Editing Atari STE Troubleshooting Guide (section)

== DMA Sound Troubleshooting (STE-Specific) ==

The STE's DMA stereo sound system is handled by the GST Shifter and GST MCU together, with the LMC1992 mixer chip controlling output levels:

<templatestyles src="Template:StyledTable/styles.css" />
{| class="wikitable styled-table"
! Symptom !! Possible Cause !! Recommended Action
|-
| No DMA sound, PSG (YM2149) sound works || GST Shifter not outputting DMA audio; LMC1992 mixer fault; 8 MHz SCLK oscillator failure || Check the separate 8 MHz oscillator near the GST Shifter (not the main 32 MHz crystal). If SCLK is dead, DMA sound will not function. Replace oscillator. Check LMC1992.
|-
| DMA sound plays but is distorted or at wrong speed || GST Shifter DMA rate registers incorrect (software issue); SCLK frequency incorrect || Verify with multiple programs that use DMA sound. If all are wrong, check SCLK oscillator frequency with oscilloscope (should be 8.000 MHz).
|-
| DMA sound only on one channel || LMC1992 balance setting incorrect; failed channel in LMC1992; broken trace on one audio channel || Check software mixer settings. If stereo balance is centred but only one channel works, suspect LMC1992 or trace fault. Test with headphones on the audio output.
|-
| No sound at all (neither PSG nor DMA) || Audio output path fault; failed coupling capacitor in audio circuit; monitor cable fault || Check audio output on pin 1 of 13-pin DIN. If no signal present at all, check output caps (C216 area). If signal present, check cable and monitor/amplifier.
|}