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Old 26th February 2006, 04:27 PM   #1
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Default Denon AVR2803 goes into protection

Hi all,

This AVR was damaged by a lightning strike. The symptons are it will not switch on and remain on, but it pulses on and off. Something is causing the unit to go into protection mode. I have disassembled the unit and checked every diode & transistor I could find, no problems found. The output stages use MP15P and M15N complimentary Darlingtons.

I have the schematic for this unit, together with the headache of trying to decipher minute printing and track layouts which go from one board to the other.

If the unit would only remain switched on long enough to do some trouble-shooting, the task would be much easier. I can find no reason for the unit going into protection, but obviously something is amiss. There are times when the unit will actually switch on and remain powered for a few minutes, the display comes on and then I can select a FM station on the tuner, with audio. If I press any button on the remote however, the ubnit switches off and begins to pulse again.

Any one here with experience in repairing this unit?

-Eric
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Old 26th February 2006, 04:48 PM   #2
anatech is offline anatech  Canada
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Hi Family_Dog,
One question for you. Are you very experienced in audio repair?

Okay, two questions. Do you have a variac?

-Chris
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Old 26th February 2006, 04:55 PM   #3
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Hi Chris,

Good idea, I do have a variac, never thought of using it.

I am more into tube gear than solid state, just have to put on the thinking cap when I work with s/s. Tube gear is much simpler! Yes, I can go into detailed circuitry and have a scope etc.

-Eric
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Old 26th February 2006, 06:08 PM   #4
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Hi Anatech,

Thanks for the suggestion. I have already done something similar, by grounding a relevant jumper which over-rides the protection circuitry. The trouble with this receiver is that you cannot get to the components for measuring purposes while it is assembled. I have connected just the basics and and carrying on from there. Denon certainly will not win any design award for the way they have inter-connected the different component boards in this receiver.

Still investigating, will report back on what I find.

-Eric
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Old 26th February 2006, 06:13 PM   #5
anatech is offline anatech  Canada
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Hi Eric,
That goes for all AV recievers. Too much darn stuff in there!


I killed my previous post so someone else doesn't get themselves into trouble.


-Chris
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Old 26th February 2006, 06:19 PM   #6
MikeB is offline MikeB  Germany
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Quote:
Originally posted by anatech


I killed my previous post so someone else doesn't get themselves into trouble.

-Chris
Too late, i've already read it...

About the receiver, my guess is that the micropocessor got a defect or the ROM partially erased, crashing the computer. Maybe some watchdog is then shutting down the whole thing ? Let's hope i am wrong...

Mike
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Old 26th February 2006, 06:22 PM   #7
anatech is offline anatech  Canada
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Hi Mike,
I wouldn't be worried about you.

I think there is some protection triggering the set off. The uP seems to be operating okay from the description.

Eric, check for blown grounds between the antenna jack and RCA grounds. Also to chassis.

-Chris
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Old 26th February 2006, 06:43 PM   #8
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Hi Chris,

The grounds are all OK, there is no obvious lightning damage to be seen anywhere. The receiver does use micros, but unless a 5v line went high or something, I doubt the micro has suffered. It could still be damaged, of course, lightning does weird things.

The various power supply voltages all seem to be there, although I am still in the process of measuring all the different volltages, which are spread over two boards.

Getting late Sunday night here so I have called it a day before I do something stupid. Tubes are Oh, so forgiving, but solid-state is not.

-Eric
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Old 26th February 2006, 07:18 PM   #9
anatech is offline anatech  Canada
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Hi Eric,
Quote:
Tubes are Oh, so forgiving
So true ...
Quote:
Getting late Sunday night here so I have called it a day before I do something stupid.
Great idea. Good luck tomorrow!

-Chris
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Old 1st March 2006, 05:36 PM   #10
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Ok, here is the latest update on the Denon repair attempt.

I powered up slowly with a variac while monitoring the +54V & -54v collector voltages, no mean feat because Denon buries all components in completely inaccesible places.

Bringing the variac up to 100v produced no results other than suitably low voltage readings and I had to advance the variac to just under 200V (our AC Mains is 240V nominal) before the AV showed any signs of life. Advancing to just over 210V brought the inimitable protection relay click-click, which indicated something was trying to power the AV down. But nothing was showing any signs of distress and the panel FL display came to life. I fed a suitable audio input to the AUX In, and I got perfect sound from only one channel. So we have a faulty channel, although the Output Darlingtons seem to test OK, as far as I could test them with a DMM. They are completely inaccesable in the depths of the Denon, but I did measure them when I had the unit lying in pieces earlier.

I measured the voltage across the AC Power-on relay coil, which should have been 12v but was less than 8v. This implies a fault in the one audio channel is attempting to power down the AV. My next task is to trace the path from the PS Unit backwards to the offending audio channel, easy, huh? Not so! This link goes from board to board, ending at a Microprocessor. I have to assume the CPU is healthy as all the other AV functions do seem to operate correctly. The fact that I cannot reach 90% of the components does hinder my progress but I feel I am getting there.

-Eric
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