Gauntlet II Audio Fades Away

hepgeek

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Finally getting around to working on a Gauntlet II 2-player that I recently picked up from an ex-operator.

When I switch it on, the attract mode music plays (the organ bit) then it tapers off (getting quieter) till nothing. Sounds like the voltage to the speakers remains after the taper (speakers still buzz if I turn up the pot, speakers also pop when I switch it off).

Should I suspect something on the audio regulator board, or might it be something on the game board? Any of you Atari gurus encountered something similar, or suspect it could be the fault of something in particular?

Some additional info: Monitor is DOA (thinking bad fly back, there's a bunch of brown ooze coming out of it) and was unplugged from iso power when I got it, so I can't access the diagnostic tests or see what else the game is doing. Red LED on the game board lights up and stays strong while switched on. This game is immaculate (aside from dust) in every other respect, so I suspect it had some issues then got stuck in the back of a warehouse for 30 years. I'll post some progress photos soon, it's like a time capsule.
 
considering you still have amplifier hiss, you can rule out a lack of +12V.

I don't know if these have AR2s or AR3s, but it looks like they're really easy to switch over to a switching power supply and/or wire for JAMMA. I found this site that tells how in the Tech section: http://www.ionpool.net/arcade/gauntlet/main.html

I'm looking at a picture of the board on system16 and I can't see where there's an amp on it, but judging by the pinout for the power plug it uses +15 and -15 (which would go to +12 and -5 on a switcher) so it has to have some amp somewhere on the board.

my advice would be to go switcher first and try again from there. also whenever you're in doubt about problems, always start with power first, then socketed chips second. the chips can just be pressed down on and if it makes creeking cracking sounds, you're doing them good. but also you can feel around to see if any are getting abnormally hot. the sound CPU is a 6502 chip, I would start there. you can try turning the game off and back on when the sound drops out -- I would think if it works when you reset the game that it won't be a heat-related issue causing the sound to go out.

try that and report back.
 
i have a gauntlet that was doing the same thing and swapping out the 4 caps on the amp cured it. it didnt have an ARII but a separate audio board. i cant remember but i think the caps were 3300 uf not sure if yours would be the same.
mine looked like this.
 

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mine looked like this.

Yep, mine looks just like that. I'll add those caps to my upcoming parts order. Do you think it's worth-while it to replace the amp transistors while I've got it out?

In the meantime, I'll take mecha's advice and do some chip poking/reseating and some in-depth multimeter work to see if I can't track the bugs down that way.

Thanks for the help!
 
i changed the amp in mine first and it didnt make a diff. i tried the pot also and the same thing . for me it was the caps but they didnt look bulged and i didnt have a cap tester at the time . i ended up needing one of those for a monitor i was trying to bring back and only one of the four tested within 10% ( i have a cap tester now)
 
ah I should've known it had an amp like Sprint.

transistors either work or they don't. so you shouldn't need to replace them. caps however dry out. I didn't even consider caps. been a long weekend.
 
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