Denon AVR-1912

[NickLoC]

Re: Denon AVR-1912

From what? The voltage regulaors?

[NickLoC]

Re: Denon AVR-1912

I know it's not the amp board audio transistors or resistors. Tried two amp boards. I know it's from a pioneer , but the output chips are the same and I adjusted dc offset to denon service manual specs. Kind of stumped here. The pop in the audio when i turn it on leads me to believe it's not a fault in the protection circuit, but elsewhere. Any ideas here? I'd really like to get my surround system up and running again.

[ferroman244]

Re: Denon AVR-1912

The pop is DC offset. Does it do this on all channels?

The offset occurs, for some yet unknown reason, because the conduction of the faulty channel(s) output transistors is not the same- one is powered from the positive supply and the other from the negative supply, and when all is well, in a perfect world, the conduction cancels to yield 0 volts DC offset. That unequal conduction can be from an offset voltage applied to the output stage from a previous stage, the transistors themselves, unequal power supply voltages (maybe), or something like that.

Someone mentioned the main filter caps. Did you check both rails of the power supply to see if they were equal, both with no signal and as you increased the signal? If there seems to be a problem there, be sure to carefully check the caps for value and the bridge rectifier diodes. One may be open, causing increased ripple and hum, and poor voltage regulation as the load is increased.

I don't have the schematic to look closer.

[NickLoC]

Re: Denon AVR-1912

Thanks. With check the area on the speaker board. How do i check the main rail voltage?

[ferroman244]

Re: Denon AVR-1912

Very, very carefully, of course.

Can you get to the rectifiers easily? I imagine they will be close to the main transformer and filter caps. Maybe one lead on them is marked with a + or -. Measure to the metal chassis, if you can't find the center tap of the transformer.

Another way is to be extremely careful and measure the voltage on each transistor lead. The transistor with positive voltage should have one lead that measures what the rated supply voltage is supposed to be, say + 50 volts or so. The other transistor, connected to the negative rail should have a lead that measures the same as the other rail, say -50 volts. You need the schematic to get the exact value.

Again, I don't have the schematic, but I am assuming it uses discrete output transistors in a fully complimentary configuration.

Be careful. It's easy to let a probe slip, and short the transistor leads together or to something. That almost always means blown transistors and stuff that you didn't have a moment before.

I'll look back through the thread for a schematic link.

[cheffner]

Re: Denon AVR-1912

Adjusted the DC mv to spec from service manual. It's better, but still cuts out. Looks like DC detect is on amp board, but doesn't it get power from the regulators on the speaker board?

Can I ask where you found your service manual?

I am looking for the service manual for the Denon AVR-3808CI to help fix the "blinking red of death".

Any help would be greatly appreciated.

Cheers,

Christopher

[puntt]

Re: Denon AVR-1912

Can I ask where you found your service manual?

I am looking for the service manual for the Denon AVR-3808CI to help fix the "blinking red of death".

Any help would be greatly appreciated.

Cheers,

Christopher

Hi hope it helps.
http://www.hifiengine.com/manual_lib...avr-3808.shtml

[williakz]

Re: Denon AVR-1912

Can I ask where you found your service manual?

I am looking for the service manual for the Denon AVR-3808CI to help fix the "blinking red of death".

Any help would be greatly appreciated.

Cheers,

Christopher

How did you make out with your 3808 problems? I have a unit with a bad main board (HDMI, Ethernet, subCPU, etc.) that I've parted out. Let me know if you need anything to get yours up an at 'em. Good luck.