Donkey Kong Jr. Audio Dropout/Stutter

DillingerRadio

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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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I'm not sure that piggybacking an analog amplifier chip is an effective way to test it. That method works with RAM or other digital logic, as long as the chips aren't fighting each other. Since I'm hearing distortion with both digital and analog audio in your recording, replacing that amp would be my first suggestion. I believe the joke regarding the LM324 is that they named it that way because you should buy 3 to 4 replacements for it each time you think you need one.

Edited to add: How do your power supply outputs look?
 
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Did you recap the small audio amplifier PCB mounted on the monitor assembly?? If that board has never been recapped, that could likely be your issue.
 
You've got questions, I've got answers.

@RiddledTV - Ha! OK! I will pull that chip (7K) off and properly fit in a replacement LM324 (or two or three) just to triply check. Thank you for the insight! With regards to power, 5V at the edge. I have an adjustable RT-85A that I use in conjunction with the HAS unit's JAMMA extension. At the edge side of the extension is a voltmeter and I confirmed it to be accurate with my multimeter.

@yaryar - Thank you for troubleshooting! I don't think that's quite the problem in this case as I use a Supergun and not the original cabinet (I just updated the post to include that information, my bad). That's super useful information though, and I appreciate you throwing in a place to look!
 
LM324 uses -5V power as well. Those Nintendo boards pull a lot of current from -5v, so if it's cutting out... It might explain what you're hearing.
 
Aye, I believe the Mean Well RT-85A is well suited for it (and all my other games). It provides 5 V @ 8 A, 12 V @ 3.5 A and -5 V at 0.5 A. The 5 V rail is adjustable, so what I do is dial it in to 5 V unattached, then attach the board (power off, of course) and dial the power in again after checking the draw to ensure it hits and maintains 5 V.

I'll see about getting that chip at 7K off and report back once it's done - thanks again for everyone who's contributing/viewing/etc. I appreciate it.
 
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OK! I went ahead and desoldered and replaced the chip at 7K with an LM324. While I was doing that I also reflowed the DAC, since it sits right next to it.

Results:
  • Mixed.
    • On the first: this has dramatically improved the quality. It still has the occasional hiccup but is otherwise satisfactory.
    • On the second: no effect. The audio continues to sputter, unfortunately. I will replace the DAC next, just to rule it out.
Lessons Learned:
  • Piggybacking a chip is OK in some circumstances, but probably should not have been trusted in this particular case. Given the relative ease of removing the chips, I should've just done the work.

I have updated the original post, and will provide another update after I have removed and replaced the DAC on the unit which is still experiencing issues.
 
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I hate to be so stubborn, but I still feel like you should actually confirm that your -5V power is keeping up. The ECL chips on that boardset use a LOT of -5V power, and they produce a lot of heat.
 
No problem at all. I think that's an entirely reasonable suggestion. I am happy to go ahead and measure it.

I placed the harness back on the unit and powered it on once more. Checking the Nintendo side of the Nintendo-to-JAMMA adapter, I measured the negative voltage off pin 6. You were correct that -5 V was slightly undervolted. I actually had to overtune the power supply to 5.2 V on the harness edge to drive -5 V on the Nintendo side. However, the adjustment does not appear to have improved the situation, and it retains the same audio behavior (and now everything on the positive side is slightly overdriven). While the power overall needed a slight increase to meet -5 V, it was steady throughout and didn't exhibit any fluctuation.

This is a recording of it after having installed the LM324 and adjusted the voltage to drive a full -5 V at the edge:
 
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So you have 2 different complete DKJr boardsets that are both behaving similarly with the same bad audio. The only commonalities are supergun, Nintendo to jamma adapter, and power supply?

From a probability standpoint, the chance of 2 different boardsets having the same fault is unlikely. It seems like I'd try find a way to test those boards in another cabinet.
 
Yeah. I hear where you're coming from definitely. Unfortunately, I don't have access to a cab, and am unlikely to gain access to one any time soon. I live in a rural area (so, no local resources), and I don't have the space for a cab in my home. While I can't rule out that it may be a problem with my Supergun setup, this setup has worked flawlessly with a number of other arcade games besides Donkey Kong Jr. Including other vintage titles like Ghosts 'n' Goblins, Double Dragon, etc. :unsure:

The two units have a similar problem presentation, but their root causes may be different. I thought the LM324 replacement had actually succeeded with the first unit, but the gains- whether perceived or actual- seem to have since been lost. The second unit did not seem to improve at all when I installed a new LM324. Perhaps I'll do some logic tests to compare against your results (thank you for providing that resource) and see if anything stands out.
 
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If you are gonna use a meanwell supply consider the RT-125A. Nintendo boards need a strong -5V rail due to the ECL shinanigins.

Regarding piggybacking LM324s. I have lots of success piggybacking them, they won't solve all the issues but the point is to see if you get any improvement.
 
Thanks for your input folks. It's sounding like the power has the potential to be an issue.

That's something I can act on relatively easily. I've ordered an RT-125A. It should take a few days to get here, and I will update this post when it does!
 
Hello again, everyone!

I apologize for the long delay on the update. I mistakenly ordered an RD-125A because it snuck in amidst the listings for an RT-125A and I did not notice. After correcting my order and receiving the RT-125A, I immediately set about testing if the power was the problem.

It was not.

You may see a video of the issue here (powered by the new supply, which provides the -5V at 1A as previously discussed):
As you can see, it performs the same as it did with the RT-85A. Sound continues to be a problem, with more of the same snap, crackle, and pop. If anyone has any further ideas where to poke or prod that might be causing these artifacts, I'm all ears. :geek:(y)
 
Does adjusting the volume on the Jamma adapter make it any better or worse?
 
Does adjusting the volume on the Jamma adapter make it any better or worse?
Good question, and something for which I tested after the power supply impact was negligible. Unfortunately, it does not really impact the sound quality at all. I've also used an entirely different adapter and it yields the same audio issue, despite having a different amp design.

Something I've noticed is that this seems to be a somewhat transient issue. Sometimes (very infrequently) the sound works well enough to fool me into thinking things are resolved (at least enough for me to be satisfied,) only for it to then sound poor the next time it gets booted up. :unsure:
 
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