[SOLVED] - Audio Issue on Donkey Kong 2 - Distortion on lower frequencies

johnczerwinski

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Need some direction on where distortion is coming from on a Donkey Kong 2 that I'm working on for someone (not my game)

Symptom:
Higher frequency sounds seem ok, but when there are lower frequency sounds (ex when the monkey stops he's feet) it sounds a bit crackly / distorted (see video below).

Background
He bought the game and the sound was VERY soft...almost couldn't hear it. Looking through the audio amp on the Sanyo 20-EZ, I noticed someone tried refurbishing it and accidently switched the power transistors (PNP swapped with the NPN and vice versa).
I went ahead and put in new transistors and e-caps (the right way) and the sound volume is great, but the lower frequency sounds get a little distorted. I don't know if this was like that before someone tried fixing it, or the amp is still the problem, or the PCB has an issue, or the speaker etc. He said it's a new speaker.

Resolution:
It was the audio amp, specifically R383 (39 Ohm fusible resistor).

 
Last edited:
It's hard to tell from your videos, but I do hear the distortion from the stomp sound. Does it happen with any other sounds?

The most time-saving diagnostic tip I can offer is to try a different nintendo game board in that cabinet. Or likewise, swap in a different audio amp from another Sanyo 20 EZ and see if you can isolate the problem to the DK game board, or the audio amp. My money is on the audio amp.

1738429771275.png

I can't decide what would likely die if those highlighted transistors were swapped.

If it is only occurs during the stomp sound, on a 2board DK, there is a 556 @8N and a 4049 @8L where I would investigate the inputs and outputs. I'm not sure what locations those translate to on a 4-board PCB.

best of luck!
 
It's hard to tell from your videos, but I do hear the distortion from the stomp sound. Does it happen with any other sounds?

The most time-saving diagnostic tip I can offer is to try a different nintendo game board in that cabinet. Or likewise, swap in a different audio amp from another Sanyo 20 EZ and see if you can isolate the problem to the DK game board, or the audio amp. My money is on the audio amp.

View attachment 796993

I can't decide what would likely die if those highlighted transistors were swapped.

If it is only occurs during the stomp sound, on a 2board DK, there is a 556 @8N and a 4049 @8L where I would investigate the inputs and outputs. I'm not sure what locations those translate to on a 4-board PCB.

best of luck!

Thanks for the suggestions! Thinking the same with swapping out another board and amp (I'll need to scrounge one up). I'm wondering if the other transistors (the ones driving the base of the power transistors) are damaged or the diode. I'll check them too.
 
SOLVED: It was the audio amp, specifically R383 (39 Ohm fusible resistor).
 
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