Yamaha RX-V673 power problems

[Coldstream]

Hello everyone,

I'm stuck finding the problems on this Yamaha receiver, i suspect a few things but after messing around the whole weekend it seems like i'm getting on a dead end. Must say, that i've not much experience with these newer devices and i'm a bit rusty.
First of all, i got this device from my friend.. The receiver's fuse went dead when he was just watching a movie.
So obviously, my first step was to get into the diagnostic mode (power sw+info+tone control from my head) and there it went fine with an error P2 (power supply 2, 34L 3.4 volt LOW?) i thought P2 should've been 3.3V so how did it went out that the power there is too low? anyways, before i even could analyze more, i simply removed a lot of dust and now the device won't turn on anymore either.
Previously, even the power led went on, now it's nothing. Obviously i checked all the cable connections.
So, my logic sense seems to be, previously we had the standby transformer/signal going properly, but even that is going crazy now.
For some reason, i can't get out of it properly with the schemes in the Service Manual for proper diagnostics, but if i am testing it right, the 5v and the 12v line both are way underpowered. But to be fair, i am not even sure if i am reading it from the proper points.
I will include the Service Manual as attachment of this post.
To me, the power relay doesn't switch and i think thats because it never gets it's 5v, just somewhere around 3,8v and that might be the problem.
Since i've been looking for problems the whole weekend, it might aswell be that i'm simply overlooking a simple thing as i'm looking way too far ahead.
The AC in is on the VIDEO 2 board, i suspect the problems lay on this PCB too.
If i'm thinking properly, the 5.5v DC comes from T3701 to D3704, end of D3704 gives me 3,8v where i'm sure this should be 5,6v?
Anyways, what also puzzles me is that the 12V line also is somewhere in the high 3v range?

Maybe a fresh pair of eyes, and someone with experience of newer audio equipment can help me out.
I can give measurement results as needed.

The service manual with all the schematics are here:
https://elektrotanya.com/yamaha_rx-v.../download.html

Thanks for any help

[tibimakai]

I don't repair Yamahas, but I know, that they are famous about the main transformer internal fuse going out. Do you get the proper output voltages from it?

[Coldstream]

Yes, i can confirm the main power transformer gets 230VAC and puts out 90VAC. The thing that puzzles me is simply that both the 12v and the 5,5v lines are nowhere near enough.
I guess this is also why the relay doesn't work, but what confuses me the most is that even the front panel doesn't work anymore. No power led, no posibility to get in to the diagnostic mode.
Power around the power switch is in the 3. range, just like the relay. Thats why i suspect i got a problem very early on in the circuit right now.

[goontron]

Check C405. They are a common fault and provides standby voltages in the 240v PSUs. Standby voltages drive that standby relay.

https://www.youtube.com/watch?v=MwvjAtSr5t8

[Coldstream]

Originally Posted by goontron

Check C405. They are a common fault and provides standby voltages in the 240v PSUs. Standby voltages drive that standby relay.

https://www.youtube.com/watch?v=MwvjAtSr5t8

Thanks, but sadly i dont have any C405 in my unit. Any idea which part might provide standby voltages in my unit?

[goontron]

Yes, it looks like they got rid of the dropper for a switch mode PSU.... Finaly.

On the connector CB376 pins 6 and 7 should have 5.5v Does it have such? And is there a voltage between pins 1 and 2?

[Coldstream]

Sadly nothing, i can't get any voltages at CB376. Nothing at all, for some reason

[goontron]

Ah, and thats why. Without that switchmode working, nothing will. what voltage does c3706 have? c3708?

[R_J]

If the 5.5 volts is low, try replacing C3714,C3715. Also replace C3708 (22/50) in the primary circuit

[Coldstream]

Originally Posted by goontron

Ah, and thats why. Without that switchmode working, nothing will. what voltage does c3706 have? c3708?

You want me to check how much voltage goes to it, or how much it holds? sorry for the confusion

Originally Posted by R_J

If the 5.5 volts is low, try replacing C3714,C3715. Also replace C3708 (22/50) in the primary circuit

Looking for replacements right now, i'm just not sure if its only the 5.5v line as i'm also reading odd things at the 12v line, but this can be like above said because it doesn't switch?

[goontron]

^ How much voltage it has while plugged in. Should be around 300v.

Originally Posted by R_J

If the 5.5 volts is low, try replacing C3714,C3715. Also replace C3708 (22/50) in the primary circuit

C3807 is there to start the small PSU, OP. The other two R_J mentioned are for filtering the power coming out of it... If C3708 is bad the PSU wont run, but if C3706 doesn't have power, then nothing will.

[Coldstream]

C3706 is at 315v, C3708 has nothing. Sounds like thats part of the problem, should i replace it?

[goontron]

^ Yes. Sounds like it may well be the problem here.

It would be worth getting a resistance reading across the caps R_J mentioned as well.

[Coldstream]

Sorry, need to correct myself, there is 1.1v at C3708

[goontron]

^ it should be a lot higher... Did replacing it work?

[Coldstream]

Originally Posted by goontron

^ it should be a lot higher... Did replacing it work?

Still busy finding my replacement, will be done very soon. Odd thing is my fluke tells me it's 20.4uF at the capacitor? That makes it seem like it's okay ?

[R_J]

For there to be any real voltage on C3708, the smps needs to be running, if its not running or just trying to start, the voltage will either be very low or nothing.
What is the voltage across C3714/15?

[Coldstream]

Originally Posted by R_J

For there to be any real voltage on C3708, the smps needs to be running, if its not running or just trying to start, the voltage will either be very low or nothing.
What is the voltage across C3714/15?

Both are at 0V somehow..

[Coldstream]

I can't edit my previous message, so sorry for double posting. Just wanted to add that with replacing C3708, the power there is stable 1.3V

Am i right thinking that D3704 gets it's 90VAC from the transformer (which it indeed does) and should put out 90V which goes to C3713, C3714 & C3715.. As it doesn't put out any V that entire part stays dead giving the problems we get? Or am i overlooking anything just here.

[R_J]

T3701 is the standby transformer, it is part of the switch mode power supply, D3704 does not get 90 volts, if it did you would blow up the 25 volt caps!!! It gets about 4.5 volts [at 67khz] not 50hz

You need to measure the voltage across C3706, it should be around 300 volts (220vac input) When measuring voltages in the primary of T3701 you MUST use C3706 (-) or HOT GROUND for ground. it is NOT the same as chassis ground.
when measuring the voltage on C3708, measure across the cap or use the HOT ground
If there is less than 15 volts DC across C3708 it is likely the ic is bad.
Like I said earlier, check the value of R3704, if it is open the the ic likely shorted.

NOTE: if you measure the ac voltage on the primary of T3701 using the chassis ground, it will likely show 90vac. this is NOT the way to check this voltage.
Also be carefull when working in the primary side, itis not isolated. and be carefull around C3706 as it can stay charged when the unitis unpluged. To discharge that cap use a 5K 10 watt resistor as noted in the manual