Help with Atari 2600 PAL that loses sound after some time into game play

[soon]

Hi, I have an Atari 2600 6 switcher PAL that produces distorted audio about 1 minute after power up, and slowly loses audio after few minutes into game play. The problem persist even powering off and on again. The audio will be ok again after leaving it unplugged overnight. I have attached a video of how it sound. Note that this Atari 2600 is AV modded, so the red coil has already been removed. Both the RIOT chip and TIA chip has been replaced recently.

 

Here are a few things that I have tried but doesn't help:

1. Change another 9v power adaptor

2. Make sure power toggle button has good connection

3. Checked output from the power regulator is always 5.1v

 

Hope to get some pointers as to what are most likely cause of the problem. Thanks in advance!

 

[Voxel]

I'm thinking there may be a bad capacitor, and would suggest replacements at this point.

[Cmherndon79]

Yeah, there are 2 820 pF polystyrene at C206 and C207 that handle the audio and these tend to fail in the way you're describing.  When I work on these I always proactively replace them with new MLCC caps.

 

Info:  https://console5.com/wiki/Atari_2600#Styrene_Capacitors

[soon]

23 hours ago, Cmherndon79 said:

Yeah, there are 2 820 pF polystyrene at C206 and C207 that handle the audio and these tend to fail in the way you're describing.  When I work on these I always proactively replace them with new MLCC caps.

 

Info:  https://console5.com/wiki/Atari_2600#Styrene_Capacitors

Thanks for the suggestion, but this is a AV modded unit, the audio goes directly from the TIA PAL pin 13. 

[Cmherndon79]

Huh.  Interesting.  I've done a lot of AV mods, but never pulled audio from the TIA chip directly.  For the 6 switchers I always remove Q202 and pull audio from the empty hole connected to C210, appears to be the same on the PAL version as the NTSC board.

[soon]

8 hours ago, Cmherndon79 said:

Huh.  Interesting.  I've done a lot of AV mods, but never pulled audio from the TIA chip directly.  For the 6 switchers I always remove Q202 and pull audio from the empty hole connected to C210, appears to be the same on the PAL version as the NTSC board.

Hi Cmherndon79, sorry for the confusion, I don't mean directly from the pin. What I have tried is to follow the 2 guides below to install the AV mods:

1. http://www.coolretroprojects.com/Atari_2600_AV_Mod_Installation_Guide.pdf

the instruction asked to tap audio from TIA pin 13, before C210.

 

2. https://www.thefuturewas8bit.com/atari_2600_6_pal

the instruction asked to remove R209, and have the audio tap from one side of the removed resistor, after C210

 

I have tried the above 2 with the same result. In both cases, I believe the audio signal will not pass through C206 and C207 as I have already removed R209. I have attached the PAL schematic diagram that indicate where I tap the audio signal.

[Cmherndon79]

Hi @soon

 

Always interesting to see different ways of doing things.  I've bought some C64 stuff from The Future Was 8 Bit.  Back when I started doing Atari refurbs and mods, I used this as a guide:  https://vintagegamingandmore.com/installation-guide-6-switch/ . But yeah, looking at the schematics it is coming right off the TIA.  The component locations are different on the NTSC version, but the location numbers are the same, so I ran a test on a Light Sixer I had here that I've been meaning to look at due to a hum in the audio (it was a TIA problem, swapped and it sounds normal now).

 

I removed R209 and C206 and C207, put in Frogger about 20 minutes ago and the sound is working fine still.

 

Being there isn't much there, you're getting audio for the first minute of use, thinking you might have a TIA issue.

[soon]

On 11/22/2020 at 8:33 AM, Cmherndon79 said:

Being there isn't much there, you're getting audio for the first minute of use, thinking you might have a TIA issue.

Hi @Cmherndon79, I replaced another TIA and the problem is solved ? Thanks a lot for your suggestion.

[Cmherndon79]

Awesome @soon!  I've got a half dozen TIAs that I've pulled from systems due to various audio issues.  Haven't run across one that starts out working and then stops yet.  Most have one channel missing and I know I've got one that introduces an audible him and another that has the 2 channels with their timing off, which makes for some entertaining audio.