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Denon DRA-300 Dead Left Channel
Denon DRA-300 Dead Left Channel
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Old 19th September 2019, 06:03 PM   #1
22asd is offline 22asd  United States
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Default Denon DRA-300 Dead Left Channel

I recently found our old family receiver and put it in my room only to find out that the left channel was not working.


I opened it up to find that the left channel fuse was blown. I could not seem to find a match for that fuse type, but I found some PICO fuses in China that matched the 4A 125V.


After soldering it to the bottom joints of the fuse holder and regaining the connection, the channel still does not work, maybe something further upstream is damaged?


I have 0 experience with receivers or audio and could not find a schematic for the DRA-300. Just hoping someone might have a suggestion or schematic. I got a scope, meter etc
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Old 19th September 2019, 07:21 PM   #2
Mooly is offline Mooly  United Kingdom
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Denon DRA-300 Dead Left Channel
We really need to see a circuit to advise in detail, however basic checks would be...

1/ Check to make sure the replacement fuse is still intact (measure it) and that it has not silently blown.

2/ Try the unit with headphones while leaving the speakers disconnected.

3/ Try more than one input.

4/ If we assume the unit is DC coupled then you should check to see there is no DC offset present on the faulty channel speaker feed. Trace this feed all the way back to the PCB.
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Old 19th September 2019, 11:37 PM   #3
22asd is offline 22asd  United States
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Imgur: The magic of the Internet
Imgur: The magic of the Internet
Imgur: The magic of the Internet
Imgur: The magic of the Internet

1) I checked with my multi metter (photod), it is showing that the fuse is good.

2. I do not have the 6.35mm jack or adapter, I can test to see if I get anything with my scope

3) I tried all the inputs and radio iirc, but will double check

4) Are the speaker feeds the mosfets responsible for controlling the power to the left and right channels?

Thanks Mooly

Last edited by 22asd; 20th September 2019 at 12:07 AM. Reason: IMGs were not posting.. changed just to the link to the image on imgur. Thank you
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Old 20th September 2019, 06:53 AM   #4
Mooly is offline Mooly  United Kingdom
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Denon DRA-300 Dead Left Channel
Are the output transistors FET's? What are the device numbers?

You could compare the DC voltages on those four transistors as measured from ground. Each pair should be similar. Be careful when measuring not to slip with the probe.

Any major difference would indicate a problem and typically we would be looking for a high DC voltage of either polarity on the pins that feed the speakers. Depending on the circuit configuration that could be either the Source or the Drain pins.

You should see supply voltage on whichever pins (Source or Drain) do not connect to the speaker output.

The most common configuration would have supply applied to the Drains, positive supply on the N channel FET Drain and negative on the P channel FET.

You can also scope the FET's and see if audio is present.
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Old 20th September 2019, 10:49 PM   #5
22asd is offline 22asd  United States
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Quote:
Originally Posted by Mooly View Post
Are the output transistors FET's? What are the device numbers?

Here is a better pic: imgur.com/kjymNN5



Two of the transistors on the outside TR319 & T320: WingShing C2577

datasheet screenshot of C2577: imgur.com/l8Aq8H8


The other two in the middle, I am not sure. The company is WingShing also.



I will test them shortly and report back!
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Old 21st September 2019, 06:49 AM   #6
Mooly is offline Mooly  United Kingdom
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Denon DRA-300 Dead Left Channel
Try attaching your pictures directly

How to attach images to your posts.

C2577 are actually 2SC2577

2SC2577

And if all the outputs are the same type (no 2SA devices pairing them) then the output stage is a more unusual quasi complementary type.
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Old 22nd September 2019, 01:39 AM   #7
22asd is offline 22asd  United States
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Quote:
Originally Posted by Mooly View Post
Try attaching your pictures directly
Roger that!


I tested the 2SC2577 and the 2SA1102, they all seemed fine and were operating relatively within range of each other. There were no obvious signs that they were not working or there was a short



I tested the voltage on the headphone jack with the multimeter and they were both similar and the voltage was jumping around from .6 - 1.1 volts


side question: is the difference between the bipolar and fet transistors that one amplifies power while the other (fet) bucks the power?
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Old 22nd September 2019, 06:55 AM   #8
Mooly is offline Mooly  United Kingdom
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Denon DRA-300 Dead Left Channel
In very simple terms bipolar transistors are 'current driven' and require a flow of current into (or out of depending whether NPN or PNP) the base in order to conduct.

FET's are voltage driven and at DC essentially draw no current into their 'Gate' from the stage driving them. At AC the driving stage has to supply enough current to charge and discharge the Gate capacitance.

Transistors have current gain. If 10 milliamps injected into the base causes a collector current of 500 milliamps to flow then the transistor has a basic current gain of 50.

The gain of a FET is expressed differently and this is called 'Transconductance' and that is a measure of the change of current flowing between Source and Drain of the device versus the change in voltage applied to the device (applied to the Gate).

We really need to see a circuit of the power amp to advise better what you should be seeing although the output of the amp should certainly be very close to zero volts at all times.
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Old 23rd September 2019, 05:44 AM   #9
22asd is offline 22asd  United States
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Quote:
Originally Posted by Mooly View Post
We really need to see a circuit of the power amp to advise better what you should be seeing although the output of the amp should certainly be very close to zero volts at all times.

I posted the images like you said but I had to down the quality 50% to post them here. This is a link to the original photos in one gallery JIC: Imgur: The magic of the Internet



I will record the measurements on the 4 output transistors and report back. I do not believe I was getting 0 volts on the emitter leg.
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Old 23rd September 2019, 09:21 PM   #10
22asd is offline 22asd  United States
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Values are +- respectively. I tested voltage with a 1000 Hz w sine wave loop from youtube

2SC2577: B= 1.27v, C= 42.6v, E= 1.09v

2SA1102: B= 0.89v, C= 42.9v, E= 1.075v

I also noticed that the left hand resistor (R347), the silkscreen print is faded while the other is very clean and legible. I know it doesnt necessarily mean it is bad, but it could be. I have never seen a three leg resistor before except for a variable resistor. Never knew these existed, should I test them? If so, how?
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Last edited by 22asd; 23rd September 2019 at 09:32 PM.
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