Denon AVR-1912

[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.

[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

[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

[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.

[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

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

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.

[NickLoC]

Re: Denon AVR-1912

From what? The voltage regulaors?

[ben7]

Re: Denon AVR-1912

Sounds like there still could be some sort of DC offset issue

[NickLoC]

Re: Denon AVR-1912

Also when i turn on the amp, once the relay kicks in there is a pop on the speakers. Not really loud, but you can hear it. Could that be a capacitor issue? How likely is it that those large filter caps are bad?

[NickLoC]

Re: Denon AVR-1912

Here is a pic of the speaker board and regulator board. Is this what your talking about? Could one of those regulators be bad? Also i checked the mv DCC voltage on the two front channels while running and seems to kick out when it hits 60mv.

[ben7]

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?

Ah, so it is on a different board.
It could have gotten damaged from the previous amplifier fault.

Also, check that the main filter capacitors have their rated capacitance. Try measuring the voltage on the amp's power rails, and see if the voltage dips. Just wondering if it could be a supply issue, amp issue, or protection circuit issue.

[NickLoC]

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?

[ben7]

Re: Denon AVR-1912

Swapped out for the working amp board. Still same thing. Get volume above a certain level and amp throws a DC detect error. If i reset amp, will work at high volume for couple of mins, then DC protect again. Gonna try to set DC idle current for each channel. Still wondering if it's a component on the speaker board or voltage regulator board

Could be improper thermal coupling, when parts heat up, their values change, and that could cause an increase in the offset voltage.

Question. Is the protection circuit on the amplifier board?

[NickLoC]

Re: Denon AVR-1912

Swapped out for the working amp board. Still same thing. Get volume above a certain level and amp throws a DC detect error. If i reset amp, will work at high volume for couple of mins, then DC protect again. Gonna try to set DC idle current for each channel. Still wondering if it's a component on the speaker board or voltage regulator board

[NickLoC]

Re: Denon AVR-1912

So it's been a long time posting on this one. Posted another one on a pioneer amp i have, think it's a bad hdmi board. Any way, just out of curiosity i checked the amp board of the pioneer and it's almost identical. Go figure. So i hooked it up and the amp powers on and works. Can turn the volume up to -8db before it cuts out now lol can the speaker board where the relays are have a short? I have a spare pioneer amp board I'd like to try, as i think this one is bad. When i had it in the pioneer before the hdmi board issue, the amp would randomly cut out as well. What do you think?

[tibimakai]

Re: Denon AVR-1912

I'm a beginner here also, I have just repaired a couple of receivers with the help from this forum.
I'm repairing, mostly LCD TVs.
I have learned, that it's a good idea to print out(or look on the monitor at the amp schematic) the amp schematic and go over all the components and make sure that they are all OK.
Some say, that it's a good idea to replace all the transistors.
There are some pretty good videos on Youtube too.

[NickLoC]

Re: Denon AVR-1912

I checked them out again and they were ok. I'll check again. If they are ok what else could be burned out?

[tibimakai]

Re: Denon AVR-1912

I have just blew up a bunch of components, after I have replaced them on a Yamaha receiver. I have blew it up after connecting the speakers.
Lesson learned. Check all components and only then turn it on. You may have blown again the STK.

[NickLoC]

Re: Denon AVR-1912

Ok, so I replaced the resistors and it still shuts down with a blinking red light. I then checked the speaker board and found several 10ohm resistors blown. SO I replaced all of them. Still shuts down. If I disconnect the wire connector from the amp board to the speaker board, it powers up and stays on. Does it sound like I still have a short some where on the speaker board?