My SE/30 has developped distorted sound in 2026

[Mu0n]

This SE/30 has been logic board recapped around 2019, it was my 3rd or 4th ever soldering job and I did a passable job of it with tantalum caps.
Its analog board has yet to be done as well as the power supply. It's been a stable workhorse and I've even left it running for days uninterrupted for #MARCHintosh.

Here's a recording from Super Studio Session in 22 kHz, but running a Studio Session song of 6 channels:
Pay attention to how every instrument has this rough distorted feel.

Here's a recording from Studio Session (so, 11 kHz) running the same song, but from my Mac Plus:
Every instrument is immediately clearer.


Before you think this is a System 7.1 on the SE/30 vs a System 6.0.8 on the Plus issue, consider the following: on the SE/30, the sound becomes PRISTINE again if I use the headphone jack instead of relying on the internal speakers.

I know that if both the speaker and heaphone sound output are problematic, it points to a sound chip problem, but what does it mean when only the speaker quality is bad?

 

[techknight]

Missing one-half of the waveform. Either the upper or lower transistor failed in the audio output stage, or you are missing the -12V.

 

[Mu0n]

Missing one-half of the waveform. Either the upper or lower transistor failed in the audio output stage, or you are missing the -12V.

ok, those are good avenues to test. -12V seems like the low hanging fruit, I'll check my external floppy drive port, I think?

How do I test these transistors? The sound chip is UE10, correct? This is what I have that I think is the most relevant schematic page for the SE/30

 

[YMK]

Q1 and Q2 form an emitter-follower output stage.

Check for the the +12/-12 supplies at each collector.

If the upper half of the output is distorted, replace Q1.

If the lower half is distorted, replace Q2.

Be aware, they are different parts.