As a side note, potentially related -

The 'original' 7-digit ROM (unversioned number) used a hacked way of handling the additional digit. This caused the display routine to suck up a lot more cycles than was necessary. (The v24 version is based off of Stern's 7-digit OS.) But - because of the different times needed in the display interrupt (which happens quite often), this will cause sounds and speed of the game to be noticeably different. I didn't notice it affect gameplay, but it's possible that if the display interrupt timer is too quick (say, quicker than my MPU-200 was), it could start to cause other things to fail.

Oh, and the Bonus 255x issue was a RAM mapping error. The ROMs labeled 'Alt' on IPDB was Stern's fix for it. v24 does *NOT* have this fix in it.

Dumb question, but the 4x MASK vs 2x EPROMS, could it be a voltage issue?
Could the additional load on one or any of the lines be preventing an address or data line from getting high enough (current draw) for the NVRAM to see it, but is high enough for the SRAM to recognize it as a HIGH?

I have been holding off saying anything, because I know that sometimes 'noise' can be bad and help get away from the real issue, but I thought I'd share something -

I was running v24 (the 7-digit OS) for over a year now. On original hardware (do not know if my MPU had that trace fix or not) - without any issues. No sound issues at all.

Then, at some point back in this past December or January, it started showing the sound issue. I went ahead and rebuilt my SB-300. A LOT of chips for replaced (almost all of them, except for the timer), and caps all got replaced. This did NOT fix the issue.

Then I went ahead and got @barakandl 's MPU board. (For two reasons - to have a good 'test' board to swap out if needed, and to see if it helped with this.) Setting the DIPs to the v24 on IT (not sure if code was identical), the issue did NOT go away.

I have NOT replaced the timer on my SB-300 yet. That is next.

However! Here's something interesting. Back in May, had guests over, and was playing multi-player games. Everything seemed to be fine - except for the audio. A couple weeks after they left, I turn the game on, and notice that my HSTD is .. corrupted. Displays read "5<space>438". I have yet to reset the board, but.. thought I'd mention it in case it was important.

Also - at some point between the start of v24 and now, I replaced the sound cable. My **original** cable was ALL pins. The replacement I got was only 32 pins. (Hey, @barakandl - remember I mentioned a long time ago to make a second adapter for the audio cable, allowing it to use a ribbon cable? So in case new sound boards are released, it'd be easier to hooke them up? And you said 'nnaaah' .. and now you made a sound board, even, and STILL can't use a ribbon cable. )

Eh, i was just being a dick. I'm not actually upset. I DO (and have) wondered hot 'iffy' connections could affect the soundboard, though.)

Haven't unplugged anything while the game's been up. Been solid, save for the sound!

Ah, awesome! Thank YOU!
I have the source for v24, and would like to add it in. Or have it added in to that version, if we can work that out!

Sorry, I was referring to this part, here:

Could we get it added to the v24 ROM? (Either sending me the code you have, or I send you the source for v24..)

Ah, okay then! I can look into it. It's be nice if the true 7-digit fix could fix it itself like the Factory Fix one does - by wiping the needed areas. I'll look into it then. (I have NO trouble burnig ROMs - however, since I'm working on adding some small features to v24, I'd rather just nip it in the bud and prevent me from having to swap out ROMS because of some bad code of mine.)

Well, update on my machine -
The pinball gods hate me, sadly.

Reset NVRAM using the ROM above - turned game on, went through audits and reset everything. Played game, still had sound issues. I thought, 'Hey, maybe one of the new audits in the v24 is affecting it!' So I put the RAM clear ROM back in, power game up. Got static out of the sound board, and lights would randomly flicker. Took ROM out, checked to make sure (idiot me) didn't bend a pin - nope. Reinsert ROM, this time get the expected flash. Remove ROM, turn game back on and play withOUT resetting audits. Still messed up sound.

Next step for me? Replacing the chip on the sound board.

(1) - Yes, that is correct - the background noise is wrong, the spinner silences everything, and other (seemingly) random noises are cut off or distorted. (Like the explosion.)
(2) - No, everything got reset to either "blank" or "0000". In this state, I CAN play a game - no display in the credits window, but it'll start games. After manually resetting all audits to "00", then I have to add credits before starting.

I'm not TOO worried - at least, not until I get a new timer chip for the soundboard. It's been completely rebuilt, including bypass caps (and audio caps), and there's only two chips that have NOT been replaced on it.

Ah, good point! No wonder you get paid the big bucks. I didn't think of this; will give it a try tonight.

Well, this is interesting.

So, the board is pfutzed - SLIGHTLY. I'm missing some bass cap or a chip I replaced is bad - my bonus countdown is just 'wrong' (hard to explain), and some of the sounds sound different. This does not affect below.

That's not the interesting thing, though -
Booted up to the alt/fix. Everything sounded pretty normal. Had to reset all audits after changing. Peachy.
Played a couple games. Then booted back up into the 7-Digit ROM.
Sounds were PRETTY CLOSE to being on-point. The spinner sound played, but it seemed as if it was getting cut short. ALL other sounds (save for what I say above) sounded correct.

So I will stop my testing there for now, until I either go over my audio board again (or just get a new one). The rest of it can wait on my machine.

Yup, I'm not touching a thing - I'm putting U2 in (27C64), removing the jumper, turning on. Almost immediately (under a second) LED blinks a little faster than once/second. Turn game off, remove ROM, replace jumper, turn game back on. Will do it again tonight and grab a pic of the displays.

(Also, since it's working for other folks, I'm not blaming the MPU or the ROM. I seriously am some kind of Bermuda Triangle when it comes to //odd// issues with games.)

Use the 'Alternate' ROM on IPDB for the bonus bug, 6-digit.
The "7-digit bootleg" does not have the bonus bog, and runs slower due to how the 7th digit was implemented.
The "v24" version supports 7-digit natively, but has the bonus bug and COULD mess up sounds on your game.

Eventually, the v24 version will be fixed to correct the sound issue and bonus bug.

Has it? I don't have a copy, and I thought I had the last one. Can you forward it please?
Also, is it still v24? I would forward it to barakandl so he can update his MPU.

Pffft, dick. After I gave you some help, and then you tell me you're no longer gonna work on it, now you come out and say this? I'm hurt. You have it posted somewhere so I can find more issues with it?

Mind forwarding v26? Because of issues with Jay and IPDB, it will likely be a while before it's posted. (It's not up there now, and depending on when you sent it, it could be a while before it is posted up there.

I HAVE noticed this - BUT - my SB300 is also really old and seriously hacked. (No, I don't have a new replacement yet!) Up until we found that the RAM has to be zeroed out, I figured all MY issues were just coming from a bad board. (In fact, I'm still having other issues that IS because of the board still, so.. I put very little thought that my_ issues are because of things outside the sound board. Heh.)

Understood though - if you want a tester (like on v24 last year), lemme know. Be glad to do some testing on OEM and barakandl 's MPU.

Didn't even realize people were complaining about that. Interesting. Guess I need to start popping and catching up on RGP again. In either case, awesome. Good to hear then.

*snrk* Glad I didn't miss much then. Heh.