| Electronics > Repair |
| Pioneer VSX520 No power |
| << < (5/5) |
| smk279:
I replaced the bad transistor but it still doesn't power on How do I test the transformer |
| MathWizard:
Well IDK this model, but it might need some signal from another PCB, to be able to power up fully. What all chips are on the PSU PCB ? At some point make sure they all get power. It could be mainly just discrete BJT circuits, I should find the schematic. Go on youtube and watch some stereo PSU repair video's. You can check a lot of stuff un-powered, with just a DMM. And I'd solder on a some test wires, like on the GND of the secondary side of the transformer, maybe after a rectifier. Resistance on a DMM can sometimes be good enough to check a transformer, but yeah I know what to expect. The best test for your transformer, is just plug in the PSU, and measure the transformer AC output, and it should lead right to rectifier circuits, and have a pretty stable DC level, a few volts ripple maybe. I need to look at the schematic. Also, if time is no concern, you could remove most of the caps, at least the electrolytic ones, and check them. Then with them out of circuit, un-powered with a DMM, you probably would find most stuff that could gone wrong on a linear PSU, like some diode or resistor. or bad BJT. Are any of the relay's part of the power supply circuits themselves ? They go bad, but also need control signals, that probably comes from the main MCU somewhere on another PCB. But it's not hard to make a little circuit to turn on a relay, if that signal was all that's missing. |
| Laval:
I have worked on a Pioneer VSX-832, it looks like the VSX-520 has many similarities. On the 832, the AC line cable is connected to a board which is nothing more then a small switch mode power supply that is always energized. It powers the standby system. On the small SMPS bord there is a relay which energizes the primary winding of the main power supply's transformer when the amplifier is turned on. Make sure that relay is working. Also check if you have AC on the SMPS. There should also be some connector on the SMPS that runs to other boards. On the 832, the pinout of all connectors is written on the boards so you should know which is +12 V, GND, etc. Assuming you have AC, make sure these voltages are OK. Also, you said you changed some of the output power transistor, make sure you check the emitter resistors. They should be close to the transistors and they usually have a value below 1 ohm. Make sure they are neither short nor opened. It would help to have clear pictures of all the boards. Also clean these boards. There is useful information written on them. EDIT: 1. When I get back from work, I'll post annotated pictures to be clearer. The relay and it's driving circuit can be tested off line using a bench power supply. If it works, then the controlling circuit (MCU/MPU) will need to be investigated. 2. If you test the SMPS power on relay it would be a good thing to do it with all the other boards disconnected. Forcing a power on may blow more things up. It is quite possible that the controller board (the one with a processor) is still detecting a fault and doesn't want to power the device. |
| eetechTom:
The blue resistor to the left of the brown capacitor you initially thought was shorted appears to be burned. Have you measured its value? If one of the output transistors failed I would be sure to check the transistor in the previous stage as well. |
| Laval:
Here is a couple of pictures of the VSX-832 standby supply. The red circle is the AC line, the yellow is the transformer's primary winding. The blue circle is the connector from the control board IR detector (MPON) and power on switch (SWPON). The white and black markings on the other side are the relay switch which connects the AC line to the transformer primary when on and the relay's coil. Applying 0.9-1.0 v on the MPON pin of the connector when AC is connected will trigger the relay if it works. Your board may be different but it should follow the same logic. Like eetechTom said, it is important to test the resistor near the output transistors just don't forget to de-solder one leg to do it. If the standby relay bord works, it would be wise to check the transistor/resistors of the previous stage as well. I hope this helps. |
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