800XE Low Sound Issue (except for the keyboard click 🤔)

[mmoec]

Good evening all.

I've searched the forums and I could not find anything specific to the issue I'm experiencing, but please excuse me if this has already been covered.

I recently purchased an Atari 800XE in excellent condition, but quickly realized that the audio was extremely low, except for the keyboard click which was normal (I found out that this sound is generated from the GTIA chip). I did some research and found some of the other components associated with sound and swapped the POKEY and LM358 and the GTIA as well, but this didn't help. I tried using the RF modulator instead of the monitor port to check for sound but the interference was so bad I couldn't tell, plus there was no color and bad vertical scrolling, so I simply eliminated it. The closest thing to a field service manual I could find was the 130XE manual which did covered the 65/800XE (C070067 Rev - B which is actually the same board as the 130XE just fewer RAM chips), under the symptom checklist it mentions components U24, L11, and L12, so I swapped out both multiplexer chips and both inductors, but still no go 🤷‍♂️. I'm at a loss as to where else on the board to check for sound issues, so I'm asking for some help here. I would greatly appreciate it if someone would take the time to point me in the direction I should go next. I can provide screen shots of the board if needed. Thanks guys! 🙂

[_The Doctor__]

are you sure it isn't a bad cable? also, if your rf is that bad, is the same display device being used for all your tests? might be the display and not even the Atari

no color vertical scrolling? bad cable wrong channel wrong system, fine tuning?

[mmoec]

PROBLEM SOLVED!!

 

I found 2 suspect looking NP caps in the same area as the L358 chip (C19 and C20, they both had small holes on top as if they had imploded 🤔). They were both 4.7uf 35v, the closest I had was 4.7uf 100v (I read up on it and apparently it’s ok to go higher on voltage, I hope 🤞), swapped out the caps and booted the machine, and I now have sound! 
Thank you for the replies, I’m glad this one is behind me, but I did pick up some useful info along the way 🤓.

 

[mmoec]

2 hours ago, _The Doctor__ said:

are you sure it isn't a bad cable? also, if your rf is that bad, is the same display device being used for all your tests? might be the display and not even the Atari

no color vertical scrolling? bad cable wrong channel wrong system, fine tuning?

I tried 2 different RF cables, I’m fairly certain the RF box was bad, but the issue has been resolved, it was the C19 and C20 caps that were causing the low sound issue.

Thank you for the reply 🙂

[_The Doctor__]

External RF switch box, understood.

 

Glad you found the issue. low audio caused by caps finally died out on the machine

Edited September 26, 2023 by _The Doctor__

[TGB1718]

7 hours ago, mmoec said:

(I read up on it and apparently it’s ok to go higher on voltage, I hope 🤞)

As long as they fit on the board, always safe to use higher voltage Cap's if that's all you have.

[mmoec]

1 hour ago, TGB1718 said:

As long as they fit on the board, always safe to use higher voltage Cap's if that's all you have.

👍

[TZJB]

On 9/26/2023 at 4:46 AM, mmoec said:

PROBLEM SOLVED!!

 

I found 2 suspect looking NP caps in the same area as the L358 chip (C19 and C20, they both had small holes on top as if they had imploded 🤔). They were both 4.7uf 35v, the closest I had was 4.7uf 100v (I read up on it and apparently it’s ok to go higher on voltage, I hope 🤞), swapped out the caps and booted the machine, and I now have sound! 
Thank you for the replies, I’m glad this one is behind me, but I did pick up some useful info along the way 🤓.

 

 

Thanks for sharing this issue.

 

Just my observations:-

 

I have never seen holes in the top of faulty capacitors like that. In fact they look like deliberate puncture marks, maybe caused by a probe?

 

C22 is also 4.7uF NP and might be worth changing.

 

Also what memory are you using? The main 64KB memory bank U9-U16 seems to be missing.