|
|
Post by frankusb on Aug 2, 2023 20:19:52 GMT -5
Hi, I have an Onkyo TX-NR708 that for the past 8 years has been working nicely. A few weeks ago, I couldn't turn it on, the standby light was out. Unplugging and plugging back in results in the standby light flashing once and then remaining out (I've since measured it at around 18ms). I started by checking the standby power supply and found a dead capacitor but it was not relevant (C922). I followed +12VDG1+SUB to the main microprocessor and checked it's power supplies (Q7032 and Q7029) and they are right where they should be with no ripple. Is there any way to get any diagnostic output from the microprocessor? There are 3 serial ports but they are for control, XM and iPod dock. Is there something else I should be looking at? Thanks. Attachments:
|
|
|
|
Post by tjmotter on Aug 3, 2023 10:27:15 GMT -5
That light also acts as a diagnostics light and if I recall correctly, a flashing light indicates that you have a blown output channel. At startup, the Main CPU will attempt to power up the output stage but will be monitoring voltage and current flow. If it detects any thing out of spec, it will shut the power rail down and flash the standby light.
The easiest way (I have found) is to use a meter to check all output transistors. Invariably, one of those will measure differently than the others which will point you to the problem.
I suspect you will find that one of the capacitors has failed causing a couple of resistors and transistors to blow. The main output transistors may (or may not) be ok but using the Front Left circuit as an example, check: C5100 (this is the problem capacitor), R5420, R5280, R5270, R5470, Q5430, Q5250, Q5440, Q5260, C6041, Q6034, Q6044 and R6074.
HTH
Todd
|
|
|
|
Post by tjmotter on Aug 3, 2023 12:09:20 GMT -5
I should note that all of the components I describe above should reside on the vertical pre-amp board. The final output stage sits on the mainboard but the pre-amp board sits in a series of connectors and stands straight up. You will need to remove the screws. A long phillips screwdriver works best and I find that it is easier if the screwdriver is magnetized because the screws are a little difficult to get back in if you can't get them to stick to the screwdriver.
Another (perhaps easier) test is to check the resistance of each of the 5W resistors. Each output stage has a 0.22 ohm 5W resistor that connects the PNP/NPN output on the mainboard. These are pretty easy to see since they are large white blocks with 3 pins that stick straight up on the board. The center pole is the output and each of the end poles connect to the two power transistors for that circuit. One half of these will typically blow and they are easy to check. Using the Front Left circuit as an example, the resistor should be labeled as R6100. Simply measure the resistance from the middle to each of the outer poles and look for one that is an open. 0.22ohm's is basically a piece of wire so you should be reading close to 0ohms of resistance.
HTH
Todd
|
|
|
|
Post by frankusb on Aug 4, 2023 10:04:01 GMT -5
I apologize, I was unclear. The standby light flashes once for about 18ms after plugging the receiver into an outlet and then remains out. I have to unplug the receiver and replug it in and the process repeats. The standby light is not steady flashing.
|
|
|
|
Post by frankusb on Aug 16, 2023 9:12:26 GMT -5
Is there any way to diagnose the main processor boot sequence? Or is there anything else to check, clocks?
|
|
