Denon AVR-1906 Protection mode

[Krzysiek_EL]

Hello

I have a denon reciver that i can't get out of protection mode and need some help.

It went into protection mode after listening to music and i smell something burrning while that happend.
I took it to service shop but after 7 weeks i've lost my patience and got it back. They said that center channel was blown. They replaced the 3 output transistors, four 0.22ohm resistor and 1 zener diode 6.2. It is still in the same condition as befor. After switching on the protection kicks in after 2-3 seconds and it's blinking red.

What i've measured so far :

Voltage regulators:
7915 in -25 out -15
7815 in +24,9 out +14,7
7805 in +11 out +4,95

Transistors :
FL 2SD2390 B+1,0 C+51,6 E 0,0 2SB1560 B-1,0 C-51,6 E 0,0
SL 2SD2390 B+1,0 C+51,5 E 0,0 2SB1560 B-1,0 C-51,5 E 0,0
C 2SD2390 B+26,3 C+51,4 E+25,0 2SB1560 B+24,0 C-51,6 E+25,0
SR 2SD2390 B+1,0 C+51,4 E 0,0 2SB1560 B-1,0 C-51,5 E 0,0
FR 2SD2390 B+1,0 C+51,5 E 0,0 2SB1560 B-1,0 C-51,1 E 0,0
SBL 2SD2390 B+1,0 C+51,6 E 0,0 2SB1560 B-1,0 C-51,5 E 0,0
SBR 2SD2390 B+1,0 C+51,5 E 0,0 2SB1560 B-1,0 C-51,5 E 0,0

There is still something wrong with the center channel.

I've tested all test points in all channels, all in 1,8-2,0mV

Can anyone help me what to do next?

 

[Nigel Goodwin]

You need to repair the entire amplifier channel, not just the small output section of it you posted.

DC coupled amplifiers are notoriously difficult to repair, as if you fail to replace one faulty component, they might all blow again.

 

[Krzysiek_EL]

Let me be honest, it is my first time with repairing electronics.
I thought that it was the entire channel. On the upper portion is the main board and lower the pre amp for the central channel.
I have the service manual for this reciver. I'll attach the whole schematic.
Can you please guide me what to check next?
I've already checked all the components from the first attachment and they seems ok.

 

[Nigel Goodwin]

That's still only the output stage, the rest of the power amplifier (probably most of it) is on the preamp board.

 

[Krzysiek_EL]

I'm back on the preamp board. I've found 2 blown resistors and replaced them. R509C and R511C.
Now im getting +48V on emmiters in central channels. Good thing that it didn't blow up
I've measured the resistance between the legs of Q501-504 transistors and it seems that Q502,503,504 are faulty becasue there is 0-100 ohm and on the good channel there is "infinity".
Going to replace all three.

Maybe a stupid question but can i power up the reciver without the preamp board?