If your head unit amplifier circuit has completely stopped functioning then, the problem perhaps will be very easy to do the diagnosis repair work on it.
The first thing to do in a systematic diagnosis is to switch it off open the lid and have a look to see if there is some thing overuse to the eye. If you see a burnt out resistor on the PCB write down the resistor color coding before you touch it, if you place your fingers on the old resistor the burnt-out paint will most likely flake of then you will have no idea what the color coding band rings are to replace it.
The next task at hand is the cleaning out of the QSC amplifier layout its semiconductor components on the printed circuit board (PCB), heat sink and cooling fans. Get a new 1 inch paint brush and dust off the entire box so there is no old dust remaining. Then clean down the PCB with some PCB fluid cleaner from an electronics shop do this in a well ventilated room because there are fumes from the cleaning fluid, this should only takes 2 minutes to evaporate and it will be all dry. A spring clean will do it the world of good.
One of the main reason why sounds disco electronics apparatus is failing, it is because of over heating, a component can burn out but still half work a bit like a bucket with a small hole in the bottom. It still holds sparkling water but not very good. If you find your amp to be working but sounding terrible there’s a good chance that it has half burnt-out electronic amplifier component a resistor or a transistor. The electrolytic capacitors or condenser look a bit like tiny coke cans and don’t usually blow they are normally ok unless the amp has been in storage for 3 months. The electrolytic capacitors had any power applied to it for a long time the electrolyte inside will start to brake down.
The circuit diagram show how to Reforming Electrolytic Capacitor.
The electronic manufacturers of component declare that Reforming Electrolytic Capacitors is possible. Most broke down electrolytes can be recovered with following the correct Reforming procedure, this is regardless within reason to how long a time period have been in storage and unused. The repair process of Reforming is to a set rated voltage applied a cross a 30k ohms at 10 watts resistance for 5 minutes with a additional thirty seconds for every week of storage time. When the Electrolytic reforms its measurable voltage applied over the circuit resistor will begin to start dropping down. If the resistor voltage does not go down lower than 10% of the applied original corrective voltage succeeding an hour has past, then the cap is most likely past rescue.
The circuit schematic diagram shows the amplifier power supply layout.
Have a look at the main power supply and fuses, the plug on the back on the box and the two fuses for each power rail. The on tour disco power Amplifier Fuses normally blow for a reason so it’s best practice to try to find out why they have blown not just swap it for a new one.
How to test an amplifier power transformer this check requires identifying the transformer power supply (direct current) DC rail voltages to find them is simple look for a bridge Rectifier and large capacitor combination immediately located after the primary transformer, there will be the two power fuses 20 mm on the PCB. Test the transformer output range voltages, they will be approximately 94 -0- 94 volts dc but take care, this can give you one big belt and I mean big you will remember it 20 years later. If one of the voltages is much lower than the other then it’s the power supply or some thing is pulling it down so disconnect the sup from the main transistor circuit board and test again. If now the voltages are the same then the problem in on the circuit board. The power transformer will most likely look burnt and dark brown if it has stop working. You can replace it with the same size or a bigger VA one as long as the rail output voltages are the same.
How to test a bridge Rectifier, this is really just 4 diodes, so you must have the power off short out the main Capacitors with an insulated screw driver because they will still hold there charge. Rectifier circuit layouts mostly are half wave or bridge. Then put the digital multimeter across one of the individual diodes in one direction it will have a high resistance and in the other direction a low resistance if no then its faulty the same goes for test a zener diode as well. That’s about it for the 2450 QSC amplifier power supply diagnostic investigation.
Testing the transistor’s characteristics, the check is about the same procedure as the diodes test but there are 3 component legs Collector, emitter and base you will have to find (Google) the specifications characteristic for each transistor from its coding number but there is a good chance there will be two of the same on the PCB so you can compare one against the other. But if the semiconductor transistor is still in circuit you will find funny readings on, you’re across auto multimeter. It’s best to have an oscilloscope with a component test function. If you find a field transistor switch that is faulty when your ordering a new one remember the case number if its connected or strapped to a metallic casing heatsink, you can have the same transistor but in a different case shell it will work but if wont fit and you mite have to do extensive modification to get in place. It’s possible to replace a transistor with high voltages but not higher gain to change the gain you really have to know a lot about electronics but it can be done but far out of reach for the average DJ amplifier repair work to tackle.
The best format for the on tour disco amplifier circuit schematic layout should be arranged so it starts with the physically smaller transistor parts moving up to the larger higher current transistor switching components of the main output.