Can you post a picture of your CPU board?

Have you tried reseating the 6802 at U24 on the CPU board?

I have spare working sounds boards if you determine that is the issue.

May want to go over the IC pins with a pink pencil eraser if it acts up again. But be careful not to put too much pressure on the legs and bend them.

I had found quite a few bad Hitachi 6802 (that brand you have in U24 now) fail. Hopefully, this is not one of those such times.

Background music and the "bong" are generated on the remote sound board, not the CPU sound section, however the commands to that sound board originate from the PIA on the CPU board that is just below the battery holder. That PIA is controlled by the main processor, not the speech/sound processor at U24. If there are corroded traces this could cause some of the sounds from the background music board to not initiate or possibly initiate the wrong sounds. However that shouldn't cause the background sound board to reboot (the bong is the board booting up) and hanging on a note is likely that board locking up.

Inspect the small ribbon cable and the are on the CPU around the battery holder from the PIA to the cable. Reseat that ribbon cable at both ends and reseat all the connectors on the background sound board. Reseat any socketed chips on the background music board.

So typically on most pinball sound boards that generate music the following happens when it experiences a reboot. The command to play music only occurs once. Usually at the start of a ball or when the game changes states, i.e. ball in play to end of ball or after locking a ball or starting a new mode or starting multi-ball. So if the sound board reboots mid-game, it will make the boot-up sound (a bong for Williams games, a short speech quip on DE games). The board will continue to receive new sound cues so it will continue to talk or make sound effects, but the music will not restart until a change in state happens, i.e. end of ball or start of multi-ball.
You can see this on some (most?) system 11 games if you quickly press the start button when powering on the game. If you start the game prior to hearing the sound board boot-up bong, the sound board will have missed the start music cue and will then play most of ball 1 without any music. once you drain the ball the music starts on ball 2.

As PinballManiac40 said those Hitachi CPU chips (and Hitachi 6821 PIA's) tend to fail more frequently than the Motorola. Just note that if you change from the Hitachi 6802 to the Motorola 6802 I believe you have to change a jumper on the CPU board.

you can also swap the sound board ribbon cable around end to end and see if it persists.

Seen a bad ribbon cable cause this exact issue . Do as Kbliznick says and reseat socketed chips like the eproms etc. Plus reseating the cable many times may help as it cleans the terminals off the more you do it.
Never hurts to get a new ribbon cable though. Cheap way to make sure its not the problem. You should inspect the pins on the boards too. Seen the odd pin missing before and some not making connection due to poor factory solders.

Could this be a 5v issue coming from
Ps?

Better to get a new ribbon cable. Reseating the cable also wears and stretches out the female sockets of the connector, which can make a poor connection just worse. These are not meant to be plugged and unplugged repeatedly. http://www.pinrepair.com/connect/#worn

yes thats why I said to get a new cable if reseating helps. Its always best to replace it. they are cheap.

if problem persists check your continuance between the board connector pins for the ribbon cable and the legs of the 6821 pia that controls the sound data - iirc there a RN in-between the two, if thats all good, then plug in the ribbon cable and ring it out, but sounds like dirty pins or worn out ribbon

I had a very similar problem on my Pinbot. My issue ended up being low (high?) -12v coming from the power supply. It was -10v but it needs to be at least -10.5v or it can cause resets, and seems to particularly affect the sound board. This can be tested on the three test points in the center of the power board, left -12, center ground, right +12v.

What solved it was replacing the capacitors on the power supply as they were original and had dried out.

Just checked my Pinbot Manual and I had it backwards, it’s + not -:

Unregulated +12v on the power supply, TP3, should not go lower than +10.5 or resets will occur.

Had same problem on pinbot board.... it was the eproms. They verified good, but I burned a set anyway after doing much of what you've been doing, and that fixed it. As a test a couple weeks later swapped the suspect set back in (to make sure it wasn't something goofy with the IC sockets) and sure enough, issue came back.

I have this exact problem with my Bad Cats machine. Background sound doesn't come back until the start of the next ball. When it drops out I don't hear a bong though, but I've suspected that it may be losing power or something. I'm going to replace all connectors in and out of the power supply here real soon too. I will check the +/12 voltages as well.

This is what I've done so far (for various reasons): I've replaced the MPU with Rottendog (until DumbAss board is ready) and put in new 6802 processors, replaced original sound board with Kohout sound board, replaced power supply with Kohout one, replaced audio ribbon cable between MPU and sound board, replaced all connectors in and out of the sound board, has new speakers, has all new ROMs in MPU and sound board. I programmed the ones for the MPU; the new sound board from Kohout came with the ROMs.

Which ROMs did you replace?

Edit: Getting +12 and ~ -13.3 or -13.4. Varies a bit. Cause for concern? Could sound board reset if voltage is too low, I guess in this case since it’s a negative voltage?

