Onkyo tx-sr674 no sound

[jeff5may]

Just got this av receiver donated to me. The unit powers up and the front panel seems to function as it should. Speaker enable never happens. Popped the case open and nothing looks or smells burnt. No shorted output transistors. The only thing irregular is the high power rails for the power amp section are +/- 30vdc instead of 50 plus.

Tried the usual tricks: unplug for an hour, plugin turn on, turn volume to max, button dance, volume to min, unplug. Factory clear reset. No love. Checked out the self test, all channels fail with NG message.

Anybody have a clue where to look first?

[madan1]

Re: Onkyo tx-sr674 no sound

if no speaker icons on the display - dsp/dts IC dead

[jeff5may]

Re: Onkyo tx-sr674 no sound

Please explain, I don't have any speakers connected to the avr while troubleshooting. The unit comes out of standby, applies half voltage "warmup" to the power amp section. All speaker outputs are failing self test, so the main enable relay never kicks in. I can try injecting different signals (toslink, hdmi, etc.)to see what the avr detects. I'm new to this unit. How should the front panel icons light up under what speaker condition or configuration option possibilities? I know the unit has audessey and auto tune, but nobody left me a microphone or a remote control.

[madan1]

Re: Onkyo tx-sr674 no sound

That icons ( see attached picture ).

Basically, if that icons do not light up ( try different sound modes.. like stereo, surround, dolby, etc. ) the odds are that the fault is in the DTS/DSP chip*. It does not matter if you have any speakers attached or not.


*a TI chip which is known to be defective until revision C (or D?) was released

Indeed those units were sweet deals while the extended warranty was still ongoing.. onkyo would replace the HDMI boards for free without any questions asked.. unfortunately, it was terminated about a year or two ago.


p.s. Just checked the service manual for your unit and the dsp/dts IC is listed as TMS320D707E001RFP250 which is not present in the official list of defective TI chips... so most likely it is something else. In this case, the service menu is a good starting point.

[jeff5may]

Re: Onkyo tx-sr674 no sound

Ok so I found the service manual for the unit and figured out why the amp power rail is low. The power section gets half voltage from the mains transformer when it comes out of standby. Full voltage is not applied until the logic decides everything is okay. I'm assuming that the speaker relays and the power control relay all get signals from the microprocessor to do their jobs. Since every speaker is failing the self-test ( service mode tests display ng), I will begin hunting down digital signals to and from the micro, looking for where the broken link exists.

I found a place to access most all of the relevant signals without dismantling anything. Straight back from the volume knob, there's a stand up pcb that has the toslink and digital coaxial inputs on it. Where that pcb connects to the power amp board, there's a big long connector. It looks like all the pins in that connector are labeled and fairly easy to get to.

[jeff5may]

Re: Onkyo tx-sr674 no sound

Update on my progress:

The digital board that contains the Dolby dsp and the microcontroller on it behaves like expected. The power on signal comes out, lots of speaker relays go to +5 volts a few seconds after pressing the power button. Audio mute and protect lines end up at zero volts during the same time period. So the brain is alive but the muscles are paralyzed.

Looking at the schematic, there is a choke point here:


Besides the logic standby supply, the high current transformer has a couple of extra taps that feed the 22v and 12v supplies. The 22v rail is 8v. Can't see where to check the 12v rail, but it's derived from the 22v rail, so yeah. No relay coils, no relay muscle control. Either some flame proof resistors fizzled or we have a critical capacitor, transistor or diode that fell short or open somewhere close by. I believe the easy way to check this is to unplug and diode check across the rails.

Since the logic and standby supply is good, the standby relay pops and energizes the " low voltage" windings of the power transformer. The " high voltage"winding is active, but the rectifier for it is on the other side of a 24v relay contactor...

[madan1]

Re: Onkyo tx-sr674 no sound

... The only thing irregular is the high power rails for the power amp section are +/- 30vdc instead of 50 plus.

Usually, those receivers have the speaker "ohm" selection option - 8ohms and less ( "4", "6", "4-6" and so on depending on the brand ). When the 8ohm option is selected, the transformer is tapped on +/-X and when the less ohm option is selected - +/-Y where Y<X
So 50V for 8ohm(standard) power and 30V(reduced) seems fine to me. If the value is not correct, it will be logged as a failure in the service manual.

What about the speaker icons on the display? Are they on?

[jeff5may]

Re: Onkyo tx-sr674 no sound

Ok guys, I got sound out of the unit. Relays popping like crazy after power up. The sequence I'm seeing is like the signals I saw on the "digital / dsp / microcontroller" or whatever you wanna call it board. Plug into the mains, standby light comes on. Press power button, the mains relay clicks. After a couple seconds, the 50v enable relay clicks, followed shortly by whatever speaker relays the thing decides to energize.

Previously, I did not see the speaker icons on the display. Standby light lit up when plugged into the wall outlet. Press power button and one relay click, face lit up and acted like it was trying to work. No sound, no flashing lights or protect messages. I got into the service menu, and all the speaker checks came up ng. Not 100 percent sure about the display yet, as the unit is still not buttoned and screwed back together. I'll be doing function testing and etcetera after it has more than a couple of screws per board holding things together.

I did the diode test with my DMM on the little section in the pic, and the DC side looked good. Measuring from the DC side back to the ac input side didn't. Normally, the multimeter will read a single diode worth of voltage drop between a power rail and the transformer. This one read about 1.5v, confirming that the 2 ohm resistor on each transformer leg was dropping extra voltage. So I went to desolder a resistor, and everything literally fell apart.

The two little resistors obviously had a hard life in the unit. They'd heated up and cooled down enough to cook the solder holding them to the pcb. The pads somewhat crumbled off with soldering iron heat and the solder joints were corroded. Had to use some flux to get the smut out.

Rather than taking the whole guts out of the case to rework rotten pads and such, I just got all the ugliness out of the area with the flux and solder after the resistors were out. Some alcohol and q-tip scrubbing followed.

The little red film cap (c9001) and its legs looked good, so I stuck one leg of each new resistor down its PCB holes. I connected the other leg of each resistor to extra fuse holder holes that the pcb traces led to. So now, the resistors are soldered to big huge copper on both sides and should not encounter the same heat cycling as before. The resistor leads are longer, so if the new ones get the same workout, at least they won't cook the board again.

The old resistors both read around 90 ohms out of circuit.

[jeff5may]

Re: Onkyo tx-sr674 no sound

Ok, got her all back together and tested. All of the speaker outputs work great, as well as a bunch of the inputs. Analog and toslink work great! HDMI not so great when it start cold, once the receiver warms up, the HDMI inputs fade in. I don't have a speaker icon array on the front display as madan1 suggested. When the unit is cold, and a surround signal is applied, the front display responds with red Dolby words. If you set the display correctly, the detected format will pop up in text. No sound when cold, turning to hash, turning to garble, fading into splattered music, then finally music.

I saw a bunch of aluminum pimples on the hdmi board while it was apart. That's my guess: audio coupling and decoupling caps getting old and moody. Anyone have the inside story on that issue? Me, I can live with a bunch of RCA jacks and toslink inputs. If I decide to sell it, next user will beat me down for crappy HDMI. Down to the 50 dollars and less price.

[madan1]

Re: Onkyo tx-sr674 no sound

Try heating the DSP chip ( https://www.youtube.com/watch?v=HeboYI2qzhE ). If you do not have the speaker icons, then it has nothing to do with the decoupling caps.