Yamahaha RX-V679 DC PRT High

[peterwheat]

When the unit was originally plugged in (I bought a house and it came with it, plugged into in wall speakers) the sound was very distorted and muffled at any volumes higher than a whisper. Out of curiosity, I had a speaker plugged in while taking apart, and tested with the unit dissembled. It sounded great, and the voltages at the speaker terminals were normal (read < 0.01 volts). However, as I put it back together, it seemed that the problem reappeared. I'm suspecting a loose connection somewhere possibly? What could cause all the speaker terminals to experience a higher than usual DC voltage?

[budm]

If stand alone testing of the receiver using speakers directly connected to each channel and they sounds fine then I would investigate the house speaker wrings. Some time people will use un-insulated staple for staple down the wires.
Is there also any external speaker switching box?
You can also check the DCR of each house speaker, by measuring each pair of the speaker wires.

[peterwheat]

Originally Posted by budm

If stand alone testing of the receiver using speakers directly connected to each channel and they sounds fine then I would investigate the house speaker wrings. Some time people will use un-insulated staple for staple down the wires.
Is there also any external speaker switching box?
You can also check the DCR of each house speaker, by measuring each pair of the speaker wires.

The standalone testing of the speaker varies as I am putting the unit back together. I tested the in wall speakers using a different receiver and they sound perfect, so the issue is certainly with the receiver.

[budm]

OK, I misread about the speaker hook up, they sound fine when the receiver is disassembled.
Did you verify that all the circuit boards mounting screws are tightened to the chassis, the chassis is being used as ground path for the board ground connections.

[peterwheat]

Originally Posted by budm

OK, I misread about the speaker hook up, they sound fine when the receiver is disassembled.
Did you verify that all the circuit boards mounting screws are tightened to the chassis, the chassis is being used as ground path for the board ground connections.

I have the chassis connected with alligator clips when dissembled. In fact, the issue gets worse with more assembly. Should I just put it back in use taken apart?

[budm]

Originally Posted by peterwheat

I have the chassis connected with alligator clips when dissembled. In fact, the issue gets worse with more assembly. Should I just put it back in use taken apart?

Sound like something's making wrong contacts when putting back together, pinched wires, etc.

[petehall347]

maybe different length screws

[peterwheat]

Originally Posted by petehall347

maybe different length screws

I logged every group of screws so that wouldn't happen, so hopefully not that. Flexing the main board a little causes voltage at the speaker terminals and distorted sound, flexing it back stops the voltage. Poking around for loose components as best I can, but a bit difficult to touch everything while all connected. Can you flow these boards in the oven?

[budm]

Distorted sound on ALL speaker outputs?
If it is then It has to be something that is common to all the amp circuits, I would check the amplifier +/- power supplies Voltages while flexing the board, ground is also common to the circuits so you need to check that too.

[petehall347]

and that -14v i mentioned . or was it minus 24v ? anyway it connects to all the differential amps that control dc offset . i got a bit lost with that as it has a strange circuit .i thought maybe a servo . sorry just on a rant .

[peterwheat]

Haha hopefully no servos buried in here. Watched the -12.4 volt line as I flexed and nothing weird happened. When the problem was occurring, still -12.4. Pressed on all the components I could find with my handy chopstick to see if anything wiggled free and popped the protection, but nothing. Ended up sliding a piece of rubber mat under the main board (didn't block any air holes, but I know it'll heat it up more than usual) sewed it back up, and it's firing away. I'm assuming there's a loose component in there somewhere that is giving me the issue. The odd thing is, the distortion increased and decreased w/ board flex. However, the voltages at the speaker terminals stayed at about 0.28 volts while flexing.

I'm sure it is just a temporary fix for right now, and not the ideal solution. I may pull it open in the future and see if I can't reflow things in the oven, but it works for right now.

For my reference though, where is the amplifier located on the board? It's not the lines coming out of the transformer, right?

[petehall347]

there are separate amplifiers all sharing the same power supply .

[budm]

"For my reference though, where is the amplifier located on the board? It's not the lines coming out of the transformer, right?"
What do you mean?

[peterwheat]

How would I go about checking the main amplifier voltages?

[budm]

Originally Posted by peterwheat

How would I go about checking the main amplifier voltages?

What do you mean 'Main Amplifier'?
See service manual page 136, all the power amplifiers run from +/-61V power supplies and +/- 56V power supplies.

[peterwheat]

Thank you. I'll throw some leads on there and flex it around and see if the problem reproduces itself when I have a little time on my hands. I appreciate everyone's help, very considerate.