No Sound S2000 very faint at 10

[qbert]

I am new to this forum so forgive me if I post in the wrong place etc. I own and repair quite a few 70s and 80s coin op video games but I'm new to slots.
I have read all of the issues on sound problems with S2K machines. I have two slots and I have been having sound issues with one of them.
The game has been playing fine for about a month. It has 504 rev A with the 47 ohm resistors on the input side to the audio amp located up top. (I find that if you just put the resistors on the left and right channel an leave the bottom speaker unmodified the bass notes are very impressive). About two days ago I started getting sounds like a microphone in the wind through the speakers intermittently when playing the machine, shortly there after no sound except I can hear it very faintly if I put the volume on 10 and place my ear to the speaker. It has multi media lite card and a 00042 simm card. Even if I disconnect the media board there is still no sound. I have swapped out the audio amp card up top and checked continuity from the plug located on the mother board and from the speakers to the audio amp. I even swapped power supply thinking it might be that. If I change the game entirely with a different 504 and mm I have sound so I believe I have narrowed it to the 504 board that has a problem. I am planning on changing out the LM1875T audio amp chip on the main 504 board.

 Has any ever had this type of issue?  Anything else I can check? What about the mother board could this be the problem?

Just for the record I had another game that also was in this cabinet and a similar issued occurred about 6 months ago. That stared with sound going out and required a game board change to fix. Is there something that might be causing the audio to fail on the boards?   

[Neonkiss]

Ya, Two boards shot with the resistor pack installed.
If I was you, I would remove those resistors and put the wiring back to normal.
Then buy a 504 revision B board and your done.

I may be the only one here that does not approve of the resistor repair for the 502 and 504 boards.  
and this is a prime example.

OH and WELCOME to the forum.
 
I'll give you your first K+ for a well research and thoughout question.

[Yoeddy1]

If you go with a stock 504B, the most that you would ever need to set the volume to is either 1 or 2.  Anything beyond that is obnoxiously loud for home use. 

Jason

[qbert]

Thanks Neonkiss, I thought the impedance change caused by the resistors may have had something to do with it. Some of the old A&P tech school memory is coming back.  Since I have a few LM1875Ts I'm going to try that just to get the board working again. The old coin ops I have also use this audio amp and they are touchy at best when not run exactly as designed. I'll post back to this thread when I get around to changing out the IC with the success or failure. I have a Rev B board if that does not work and will remove the resistors when I change to it. Maybe this is a warning to others but what other choice do you have if you have an older board and want back lit reels? Thanks for the K+ (whatever that is)

Also thanks for the input from Yoeddy. The game I have with no issues has a rev C 504 and the volume is also set on 1 and it is as loud as the one with the resistors (when it worked) set on 7. (may be overdriving the audio amp on the 504)

[Yoeddy1]

Rev C?  Such a creature exists?

Jason

[staz]

i set my 504B at 3 and its pretty loud......im becoming def in my old age   My other machine i set it at 5 but thats a enhanced board wnole different ballgame........... it def has to be the resisters..... i started out with a 504A and i tried resisters on it and the sound sucked......i had to have it at 10 to barely hear it.....your better off investing 50 bucks and getting a 504B board......

[qbert]

Sorry rev B (I can't type either)

[Yoeddy1]

Sorry rev B (I can't type either)

No worries man.  Cheers! 

Jason

[CVslots]

Rev C?  Such a creature exists?

Jason

A little off topic, but we came across a 504, Rev. IN....Has anyone seen this revision before?

 

[stayouttadabunker]

A little off topic, but we came across a 504, Rev. IN....Has anyone seen this revision before?

"IN" can mean a couple of things...
a couple of wild guesses would be "Indiana" or "Indian" ?  
I have no idea really...lol

[Yoeddy1]

I was thinking In A Gadda Da Vida.

