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To begin, I have very minor knowledge of electronics and circuitry. I can read a schematic and have basic knowledge of transistors, capacitors, etc. However the extent of my repair experience has been cleaning circuit boards in a couple devices and recapping a couple speakers. That said:
My Denon DRA-1025R is in need of help. After playing for 15 -20 minutes the left channel begins to fade. Eventually it takes 2 to 3 notches left on the balance to keep balanced sound.
After considerable time searching the web and going over schematics / wiring diagrams I have come to the conclusion that the problem most likely lies specifically in the left channel section of the amplifier board. And that the most likely culprit would be a capacitor or capacitors.
At that point I am stumped. Are there any guide lines as to where to start? Does one just begin pulling capacitors out, checking them and replacing until a malfunctioning one is found? Or is there a logical test sequence that will indicate a beginning point. Finally, since the left channel is going, is there a good chance the right channel is on the brink? And if so, would it be a good idea to just replace components on both as a precaution?
Thanks in advance for your advice.
Ron
Follow Ups:
Nothing beats a Schematic, VOM, an Oscilloscope and a Test CD with tones (or Audio Signal Generator).
To me it sounds like your amp has developed a fault inside of a switching IC or has a faulty Transistor in one channel or a faulty Amplifier Output Module.
Brute force parts replacement can be tedious and frustrating.
Make sure that your RCA interconnecting cables are all good.
A weak channel that becomes weak after a period of time sounds like an IC, Transistor or Module.
Faulty Capacitors will often exhibit their problems at power up, not after warmup, but this may not always be true for Power Supply filter caps.
I have repaired many Solid State Integrated Amps and I have found that there are channel input switching IC's that develop problems and cause one channel to sound better than the other.
Without a Schematic and some test equipment, you may be able to work it out after a long period of trial and error.
My tried and true is the following:
Get a copy the schematic.
Measure all of the DC voltages, compare to the expected values.
Once the DC voltages are all OK then start to trace a signal through from the input to the output with an Oscilloscope.
Faulty DC voltage could indicate a Regulator IC issue.
Eventually you can reach a point in the circuit where the signal looks the same for the Right and Left Channel, but when it exits the component on it's way to the next Gain Stage, you will see that one side is lower than the other.
This is the part of the circuit where the signal is being attenuated or distorted.
A final possibility are cold solder joints or even dry solder joints.
You can try and reheat suspect solder joints.
To look for a dry solder connection I usually use a 100 Watt lamp and place it under the PC board. I look at the other side of the PC board for bright white light specks, these can indicate a solder connection that was missed and needs to be soldered.
There are many other things that can go wrong such as flexible ribbon cable connections and loose wires.
Best of luck and happy Asylum Hi-Fi'ing.
The bitterness of poor quality remains long after the sweetness of low price is forgotten
I have everything except the oscilloscope. Freeze spray has been ordered, and I'll that first along with checking connections, looking for loose wires, etc. If nothing is found you may see this on EBay as "used, left channel fades."
Although, for the price of another used receiver that may have problems this could probably be professionally repaired.
Decisions, desicions.
You may be able to find it with freeze spray. Let the channel fade, then spray components one at a time, that is very little spray and you can isolate adjacent components with cardboard or anything you have on hand. Small amount of spray on the problem component and volume will come back.
nt
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