Denon AVR-1912

[NickLoC]

Have this receiver and with no speakers connected it would power up and flash blue with display on the screen then click and shut down flashing red. Traced it down to the front right channel having blown STK chips and a bad Transistor. Replaced all three parts with OE parts. Amp now powers on and stays on with no speakers connected. With front left and front right speakers connected amp acts like when I first got it and shuts down. With just the left front connected it out puts sound. But after turning it up past -30db it shuts down again and flashes red. Any ideas what else could be shorted? Could another bad part in the right channel cause a shut down even with just the left connected?

[NickLoC]

Re: Denon AVR-1912

Anyone have any advice?

[budm]

Re: Denon AVR-1912

There is circuit that detect for DC at the output of the amplifiers and also detect shorts or over current of the output sections. I would check the DC voltage of each amplifier output to see what kind of DC offset they have at the output feeding the speaker protection relays.
Did you find service manual for this unit?

[rievax_60]

Re: Denon AVR-1912

Anyone have any advice?

STK parts usually have external emitter resistors like in discrete designs.
These resistors often blow open when the STK fails short circuited.

[NickLoC]

Re: Denon AVR-1912

Thanks for the info. No I do not have the service manual. Are the resistors on the amp board? And if those are bad on the right channel will that cause the amp to shut down even if that channel is not connected?

[rievax_60]

Re: Denon AVR-1912

Thanks for the info. No I do not have the service manual. Are the resistors on the amp board? And if those are bad on the right channel will that cause the amp to shut down even if that channel is not connected?

They should be very close to the STK part. Usually large white ceramic and likely to be two resistors combined in a three leaded part. And also low value like 0.22 ohm.
When these resistors blow open or go party high in value, all might seem ok until audio signal is applied. The protect fault sensed can be DC or overload.
What do you mean by "not connected"? What is happening when it is connected?

[NickLoC]

Re: Denon AVR-1912

When you connect both speakers to left and right, amp powers on, flashes blue then shuts down and flashes red. With just left speaker connected, amp stays on and plays audio until you turn it above -30db, then shuts down again. Will have to check those resistors when I get some free time,

[NickLoC]

Re: Denon AVR-1912

All 7 resistors are bad on that channel. Got the replacements just need to install. Got slightly large wattage resistors this time. This shouldn't change the sound any right? Or should I change both left and right side?

[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?

[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

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'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

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?

[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

[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

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

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

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.

[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?

[ben7]

Re: Denon AVR-1912

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