Gauntlet audio distortion

mjenison

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Hi all,

My Gauntlet PCB has perfect audio on the right channel, but the left channel sounds like it's coming from an old record player (slight crackle, audio is tinny). All audio tests pass. Wiring and speakers have been eliminated as causes. Any thoughts on what component might be the issue? Any tips on how to debug audio issues like this?
 
The good side is that the audio is coming from the smaller audio pcb.
Check to see that the wires going to the 6-pin connector are connected to the audio pcb properly.
Also check to see if the speakers are connected properly on the back as well as to see that one speaker is not blown.
Being the speakers are made of paper, you might have one of the speakers blown.
 
"Easiest" way to troubleshoot many problems is often to swap in known-good major component. Of course, that's not always a viable option...

If you've eliminated the wiring and speakers as potential sources of the problem (and I'd be interested to know how that conclusion was reached) the next suspect is likely the ARIII. Swap in a good one if you can. If you can't, check for bad caps on left channel circuitry. The amplifier IC (TDA2030) could also be the problem.

If it isn't the ARIII, go to the PCB; there a coupling cap for each channel there, and just upstream from them are LM324 op-amps.
 
Probably should have stated that the board is Jammatized and testing it out of my Jamma cabinet.

The tinny-ness can be discounted; tested with another stereo board and that speaker is just more tinny than the other. However, the crackle follows the board. If I play a sound out the left side, I don't hear any crossover noise out of the right channel, but if I play a sound out the right side, I can hear a "sizzle" from the left speaker that mirrors duration of the audio coming out the right channel. Again, this just applies to this board; other stereo boards have no audio symptoms like this out of the same cabinet.

Tried replacing C57 (10uf / 25v) but no change.
 
Dumb question: How does one "JAMMAtized" a Gauntlet PCB? AFAIK, Gauntlet's audio output is low-level; and JAMMA expects an amplified audio output (straight to the speakers). There has to be an audio amplifier somewhere, right??

Tried replacing C57 (10uf / 25v) but no change.

Yeah, that's the output coupling capacitor I was referring to.
 
Dumb question: How does one "JAMMAtized" a Gauntlet PCB? AFAIK, Gauntlet's audio output is low-level; and JAMMA expects an amplified audio output (straight to the speakers). There has to be an audio amplifier somewhere, right??

The output of Gauntlet audio is loud enough to not require amplification (can be heard clearly without it).
 
[...]this just applies to this board; other stereo boards have no audio symptoms like this out of the same cabinet.

Do you mean that switching the gauntlet PCB with another, different, PCB the sound is ok from both the speakers?

In origin that board (like all the atari boards of those ages) had an external, not built in, audio amplifier, so probably the jammatization of the board is not "complete" (in other words you need the ampli to run it 100% even if the output is "loud enought")
 
Do you mean that switching the gauntlet PCB with another, different, PCB the sound is ok from both the speakers?
Yes.
In origin that board (like all the atari boards of those ages) had an external, not built in, audio amplifier, so probably the jammatization of the board is not "complete" (in other words you need the ampli to run it 100% even if the output is "loud enought")
I would think adding the amplifier at this point would only amplify the distortion, not resolve it. Also, how would that account for the right channel sounding perfect?
 
In origin that board (like all the atari boards of those ages) had an external, not built in, audio amplifier, so probably the jammatization of the board is not "complete" (in other words you need the ampli to run it 100% even if the output is "loud enought")

+1 on that. I don't think the audio output op-amps on the Gauntlet board are designed nor intended to drive 4- or 8-ohm speaker loads. Even if it's loud enough, that doesn't make it right. If it were mine, I wouldn't use it without hooking up an external audio amp.

As far as your problem... The schems are here: http://arcarc.xmission.com/PDF_Arcade_Atari_Kee/Gauntlet/Gauntlet_SP-284_1st_Printing.pdf

Audio mixing & pre-amplification are on the right part of sheet 6. I might start with the LM324 @ 15/16U...
 
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