Question about Denon AVR688
My denon avr-688 amp has gone into protect mode after a few months of use, and now after having been shut off for weeks/unplugged, its still stuck in protect mode
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Posted on Jan 02, 2017
It sounds like there is a problem with the differential circuit. The bias I am not sure about, as every unit is different. You should get the service manual to be sure or call Denon and see if they can give you an idea. Good Luck
Posted on Jun 05, 2007
SOURCE: Denon AVR-1508
If your amp looks like it's going to work as normal (ie the front display lights up as it should etc), but then the amp goes into protection mode when the anti-thud circuit times out, then I know what's likely to be wrong.
It's one of the power amplifier channels which has gone faulty.
I just found this out after having this problem with my AVR-1906.
I took the amp apart and de-soldered the suspected channel power transistors (centre channel in my case).....and hey-presto! it fired up as normal (obviously the centre channel would be out of service).
I have ordered the replacement transistors from Farnell (UK) at a miserly cost of around £2-£3 each.
Just waiting for them to arrive.
An alternative is, if you don't use all your channels, take the transistors from a known working but not needed channel and swap them over with the duff ones.
Hope thats of use!
Posted on Aug 16, 2008
Usually when the unit runs for a while before shutting down there are two possibilities:
1) There is a small amount of DC current present that effectively heats up the speaker coils enough to cause a temporary short circuit that kicks in the protect circuit.
2) The output transistors or bias transistors are sensitive to heat and breaking down again causing the protect circuit to kick in.
A few experiments to try:
1) Does the time to shutdown change depending upon the volume level?
2) Is there any background noise coming from the speakers? Listen to a blank tape for example. Is there a hum or any other noise that you would not normally expect?
3) If you have a DC voltmeter, check for any voltage between the speaker lines.
Update this and we'll try to narrow this down.
Posted on Aug 19, 2008
SOURCE: I have a Denon AVR-688
Try to reset the unit: hold "speaker A" and "Speaker B" buttons and power on the unit. Display will be flashing, release the buttons after 3 seconds. If the problem still there, most likely you have bad digital signal processing (DSP) board - send the unit to repair facility.
Posted on May 19, 2009
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