Jason

[CVslots]

Could very well be Indian...Not sure if that is PC or if they would have used the term Tribal instead...so if that's it, I wonder what the revisions would be?

I was thinking In A Gadda Da Vida.

Jason

Good guess Jason...

[qbert]

Time to get back on topic.
I replaced the  LM1875T amp on the MPU board and the sound has returned. I still have the resistors installed since the static is intolerable with back lit reels on a rev A. I have turned the volume down to 3. I am now convinced that the impedance difference caused by the resistors is too hard on the  LM1875T. I know the Rev B board is the easy fix but they are pricey and the amp was less than two bucks and some time with the desoldering bulb. I was even able to retain my wife's hard earned credits with this repair. She is happy (at least for a little while). We need to come up with a better solution than resistors since this appears to be taxing on the boards amp.
Does anybody have any ideas?   
Also there was very little heat sink compound on the old chip.

Thanks for your views and ideas, I love this site!

[cowboygames]

I'm sure there's a better fix, but IGT fixed it by reworking the board for the 504b version instead of doing field repairs. I use 10 ohm resistors instead of 47 ohm on each of the six speaker wires and after 3 years for the oldest installed mod I haven't had any problems

[staz]

504b is the way to go you can find them out there for as low as 40 bucks.....thats really not that pricey considering the sound difference.....

[Buzz]

I'm sure there's a better fix, but IGT fixed it by reworking the board for the 504b version instead of doing field repairs. I use 10 ohm resistors instead of 47 ohm on each of the six speaker wires and after 3 years for the oldest installed mod I haven't had any problems

Rob  I'm with you, I wouldn't begin to try and guess how many machines this Mod has been to, I think I've done at least 25 or 30 and not one failure in the whole bunch.  Now all of a sudden one guy has two go bad and that makes the whole idea a bad idea.

I'm like you I didn't like what the 47 ohm resistors did to the max volume so I remove them and went with 22 ohm. Matter of fact I had a Williams Big Bang Pig Dotmation that was so load I put a resistor on it's speaker wire. As for as I know it's still working, I sold it a couple years ago and the new owner hasn't bitched.

[cowboygames]

Buzz, also says he went to the input side of the amp instead of the outputs to the speakers. That may be the whole difference putting the stress squarely on the MPU

[qbert]

Cowboygames you are correct. My machine indeed has the resistors on the input side. This is the way the game was wired when I purchased it.
It did function well for about 3 months of continuous use until the first failure. That is why I'm asking is there anything else. I do not want to go to rev B and suffer the same result because there is another issue with the game.   

[cowboygames]

Personally, I'd try the swap. Take those resistors off the inputs and use a smaller resistor on the speaker outs. One one each of the leads, both positive and negative sides

[qbert]

Update.
I did not get a chance to move the resistor packs to the speaker side. Played the game for a few days and MPU board sound failed again.
I have since switched to using the Rev B without resistors (and noise) and have had no issues.

Buzz I'm not saying the mod is a bad idea (especially if it works) but don't you think if the fix was this easy IGT would have had a nice plug in adaptor complete with P/N and price tag rather than redesign a circuit card?
I see another guy is asking about the resistors heating up, this is stress on the whole system.  I'm just trying to say putting in a resistor is causing an impedance problem in an audio circuit. What is really required is a filter of some sort (IE capacitor) basically we are trying to remove hum and noise caused by an outside source. IGT did it by changing the art work on the board. In normal audio circuits removing noise (like 60hz hum) is done with a filter capacitor not a resistor.

Thanks guys for your views it's stuff like this that makes the product better for all. 

[cowboygames]

The noise isn't AC hum. It comes from the reel motors and is gone or very negligible on boards that don't use a multimedia board and simm card. More like a grounding problem with the reel wiring I'd guess or a tie in between the reel ground and the multimedia board ground.

[qbert]

I was using AC hum as an example, whatever the source it is noise and noise can be filtered.
Thanks for your interest.