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coppertj

Sound Failure on Atari 65XE

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Hi guys its been a while since i posted on the forums :D however,

My sound (monitor output sound, don't have rf box) is not working.

I did a couple measurements with the multimeter on the POKEY and it seems that it does have voltage output at pin 37 (read that on forum where someone had the same audio problem with their 130xe)

Personally, I have a hunch that it's not the POKEY chip itself rather it's a capacitor or resistor in the sound circuit since I'm pretty sure POKEY handles I/O and keyboard scanning (both of which work tested the disk drive with emulation with aspeQt/SIO2PC, however cassette playback does not work.)

 

So I guess my question is should I just skip trying to get a donor POKEY and attempt to troubleshoot the sound circuit (potentially just shotgunning the entire circuit and replacing it all until it works)?

I would gladly accept any advice from anyone! Thank you!

 

I have the schematic of all the resistor/capacitor values here http://www.jsobola.atari8.info/derelit/xefsm.pdf

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i had a similar issue some time ago and it turned out to be a single resistor. check the values in situ at first and it might give a hint.

if you havent already, include "130xe" in your searches as the boards are the same

 

 

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So I have an update, I finally got around to doing this 4 months later and I figured out all the resistors in the sound circuit are good and it wasn't a rf modulator short circuit. I measured all the capacitors resistance and found C19 (4u7) going to infinity. That should honestly be why the sound is not working because everything else in that circuit is correct. I'll keep this updated when I get around to replacing the capacitor.

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I'd not seen this thread before.

If there's no sound you can play the elimination game fairly easily.

If you get keyclick then the sound circuit should be OK.

If you have a tape drive then connect it and POKE 54018,52.  POKE 54018,60 in seperate lines.  That should generate a click, and sound circuit probably OK.

Of course, no sound could also simply mean the TV's not tuned properly on RF.  Or wrong plug used if it's a monitor breakout cable.

 

If you have an oscilloscope you could probe the audio pin direct from Pokey.

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Posted (edited)
34 minutes ago, Rybags said:

I'd not seen this thread before.

If there's no sound you can play the elimination game fairly easily.

If you get keyclick then the sound circuit should be OK.

If you have a tape drive then connect it and POKE 54018,52.  POKE 54018,60 in seperate lines.  That should generate a click, and sound circuit probably OK.

Of course, no sound could also simply mean the TV's not tuned properly on RF.  Or wrong plug used if it's a monitor breakout cable.

 

If you have an oscilloscope you could probe the audio pin direct from Pokey.

 

GTIA bell (keyboard click) is not making it through the sound circuit, POKEY isn't getting the SIO cassette audio data/fails the POKE tests, and I already snipped off the pin 5 RF leg eliminating the RF modulator from the equation, I also probed the POKEY a couple months back but it was in spec. It's probably just that c19 capacitor which is on the SIO audio line. I have one shipping to me now.

 

https://archive.org/details/Atari130XE_Schematics/

Edited by coppertj

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8 hours ago, coppertj said:

It's probably just that c19 capacitor which is on the SIO audio line.

You should be able to test that cap pretty simply to see if it’s shorted to ground or failed open. If you can desolder it more or less intact, you ought to be able measure capacitance out of circuit with even a cheap digital multimeter. 

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