Onkyo TX-NR708 standby light

[frankusb]

Hi,

My Onkyo TX-NR708 when plugged in the standby light turns on very briefly than goes out.

I measured relative to GNDMPU
1-MPOWER - 0.0002V
2-+12VDG1+SUB - 11.7V
3-GNDMPU
4-+12RL - 0.318V
5-/POFF - 10.49V

I found that C922 was out of spec and replaced it with a used replacement but no change. I feel like +12RL should be driven by T902 always under normal operation. Is that correct?

[frankusb]

Re: Onkyo TX-NR708 standby light

I've probed a bit more. There is 12.0V across C922 and 11.5V across C930, so it seems the transformer T902 and diodes are OK. I also find 12.0V on the other side of R922. I previously missed D926 that seems to block the voltage to +12RL. I'm not sure what +12RL is for but I guess it's not an output from the board.

[frankusb]

Re: Onkyo TX-NR708 standby light

C930 was on the lower side of what it is rated, not much but I swapped it with one that measured closer to ideal. No change.

+12VDG+SUB feeds two regulators Q7032 +5VST and Q7029 +3.3VST. I measured 5.6 across C7047 which seems high. C7028 measures 3.3 on the money.

I'm not sure where to go from here. It would be nice to get some info from the Q7020 processor. I found 3 serial ports but they don't seem like they would have diagnostic information on them. This processor drives LEDSTBY.

Any ideas?

[frankusb]

Re: Onkyo TX-NR708 standby light

Well that was a dead end. Q7032 is a 5.6V regulator. I checked the output of both Q7032 and Q7029 with a scope and they seem very well regulated, no ripple to speak of.

[frankusb]

Re: Onkyo TX-NR708 standby light

LEDSTBY is high for 18ms.

[Crystaleyes]

Re: Onkyo TX-NR708 standby light

This series of home theater systems is plagued by various issues.
Although I've not worked on many, I have opened a few.

I scrapped one for parts after the problem was a microproscessor which after importing from China, wouldn't have been cost effective and with the output transistors are expensive over here, time had run out for that particular unit.

I've seen the 'stuck in standby' problem resolved tthrough doing a reset by pressing certain butons on start-up, but you will have to research as to which buttons are for that model.
It is surely in the service manual (I take it that you have that?)

Have you checked that the relays are switching ok, and actually making contact?

Another common start-up problem is related to issues on the HDMI board.

You'll probably find some good advice on the Onkyo section of the Home Theater forums;

https://www.hometheaterforum.com/community/tags/onkyo/


Good luck

[frankusb]

Re: Onkyo TX-NR708 standby light

I've seen the 'stuck in standby' problem resolved tthrough doing a reset by pressing certain butons on start-up, but you will have to research as to which buttons are for that model.
It is surely in the service manual (I take it that you have that?)

Have you checked that the relays are switching ok, and actually making contact?

Thanks. I can't do the reset as it requires the standby light to be on which this system does not get to. The relays are not being energized by the processor, only standby voltage is present but no standby light. I do have the service manual.

[Crystaleyes]

Re: Onkyo TX-NR708 standby light

Just a quick one, but considering that the unit is essentially dead, it wouldn't hurt to verify the power supply. You might wanna check everything including the large filter caps.

Something appears to be pulling the standby voltage down on start-up, so maybe see what else is in the stand-by circuit?

Even without the stby led, have you 'tried' to do the reset?


If you can share the service manual then I'm sure you'll get more help in finding the solution.

[frankusb]

Re: Onkyo TX-NR708 standby light

The service manual is here.

I believe I have verified the standby supply as well as the two regulators it feeds and they are good. Why do you say it's being pulled down? My thought is that the standby LED is controlled by the microprocessor and it is turning it off.

I did try the reset and did not get a response.

[Crystaleyes]

Re: Onkyo TX-NR708 standby light

The service manual is here.

Why do you say it's being pulled down?

I say that because you momentarily have the juice to power the LED, but then you don't.

Voltage will always push a current via the 'path of least resistance' to ground, so perhaps something is a quicker/shorter path than your standby LED? Something quasi-shorting?

The voltage must be being diverted somewhere.

[Sam Scarbo]

Re: Onkyo TX-NR708 standby light

I have got this problem before on my TX-SR606 after I shorted something by accident. I fixed it by replacing a 3A fuse near the power transformer.

The +12RL should be about 12V all the time. Check fuses F2001 and F2000 to see if they are blown.

[frankusb]

Re: Onkyo TX-NR708 standby light

I say that because you momentarily have the juice to power the LED, but then you don't.

Voltage will always push a current via the 'path of least resistance' to ground, so perhaps something is a quicker/shorter path than your standby LED? Something quasi-shorting?

The voltage must be being diverted somewhere.

If it was the case that a short existed, wouldn't you expect to see Q7032 and/or Q7029 out of spec?

I have got this problem before on my TX-SR606 after I shorted something by accident. I fixed it by replacing a 3A fuse near the power transformer.

The +12RL should be about 12V all the time. Check fuses F2001 and F2000 to see if they are blown.

Thanks. I did check F2000 and F2001 and they are fine. Wouldn't you expect +12VRL to only be on when the main relay is on?