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Hello folks! I could use your help with Donkey Kong Jr., please!

The Issue:
My copy of Donkey Kong Jr. seems to be suffering from frequent, intermittent audio drop-outs, making it sound scratchy/crackly/static-y.

Example:
I have uploaded a clip of the intro (with sound) that you can hear here: You can see a visualization of this issue in the audio spectrogram in the provided image attachments on this post.

Work Done:
  • Recap - no effect.
  • Replaced chip at 7K with new LM324 - no effect.
  • 8035 sound processor removed, cleaned, resocketed - no effect.
  • Chip 3H (sound files) removed, cleaned, resocketed - no effect.
  • Nintendo to JAMMA adapter swapped for a different design to ensure audio amp not at fault - no effect.
  • Verified unit is receiving appropriate voltage.
Work to be Done:
  • Replace DAC-08
Details:

First it's probably important to identify that I am an amateur and still learning. I can not fluently read a schematic, but I am resourceful and picking it up as best as I can.

Second, it's also probably important to identify that this unit is not in a cabinet. None of my games have cabs at the moment due to space restrictions. I play them using a Supergun. Specifically, the setup is a Mean Well RT-85A switching power supply, an RGB's Lab HAS v5 supergun with JAMMA extension, and an OSSC Pro.

The audio issue at hand can be seen demonstrated visually in the spectrogram image attached to this post. The audio frequently, but briefly, cuts out. This causes the audio to sound bad, stuttering/crunching. Insofar as the music and sound effects are concerned, they seem to play correctly, it's just cutting out.

I attempted to look up the schematic information in my operators manual, which identifies that it's for the "DJR1-UP" model, "2 P.C. BOARDS TYPE." When reviewing the schematic drawing, though, I noticed that the alpha-numeric sector designations do not match my own board's layout. I do in fact have the 2-board type, but given my inexperience with schematics at large, I'm unsure if the mismatch is actually indicative of me having the wrong manual or not. I also took to the internet, where I found minimal resources. This is all a long form way of identifying that I'm unsure what constitutes the "digital audio" circuit on the board, so I am not 100% sure on where to look beyond the areas I've already messed around with.

With all that in mind, according to the sources I found it seems the chip on spot 7K is often the source of audio troubles. From the resources I found, it was suggested to replace this with an LM324 chip. So, I replaced the chip, and did not observe an improvement.

I then removed and cleaned the MBL8035N 8216 C55 audio CPU in spot 7H. I cleaned the pins with a fiberglass scratch pen, and flushed the socket with DeoxIT fluid before resocketing it. This yielded no improvement.

I then removed the chip at spot 3H (which contains the audio data) on the board, cleaning the pins with a fiberglass scratch pen, and flushing the socket with DeoxIT fluid before resocketing. As with the audio CPU, this yielded no improvement.

I then thought that it may be a result of the amp circuit on the Nintendo-to-JAMMA edge adapter I was using. To rule that out, I purchased a different one which utilizes a different setup. This did not yield an improvement, and the same audio issue was present.

I have also completed a recap of the electrolytic capacitors on the board, as part of routine preventative maintenance that I intended to complete anyways. This, too, yielded no improvement.

If anyone has any information that could help me to resolve this, I would greatly appreciate it. If you happen to be familiar with the digital audio circuit for DK Jr. and know of some troublesome areas that I can investigate? Really, any signposting would be great here- I just need to know where to look.

Thanks for your time!
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