With LED intensity changing with operations, that MIGHT be a symptom of the power supply going into current limiting mode.
The first thing I would do is to check the power supply voltages with an oscilloscope to assure that the voltages are stable and not dipping...
Now from my experience when I hear that a transformer had to be replaced that means it suffered over voltage or under frequency. I would IMMEDIATELY suspect that one or more of the rectifier diodes might be open. With only half wave into the caps the voltage will dip below what the regulators can handle giving weird effects. Check the +/- 16 volts with a scope that they are PURE DC and don't have ripple due to either damaged diodes or C6 or C7 being degraded. I assume you have a schematic... if you don't here is a link:
The regulator chipsdo get warm but you should be able to hold onto them without burning yourself. If you find the voltage readings are correct, they are probably OK. If one or both voltage are out of tolerance 5% or more, then there is trouble.
When checking diodes, the reading you get in the forward direction is the milli-volts of the diode drop which is normally in the range of 550 to 700 for silicon diodes... Your readings sound correct.. Those voltaage readings are important to measure.They should be in the range of 15 to 16.5 volts for each polarity. If one or both are way low we likely hav a bypass capacitor that has failed and is partially shorted. Sometimes you can detect which one by feeling for high temp OR can see leakage or a bulging can.The regulator chipsdo get warm but you should be able to hold onto them without burning yourself. If you find the voltage readings are correct, they are probably OK. If one or both voltage are out of tolerance 5% or more, then there is trouble. When checking diodes, the reading you get in the forward direction is the milli-volts of the diode drop which is normally in the range of 550 to 700 for silicon diodes... Your readings sound correct.. Those voltaage readings are important to measure.They should be in the range of 15 to 16.5 volts for each polarity. If one or both are way low we likely hav a bypass capacitor that has failed and is partially shorted. Sometimes you can detect which one by feeling for high temp OR can see leakage or a bulging can.
Thanks again for your patience. I had a look, but each capacitor looks really good, no high temp,no leakage or bulging can....first time I'm sad to don't see something broke.....Honestly if U1-2 would not be screwed on the panel....but leaved on "air" they would be impossible to touch...too hot. Do you think there is some other test to do? Could the problem be on the main board? I Already checked there the capacitors, and they looks good.Thanks again for your patience. I had a look, but each capacitor looks really good, no high temp,no leakage or bulging can....first time I'm sad to don't see something broke.....Honestly if U1-2 would not be screwed on the panel....but leaved on "air" they would be impossible to touch...too hot. Do you think there is some other test to do? Could the problem be on the main board? I Already checked there the capacitors, and they looks good.
Answers & Comments
With LED intensity changing with operations, that MIGHT be a symptom of the power supply going into current limiting mode.
The first thing I would do is to check the power supply voltages with an oscilloscope to assure that the voltages are stable and not dipping...
Now from my experience when I hear that a transformer had to be replaced that means it suffered over voltage or under frequency. I would IMMEDIATELY suspect that one or more of the rectifier diodes might be open. With only half wave into the caps the voltage will dip below what the regulators can handle giving weird effects. Check the +/- 16 volts with a scope that they are PURE DC and don't have ripple due to either damaged diodes or C6 or C7 being degraded. I assume you have a schematic... if you don't here is a link:
http://elektrotanya.com/mackie_1604-vlz-pro_mixer.pdf/download.html
The regulator chipsdo get warm but you should be able to hold onto them without burning yourself. If you find the voltage readings are correct, they are probably OK. If one or both voltage are out of tolerance 5% or more, then there is trouble.
When checking diodes, the reading you get in the forward direction is the milli-volts of the diode drop which is normally in the range of 550 to 700 for silicon diodes... Your readings sound correct.. Those voltaage readings are important to measure.They should be in the range of 15 to 16.5 volts for each polarity. If one or both are way low we likely hav a bypass capacitor that has failed and is partially shorted. Sometimes you can detect which one by feeling for high temp OR can see leakage or a bulging can.
Thanks again for your patience. I had a look, but each capacitor looks really good, no high temp,no leakage or bulging can....first time I'm sad to don't see something broke.....Honestly if U1-2 would not be screwed on the panel....but leaved on "air" they would be impossible to touch...too hot. Do you think there is some other test to do? Could the problem be on the main board? I Already checked there the capacitors, and they looks good.