Edit 2: Burned a whole new set of ROMs (I didn't mess with the ones that came with the sound board, yet anyways) and switched the processors around and still am getting the same results; background sounds drop out randomly and then come back at the start of the next ball, or in the case of the last time, it was on Ball 3 and came back at the start of the next game. I did check the ROMs on the sound board and they did verify Ok. Any other ideas?

The one on the sound board. Verified great, but just didn't work after it dropped out.

What Bad Cats main version do you all have? Is it the latest?

Ok. I will burn a new set for the sound board; maybe there’s an issue with the ones from Kohout/PinballPCB. Game ROM is L-5, which is latest I believe. All others are L-1.

Damn, just happened again with the ROMs I burned.

Sheeesh that’s crazy you are still having the issue after all the fixes and upgrades you’ve done. My machine sometimes does nearly the same thing as you described, however, it will have all sound, but no music. But when the next ball starts, the music starts. It doesn’t do this often, and it is usually immediately after powering up the machine and starting the initial game.

You are pushing the start button before the sound board has booted and gives it 'bong' tone.

Come on man give me some credit of course I don’t do this lol.
Here is my game room start up drill: turn on black light, manually power up 6 pinball machines, start 3 arcade machines, then play whatever I’m in the mood for. Sometimes Pinbot will have been on for quite sometime before I get around to playing a game (if I even do). I don’t just roll in there and turn on one game and immediately hit start.

Occasionally when I power the machine up, it will lock up when booting, and the “bong” tone will be in a constant loop.

It is good. That is an unregulated 12 volts so it will vary.

Just one idea. With the game off, turn the volume pot up/down 10 times and try it again.

What are 5v, 12v and -12 volts measuring on the power supply?. This is an original power supply board? Mind posting a picture of it?

Have you reseated your ribbon cable between the MPU and sound board?

So you have an original Williams MPU installed? If so, mind posting a picture of it?

Have new volume pot on sound board.

New Kohout power supply. Voltages taken directly off of the board. Yes I’ve reseated all cables and connectors multiple times.

Some pictures here: https://www.dropbox.com/scl/fo/d9ewdsb60zqy09db7d0gg/h?dl=0&rlkey=hvoak7ay6z3xd7nm6bcuryhqw

Just a tidbit of information, reseating only sometimes works in the case of a little oxidation or dirt on the male/female pin connections. In many other cases, it is actually working against you. These cables are only rated for so many "cycles" (unplugging and plugging back in) and have a spring tension of contact points. Over time, these can simply weaken and loose their gas tight seal. When that happens no amount of reseating fixes the cable, and possibly makes it worse. The only fix is to replace the cable. More information than you could ever care to know is here, and worth a read:
http://www.pinrepair.com/connect/

There is not a volume control a system 11 A or B original sound board that I am aware of. Edit: I see pictures of your Bad Cats in the link and you have an aftermarket sound board. Never seen that one before, but I would not expect an issue with that sound board.

I would be talking about a volume control inside the cabinet. Turn it both ways 10 times while power is off.

Rottendog MPU boards are notorious for different sound issues mostly because of design issues, so likely issue is cause of it.

What is wrong with your original MPU board?

I really suggest creating a new repair thread. This thread was created by the OP for his specific game. You have a unique situation that does not involve even the original Williams boards anymore. Makes things more complicated.

First, I agree about starting a new thread. My suspicion is that your new sound board could have issues... either defective or unknown/incompatible issues.

If it was my game, I would replace the old caps on your old sound board, then re-install it in the game and test that setup carefully notating any changes/symptoms to help rule out any odd, one off sound board issues. If they BOTH act EXACTLY the same after replacing caps on the old sound board, you then have a little more evidence that this is NOT a sound board issue.

I am assuming you replaced the old sound board (thinking it was causing the problem) and it may have just needed new electrolytic caps or, it may have been completely fine all along.

Right, I am aware. I “reseated” just in the normal course of taking the board in and out while working on it.

I got the new pot that plugs directly into the sound board just to eliminate the issue being with the original pot, which I didn’t think it would be, but why not when you’re replacing the board too. Original MPU had massive alkaline damage. Long story, but I no longer have the original MPU or sound board. Yeah I agree, I can start a new thread. I originally posted it here because I have the literal exact same issue as the OP.

I unfortunately do not have the original sound board anymore and I don’t think it’s the new one. I suspect it may be a bad PIA on the Rottendog, which is a loaner from a very generous Pinsider who’s letting me use it until my new board from DumbAss is ready.

Does not sound like the same issue to me. Seems far from it.

Background sound randomly dropping out while sound effects continue to work and all sound returns on the next ball on a System 11 machine doesn’t sound the same to you? That’s literally the exact same issue I have.

If so, then why is not yet repaired?

Same similar symptoms don't always equal same repair results