Burgertime audio issue

modessitt

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I'm working on a Burgertime cocktail at work, and I got everything working so far, but the sound is screwy.

When it first came in, I got no sound. Fiddling with the volume pot gave me some loud static, so I figure that means the amp is working fine. So I recapped the sound board, matching what was in there by value. Now I have sound, but i also have a hissing, squealing noise that gets worse as you turn it up. You can't turn it down enough to just hear sounds without the squealing.

I thought perhaps I might have replaced some caps that should have been tantulum with electrolytics, but the original caps didn't say they were tants (three 47uF 16v's looked silver metal).

So, I went to arcarc.xmission.com to check the manual, but the manual has the D333 version soundboard, and this is the B333 version sound board. All of the parts have different designators (for example - the three 47uf's are C54-56 on the B333 and C22-24 on the D333). There are some other layout differences, and one might have more or less parts than the other.

Of a more unhelpful note, it just lists the caps as 47uf. It doesn't list a voltage, or whether it's electrolytic, tantulum, or whatever. It does this with all of the caps in question.

The owner said that his volume kept getting lower and lower over time until it finally couldn't be heard.

Anyone have any insight for me? I'm thinking about putting the old caps back in one at a time to see if I can make the problem go away. That would at least tell me if one of them is the issue....
 
I've had a couple BurgerTimes just recently with hiss/static sound.....It was one of the NE555's that sit in front of the amp....IIRC, there's two in the audio circuit.

Edward
 
Wonderful. I'll bet I don't have any at the shop. Were they used on any other Midway stuff? Pac-Man perhaps? I have lots of those boards lying around....
 
Except you have to look at the packages carefully as they tend to just have the CMOS versions of the 555 timer. Those are lower power and will give different results. On Galaxian the sounds are a little faster if you use them.
 
My boss wants it finished by tomorrow. What's my best option for getting my hands on this part if I need one or two? I have a large stack of boards if I need to rob something until I get an order in...
 
Galaxian





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Hmm. I have one somewhere.

You were supposed to say something like Galaga that I have in an easier-to-get-to spot....
 
Well... you could always stop by Altex on the way to work.

Not sure if Austin still sells semiconductors. I know the Dallas location doesn't since I bought their stock. ;)
 
Well, when Bantam was around, I could get them there. The Altex here is only a few blocks away from me.

I wonder if Fry's would carry them?
 
Well, it seems a lot of the late 70's pinball boards have this same chip, and we have those all over, so I'm going to go thru them to see if they are EXACTLY the same, and try swapping some out (with sockets) to see if I can narrow it down...
 
You have any CPU boards for Gameplan? I need one for a Foxy Lady.
 
The little cocktail? I think we have one around here for a Sharpshooter, but it may belong to a pin we're doing for someone. And we have a little cocktail that's been here forever, but it's got battery damage all over.


As for the BT - I replaced the 555 with identicals, and still have the squeal/static. Just for fun I put the old caps back in and get the same thing - so it's not caps or 555's. I'm leaving it until Monday, but what's the next step - amp? Volume pot? The squeal/static sounds like what the old dial-up modems used to sound like towards the end of their connect protocol...
 
Next step is what you should've done first...

Use an audio probe or oscilloscope to track it backwards through the circuit.
 
Next step is what you should've done first...

Use an audio probe or oscilloscope to track it backwards through the circuit.

You obviously haven't been to my work. Our test equipment consists of licking our finger and sticking it on a chip to see if it helps. It's surprising I can fix anything...
 
Then you need a high impedance op-amp and a small amplifier circuit to build an audio probe with. That'll help you find the noise.
 
It's barely Monday! :rolleyes:

Looking into building an audio probe. Seems the easiest way is with a powered computer speaker, but I don't have one here...
 
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