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Karaoke amp. Only right channel working

Rick79

Nov 26, 2014
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Pro karaoke DM-8200W
Nothing is getting hot and i dont see anything burnt or broken. I checked under the board of the channel that isnt working (Left channe) and i didnt see any cold solder or burnt marks.
I never worked on any stereo or amp that had only one channel working. Is there a quick way of narrowing down where the problem is?
 

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shrtrnd

Jan 15, 2010
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You've probaby got a circuit problem you're going to need a schematic for.
The first thing I'd do, is check your switches and potentiometers. If you've got a bad or dirty one, that might be the problem.
You wanted quick. That's what I'd do to eliminate the easy potential problems first. Then I'd worry about the amp electronics themselves.
(Also make sure your output connectors and speakers aren't the problem)
 

Harald Kapp

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  • Check the power supplies to the left and right channel.
  • Make sure the input signal is actually fed from the input connector to the PCB.
  • Follow the signal along its way through the different amplifying/filtering stages and note at which point it vanishes. You can use an oscilloscope or a test-amplifier with speaker for this.
 

canactech

Jul 7, 2009
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Check the voltage on each channel to be sure that the defective channel is completely powered. If not look for a fuse, on the board of the defective side like picofuse or even a resistor that could act as a fuse. It could even be a 1 ohm resistor. The second step is to chek for shorts on the amps fixed on the heat drain. Redo the welds even if they looks good,

Good work.

Canactech
 

shrtrnd

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YES! I forgot to mention that a lot of these amps have fuses in the speaker output circuit. Look for fuses on the board that lead to the speaker outputs.
 

Rick79

Nov 26, 2014
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Thanks for the replies! I dont see any picofuses but im gonna check the resistors and make sure the transistors are soldered good.
 

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Rick79

Nov 26, 2014
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Im not sure if this was done purposely or maybe they just installed the legs wrong, but if it was installed wrong, would that cause onther component to blow out?
 

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Harald Kapp

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It is unusal and definitely looks not like is was designed this way. However, there are a few transistors on the market with an unusual pinout. They may have designed with standard pinout but used another one for production, thus the bent pins.
 

Rick79

Nov 26, 2014
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It is unusal and definitely looks not like is was designed this way. However, there are a few transistors on the market with an unusual pinout. They may have designed with standard pinout but used another one for production, thus the bent pins.
It is unusal and definitely looks not like is was designed this way. However, there are a few transistors on the market with an unusual pinout. They may have designed with standard pinout but used another one for production, thus the bent pins.
The board for the right channel looks almost identical with the same original parts and that one component doesn't have the pins backwards. Should i try intstaling it correctly?
There has to be something wrong on this left channel board, but i cant figure it out.
I took a photo of the back of the amp where it says "EFFECTOR" it seems like the left and right channel boards gets their audio signal straight from the EFFECTORS input side. I took a photo of the blue and white wires coming from the EFFECTOR leading to the left channel board. And the other blue and white wire leads to the right channel board. I connected a set of RCAs to the output of the EFFECTOR to swap the left and right of the input to see if the left output has a signal, and it does, but whats weird is the left input jack is feeding the right channel board and the right input jack is feeding the left channel board. Is that normal?
 

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Harald Kapp

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What happens if you swap inputs AND outputs of teh two boards? If the defect is with the board for left channel, after swapping boards the defect should be in the right channel. This would at least narrow the search down to this particular board. If the defect stays the same, it is located anywhere else.
 

Rick79

Nov 26, 2014
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I have tried swapping the input and outputs and other ways, so far it has to be something on that left channel board. Without having a capacitor tester, or a schematic, i dont think im gonna be able to find the problem. I have the right side channel to compare readings to the left channel, but i still haven't found anything that reads differently.
 
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