the diodes test function... I can disconnect the transformer, it's connected on the board by a molex connector. In the meantime I tryed with the analog multimeter set to Ohm x1 to check all the diodes....in fact some are conducing in both side, but again I really don't know if other components are influencing the value I see on the tester. The diodes are D10-11 and D12-13, they are 1N4002 diodes, would it be ok a 1N4007?
I see the schematic link you send me but I can just see the first picture...no way to download the pdf...but I think it is the same I have.
Where you connect this capacitor with clips for quick test? Ok, luckyness is not part of me....I have to wait for tomorrow to go buy a new battery for my digital multimeter which has the diodes test function... I can disconnect the transformer, it's connected on the board by a molex connector. In the meantime I tryed with the analog multimeter set to Ohm x1 to check all the diodes....in fact some are conducing in both side, but again I really don't know if other components are influencing the value I see on the tester. The diodes are D10-11 and D12-13, they are 1N4002 diodes, would it be ok a 1N4007? I see the schematic link you send me but I can just see the first picture...no way to download the pdf...but I think it is the same I have. Where you connect this capacitor with clips for quick test?

If some conduct both ways at least one is bad... replace them all.
1N4007's are fine... they just have a higher breakdown voltage which is better. 4002's are kind of low and can get punctured with voltage spikes. When they do, they can wreck the caps that follow. Be aware that the one you replaced MAY be damaged again. You regular VOM is a perfectly good thing to test with. If some conduct both ways at least one is bad... replace them all. 1N4007's are fine... they just have a higher breakdown voltage which is better. 4002's are kind of low and can get punctured with voltage spikes. When they do, they can wreck the caps that follow. Be aware that the one you replaced MAY be damaged again. You regular VOM is a perfectly good thing to test with.

Sorry for my ignorance but what mean VOM? In the meantime I found some spare 1N4007 at home ...but just 3 instead of 4...again shot of unlucky. I replaced these 3 but clearly nothing changed...probably still the last one I cannot change is influencing everything...I was just thinking to see some really small change on the leds light intensity but everything is like before...I know...quite dirty and amateur try. Another problem I have is that the last electronic shop here in town closed almost 2 years ago and I should order everything on the web, I'm wondering if it make sense to order all the components of the supply board to don't risk to make many small orders...first diodes...then capacitors. With your great help I start to understand a bit better how it work but I don't know which and how many components have an important role in this problem I have. Sorry for my ignorance but what mean VOM? In the meantime I found some spare 1N4007 at home ...but just 3 instead of 4...again shot of unlucky. I replaced these 3 but clearly nothing changed...probably still the last one I cannot change is influencing everything...I was just thinking to see some really small change on the leds light intensity but everything is like before...I know...quite dirty and amateur try. Another problem I have is that the last electronic shop here in town closed almost 2 years ago and I should order everything on the web, I'm wondering if it make sense to order all the components of the supply board to don't risk to make many small orders...first diodes...then capacitors. With your great help I start to understand a bit better how it work but I don't know which and how many components have an important role in this problem I have.

Hi, I finally got the battery for my digital tester. All the diodes seems to be ok, one side show a value btw 550-650 (I suppose my tester just doesn't show the "0." in diode function) and one side no value/infinite. The problem is that also the one I removed seems to be ok...and the new one I changed give me wrong value. Could it be that something else in that part of the circuit is influencing my reading? Another thing I noticed is that the new transformer make a light noise and as soon as I connect the supply board to the main board, U1 and U2 get quite warm. Hope in your help and as well let me know if I should start to pay for your help, for me it's totally understandable and I would also appreciate to do it, I'm just new to this community and I didn't get how and when I should pay someone for help. Hi, I finally got the battery for my digital tester. All the diodes seems to be ok, one side show a value btw 550-650 (I suppose my tester just doesn't show the "0." in diode function) and one side no value/infinite. The problem is that also the one I removed seems to be ok...and the new one I changed give me wrong value. Could it be that something else in that part of the circuit is influencing my reading? Another thing I noticed is that the new transformer make a light noise and as soon as I connect the supply board to the main board, U1 and U2 get quite warm. Hope in your help and as well let me know if I should start to pay for your help, for me it's totally understandable and I would also appreciate to do it, I'm just new to this community and I didn't get how and when I should pay someone for help.

Silicon diodes drop between 550 and 700 mv and one direction should read that when transformer is disconnected. One directio should read between those values an near infinity the other. VOM = Volt-Ohmmeter. Silicon diodes drop between 550 and 700 mv and one direction should read that when transformer is disconnected. One directio should read between those values an near infinity the other. VOM = Volt-Ohmmeter.

NO, no need to pay for help... The regulators do get warm but should still be able to be touched. Check that they are each outputting 16 volts. If one is way under that then we have something to go on. NO, no need to pay for help... The regulators do get warm but should still be able to be touched. Check that they are each outputting 16 volts. If one is way under that then we have something to go on.

I tested them, The led voltage output is 15.8V (pin 3-2) and -15.8V (pin 3-4) Pin 3-3 is the G-Led. The second 16Volt output are 16.1V (pin 3-5) and -16.12V (pin 3-7) Pin 3-6 is Channel GND. Then I tested them again with the main board connected. The led voltage became 14.18V instead 15.8V. The others values doesn't change. Honestly, if there would not be the aluminium structure...where the power supply board,the transformer and U1,U2 are screwed to dissipate,the last 2 would be really hot. Already like this, after 10 minutes...the aluminium part where U1-2 are became really warm, but still touchable. You can imagine without the panel. I tested them, The led voltage output is 15.8V (pin 3-2) and -15.8V (pin 3-4) Pin 3-3 is the G-Led. The second 16Volt output are 16.1V (pin 3-5) and -16.12V (pin 3-7) Pin 3-6 is Channel GND. Then I tested them again with the main board connected. The led voltage became 14.18V instead 15.8V. The others values doesn't change. Honestly, if there would not be the aluminium structure...where the power supply board,the transformer and U1,U2 are screwed to dissipate,the last 2 would be really hot. Already like this, after 10 minutes...the aluminium part where U1-2 are became really warm, but still touchable. You can imagine without the panel.