On Friday, December 29, 2017 at 11:23:08 PM UTC-5, Paul Hovnanian P.E. wrote:
Tim R wrote:

[snip]

What am I missing? I've tried speakers, amps, cables, and software, I
don't know where to go next. Oh, maybe should mention, this is an older
laptop. It came with System 7 but when the harddrive crashed we couldn't
get another 7 without paying the cost of another laptop so we put on XP.

Old laptop may have a slightly recessed audio jack. So a standard mini plug
won't seat fully and make connection with left and right channel contacts in
the jack.

--
Paul Hovnanian
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I bet the human brain is a kludge. -- Marvin Minsky

That makes sense. I have 3 cables that don't work, but an iPhone earbud does. The cable in use upstairs also worked, so maybe there's just enough variation from plug to plug.

So you think over time the jack has depressed a bit, just enough to not make good contact? The answer then is probably to get sound out of the USB instead of the headphone jack.