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Old 10-28-2020, 07:10 AM   #1
FrozenHaxor
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Default Denon AVR-X2000 no audio after blown channel, no bias current.

Hello,

I'm repairing a Denon AVR-X2000 that has blown both FR channel output stage transistors. Upon replacing the transistors (Q416 and Q422) witch a matched pair and replacing both burnt 22Ohm base resistors (R458 and R483) the unit powers up and I was able to set idle current to spec (8mV on test points) across all channels except for the FR channel that had a problem, it tests 0V and I'm unable to adjust that at all. The transistor (Q421) which regulates the bias current tested okay (it sits between the big transistor pair). Also I'm unable to produce any audio from any channel. I have tested all main power rails and they check out fine, output transistors are getting their positive and negative ~40V rails as well.

Has someone came across such issue? I would assume that audio would come out of any other channel except the one that still doesn't fully work. Could something upstream that produces the low level signal be blown? Never came across that. Any hints appreciated, apart from amplifier block, the rest of the unit is pretty much impossible to test due to joined board construction that pretty much make a full box with no access.

I have uploaded service manual to my private server due to attachment size limit: http://frozenhaxor.pl/avre400.pdf
















Thanks!
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Last edited by FrozenHaxor; 10-28-2020 at 07:21 AM..
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Old 10-28-2020, 08:50 AM   #2
R_J
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Default Re: Denon AVR-X2000 no audio after blown channel, no bias current.

If the base resistors were open, I would check all the other resistors and transistors in the drive circuit, also are the output emitter resistors ok?
Check the voltage at the common point of the output resistors (dc offset) this should be near 0 volts, if it is not it will not allow any of the speaker relays to connect to the speakers, so no audio from any channel.
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Old 10-28-2020, 09:04 AM   #3
tibimakai
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Default Re: Denon AVR-X2000 no audio after blown channel, no bias current.

I'm pretty sure, that there are more components that are bad.
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Old 10-28-2020, 03:46 PM   #4
FrozenHaxor
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Default Re: Denon AVR-X2000 no audio after blown channel, no bias current.

Quote:
Originally Posted by R_J View Post
If the base resistors were open, I would check all the other resistors and transistors in the drive circuit, also are the output emitter resistors ok?
Check the voltage at the common point of the output resistors (dc offset) this should be near 0 volts, if it is not it will not allow any of the speaker relays to connect to the speakers, so no audio from any channel.
Thanks, turns out I missed one emitter resistor pair. Not sure how, must have measured only one pair by mistake. Everything works fine now, bias current is set and regulating properly with temperature. Audio output is good.



Quote:
Originally Posted by tibimakai View Post
I'm pretty sure, that there are more components that are bad.
If I didn't know that, I wouldn't be posting
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Old 10-28-2020, 04:05 PM   #5
R_J
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Default Re: Denon AVR-X2000 no audio after blown channel, no bias current.

Glad to here you have it working.
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