Question about Denon AVR-3805 Receiver

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How do I test to determine if my preamp is overheating as you state?

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  • Denon Master
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Well I do not know how is on your model, usually it is all on the same mainboard. if its transistors you change the transistors , or there may be a thermic swithch that turn system off.
You should also consider that may be a fault on some of the control chipset.
A problem of this kind won't be an easy DIY unless you have a good background.
I do not have diagrams or schematics for your model, If I find some, I will send them tomorrow.

Leave your denon unplugged overnight, place it away from other devices, until you fix the problem.

Give me your location if you also need directions for local service support.

I will post back tomorrow

Posted on Apr 05, 2008

  • Ginko
    Ginko Apr 06, 2008

    Hi jonny , sorry about yesterday, but it was 1 am here in UK. I am just checking specs for avr 3805 right now, and I can see it has got a 120 watt per channels amp in output. This is one more reason for suspecting it is an amp overheating problem.

    If you watch at the inside of your unit , as from this link, You will notice a large metal cooling plate. This has the function of cooling down the amp final transistors.
    Your Denon had no cooling fan involved, then, unless is not a problem with the cooling plate out of place, you will have to change thermistor and eventually transistors from amp unit.
    Parts involved are:
    Thermistor (approx $20 from Denon supplier)
    Transistors: 2sb1560, 2sd2390 , bu2090 (approx $50 each)
    Another possibility is that power supply started generating more heat than normal, and being very near to thermistor and amp it is causing the unit to shut down. In this case you change the power supply, which costs approx $100.
    All the parts should be tested to locate exactly the problem.

    Here is a supplier selling the replacement in UK and Europe

    Here is a retailer from US serving the rest of the world

    Here is catalog with pictures of the components involved

    Denon AVR3805 is still an expensive device, even if its production had recently been discontinued. This is not going to be an easy fix, you will have to take apart the 3805, test its components, locate the problem among the above, unsolder and solder back components working with precision in tiny spaces.Unless you have a strong background in DIYing electronics, consider also calling out a service.


  • Ginko
    Ginko Apr 06, 2008

    In addition to my last post, in your case the device is working, then there is no need to check the components for continuity.
    What the repairmen will probably do, is changing the thermistor first.
    If the machine keeps shutting down there will be need for checking the temperature on amp unit and power unit to see which one is likely overheating.


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