AES Rev 3-6 - Loud Buzzing Audio, No Sync if Audio Cable Removed

[BurnKnuckle]

Hey guys, my friend has a problematic AES, Rev 3-6. I'm usually good at identifying mistakes
or damage, but I am stuck on this one, and I would appreciate any help with diagnosing.

Image Gallery of AES PCB

Some points about this console:

• Neo Geo AES console, Revision 3-6 Board
• Using an Insurrection Industries RGB SCART Cable
  - Audio cable taps from headphone jack and mixes into cable just after DIN out
  - Cable is wired for C-Sync
• Full electrolytic re-cap, polarity & values checked out
• RGB Bypass mod
• Basic, no-frills RGB SCART cable was used recently

The Problem: Loud Buzzing Audio, No Sync if Audio Cable Removed

• The video output is excellent (better than stock because of bypass mod)
• Headphone audio out is completely buzzing,
  - Sounds like another signal were there instead of audio
  - Can not hear any other audio from game except buzzing
• If audio cable is detached:
  - No sound (obviously)
  - Video loses sync completely
• Can't use Mono Audio out from DIN because bypass mod edit 7/12/2021~2:30PM EST
• With an OEM AV Cable, a TV didn't pick up audio because Composite Out is cut (due to bypass mod)
• The basic SCART was just tested (which doesn't mix headphone jack) and mono audio from DIN out is confirmed all buzzing. end edit
• Note the Red-Orange Jumper wire on the back of the board
  - If jumper is taken off, and cartridge in, you will see that screen on the last picture.
• Basic RGB SCART cable when tested:
  - Sync is good
  - No audio

Note: Even before the RGB Bypass and Re-cap, issue was there. Was not remedied with these two jobs.

I've included the gallery of high-res pics up above.
If anyone has seen something like this before, please give me a clue on what to look for. Thank you!

 

[Neo Alec]

I assume you plugged headphones in the jack and it's just buzzing? No video when the audio cable is removed makes it sound like the scart cable is relying on the headphone jack for the ground connection, rather than ground from the multi out DIN.

Why did the RGB bypass mod remove mono audio? Isn't the lack of audio just because your scart cable is designed to take audio from the headphone jack instead?

 

[GohanX]

It sounds like you have a grounding issue, but whether it's the cable or the system I can't say. The cable shouldn't be relying on the headphone jack as its only ground, and Insurrection Industries stuff is generally pretty good so I'd probably be looking at the system first.

 

[BurnKnuckle]

First of all, thank you for the responses!

headphones in the jack and it's just buzzing?

Yes, confirmed buzzing audio solely on headphone test.

No video when the audio cable is removed

There is video, it's just once audio jack is pulled, image immediately becomes wildly out of sync, as if ground were removed or interfered by something else.

RGB bypass mod remove mono audio

My bad, I meant to elaborate on that one later and forgot to fix it.

Using an OEM AV Cable, the TV didn't pick up on the audio because the composite was cut (due to the mod)
The basic SCART was just tested again (doesn't use headphone jack) and mono audio from DIN out is confirmed buzzfest.

whether it's the cable or the system I can't say

Tested the Insurrection SCART cable on a known good AES (Rev NEO-AES) and all is well on that one.
Good RGB Video & strong, clear stereo out from headphone jack. No sync issues.


At this point, I believe we can eliminate either cable from being faulty, and looks to be somewhere on the board.
Let me know if any more pics are needed. I will update the original post.

 

[Xian Xi]

Who did the mod?