Denon AVR-1707 Strange Problems

[rahandford]

Trying to repair the above unit but getting a bit confused.
I have checked all voltages and the line labelled +5V_DSP was missing, all other voltages appear to be OK.
All output transistors and the low value resistors on the driver board also test OK.
I have removed all boards and replaced the 5V regulator, then replaced all boards EXCEPT the DSP, Tuner and any video boards (I think this is the minimum required to power the system). The system will power on (5V DSP present) and no flashing or protect errors, but I get no audio. I then discovered that the 5V DSP line has gone down again although there is nothing that I can see on the schematic connected to it!
Am I making some rookie mistake here? Can email SM if it will help but I think that it is too large to attach.
Any help or advice would be much appreciated. 

[singapol]

You can post a link to the service manual or you can extract a page of the relevant schematic you want to discuss to post here.

[rahandford]

http://www.manualslib.com/manual/700494/Denon-Avr-1707.html

[kripton2035]

has the unit already been serviced by someone else ?
if the output transistors and low values resistors are ok, then the problem is mostly ( from experience) in the 78xx regulators of the power board
there are also 78xx (and 79xx) in the supply board.
check the 5v but also the 12v ones. be careful they MUST be isolated from the heat sink.
also please describe the symptoms of the unit (althought I'm pretty sure it's the red light for secure shutdown problem)

[mzacharias]

First thing on a Denon is to do a full reset per the instructions in the owners manual. You'd be amazed how many this fixes. Denons have just always been that way.

[rahandford]

Thanks to all for the suggestions so far.
I have done numerous resets on the unit as per the service manual.
I will check all regulators again, but no I don't get shutdown. The unit stays turned on (green power button) but does nothing.
I will order a new set of insulators for all the regulators just in case there is a problem.
I do have about +60/-60 on the output transistors and processor voltage is present.
Not sure if I have to install all boards for the unit to process analogue signals?
Have also gone through set-up (manual) and do not get a test tone (I only have front R&L connected and configured).
Will report back when I have done all the above, please feel free to shout if you can think of anything else and thanks to all for the support.

[bson]

Is the 5V regulator getting hot?
There may be a thermally induced short.  Is the 5V regulator near its filter caps?  If so the caps might be leaky when warmed up.  The caps leak a bit, causing the regulator to warm up, further heating the caps, which then leak more... and you have a thermal runaway until the regulator either goes into shutdown or fails.
Also, scope the input to the 5V regulator to make sure it's properly rectified and filtered.