Yamaha RX-V1900: 1v8 on SBR output

[Trollet]

Hi.

In these Corona-times I have some time to work on this amp, but I have got myself a headache trying to understand what's going on.
The amp goes in protection, so I have to start it in self diagnosis.

There's 1v8 DC on Surround back right output.
I have pulled both OP-transistors and they measure OK. I have also measured the rest of the semis in circuit and compared them to the other channels.
Of course there are differences, but not more than expected, typical 0v552 - 0v562 drop or so.

Maybe the fault are located in the stage before the OPS ?

The amp are not easy to start up without Yamaha's extension cables, and one can't measure on OPS when the amp is assembled.
So maybe someone have a good clue about what is going on.

BR

Figge

 

[patrick101]

Hi, Figge

Please first check the feedback network circuit components for open circuit.

check key resistors in red color and if no result please measure the voltages.

 

[Trollet]

Thank's I will do that.
The only problem is to fire it up on the bench.
It's not easy without extension cables. I'm not fond of magic smoke...

BR

Figge

 

[Trollet]

Well, the amp are up and running.
Could'nt measure any differences on the bad channel's componets, so I took a shortcut and adopted PCB's from another broken amp. The DSP circuits did'nt work either, it only worked in Direct mode.
Seems like Yamaha does'nt support these amps with software anymore. Are there anyone that knows where to get it?

BR

Figge

 

[deadpool]

Check C280