Author Topic: Help with Denon Amp needed!  (Read 241 times)

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Offline dezihh

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Help with Denon Amp needed!
« on: December 29, 2019, 11:50:10 am »
Hello,
I have some problems with the repair of my Denon AVR-4311.
Some days ago, I have noticed some smoke from my amp and the the protection was activated. I have disasembled the amp and found out, that one of the 9 amps was responsible for that.
I have noticed, that 2 SMD one the back of the DHCT-C3 Darlington are burned away. Now I have ordered a new pair of the Darlingtons DHCT-A3 and DHCT-C3 but I have some problems wirh replaceing the burned SMDs.
Attached you find the circuit. I think the manual is wrong or incomplete.
1.) You see directly in the circuit diagram attached to both of the transistor a diode and a resistor (see arrow). In real, these are only existing for DHCT-C3. On the corresponding foil (attached / arrow) there is a diode and a Z-diode printed, but no resitor.  It seems for DHCT-A3 there is in real no suchg diode, resistor, z-diode etc... (see foil) picture. I am confused... :-//
2.) Even if this resitor and diode is mentioned in the plan, there is no information about, what kind of resistor and diode are used.
I saw, that other Amps from Denon have a similar circuit. So, could you please help me, to identify the diode and the resistor?
Thanks in advance...
 

Online SpecialK

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Re: Help with Denon Amp needed!
« Reply #1 on: December 29, 2019, 03:29:00 pm »
So a couple things:

1 - I believe there are probably 9 nearly identical channels. I belive they are modular. Have a peek at one of the others.

2 - D105 and Z101 are listed on the schematic.  D105 is a KDS160.  Z101 is presumably a PRF18BB471QB5RB temp sensor, I can't see the full part number as that's been cropped from your picture.

3 - There is no resistor from what I can tell

https://pdf1.alldatasheet.com/datasheet-pdf/view/422249/KEC/KDS160.html
https://www.murata.com/en-us/api/pdfdownloadapi?cate=luPTCforTempeSenso&partno=PRF18BB471QB5RB

 
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Offline tooki

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Re: Help with Denon Amp needed!
« Reply #2 on: December 29, 2019, 05:23:54 pm »
Look at the schematic again carefully:

1. The diodes and resistors in DHCT-C3 and -A3 (Q108 and Q109) are inside the box (with pin numbers) that forms the darlington. So they are internal to the darlington package — that's why they have a box around them. If you google those part numbers, you'll see the symbols for those components including the diodes and resistors.

2. As SpecialK said, D105 and Z101 (the SMD components you pointed to on the PCB layout) are expressly listed in the schematic, so they're definitely not the internal diodes and resistors in the darlingtons. Find them on the schematic you have, and you'll find them both listed with part numbers.

3. If you look at other zener diodes in the schematic, for example D106 and D108, you see that they aren't using the Z component designator for zener diodes, so you can deduce that Z101 is something other than a zener diode.
 

Offline andy3055

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Offline David Hess

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Re: Help with Denon Amp needed!
« Reply #4 on: December 29, 2019, 05:52:48 pm »
All Darlington transistors have a base-emitter shunt resistor across the output resistor for removing leakage and charge from the output junction, so the resistor is built in.  Usually a resistor is also included across the base-emitter junction of the input transistor but it is not strictly necessary.

The diode is built in because it is part of the temperature compensation for the bias.  Making it part of the transistor works better than mounting externally.
 
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