Hello, my Apple IIgs is running perfectly except for the fact that there is no sound from the speaker or headphone jack. When I plug in my headphones I hear the initial static "pop" but nothing else.
The only multimeter testing Ive done so far has revealed that the speaker seems to have a short. There is continuity between the two leads at the speaker but not at the pin header. This would be fine if I could plug in external speakers.
Any ideas as to where to test from there or links to good service manuals?
Well, most multimeters will beep on continuity, since the resistance between the two leads of a speaker is very small - around 8 ohms. To check it, you can put your multimeter on ohmmeter and measure the speaker's resistance. It should read between 7 and 8 ohms if it's good.
Yes, absolutely correct.
Speakers should never go short (unless molten solder got spilled into the spider or the dust cap). They fail by going open circuit, when the fine wires that connect to the driver coil fatigue from constantly vibrating and break.
I've seen a few speakers fail short, but it definitely isn't the normal pattern (the one you describe). The only times I've seen it I suspect an overload signal went through and either melted the coil together or the coating on the coil wrappings and they shorted together. That seems unlikely in a IIgs because the amplifier doesn't have enough power to melt anything. Maybe some kind of power spike could, but you'd think something like that would fry something other than the speaker. Possibly heat could cause the coating on the coil wire to fail or exposure to some kind of chemical or corrosion? It's definitely weird.
Anyway, I only know for sure that there is something that can melt speaker coils because I've re-coned quite a few music instrument speakers over the years and I've run into a couple that needed the voice coil replaced or rewound. That is a pain in the butt to do and only worth it for vintage speakers. But yeah, usually they fail open, no continuity, probably 99% of the time.
Thank you for the replies. I'm more concerned about the headphone jack not working than the internal speaker. I'm just not sure where to begin troubleshooting that. Is it feasible to to diagnos issues with the Sound RAM, GPU, DOC and amplifier without an oscilloscope?
Screenshot_2025-05-06-12-53-06-56_3aea4af51f236e4932235fdada7d1643.jpg
I guess if you have amplified headphones, you can trace it even without an oscilloscope. The audio schematics are on the very last page: https://www.applefritter.com/files/2025/05/06/Apple%20IIgs%20ROM1%20Schematics.pdf
There's a capacitor, a resistor and an inductor between the output of the audio op amp and the speaker/headphone jack, which are (for all intents) more or less in parallel.
I'd start with the componentry in betwen the op amp and the jack and make sure that there is continuity, and that the capacitor is not blown.
Chances are there's an issue with the inductor...I've seen inductors go before on this machine.
The failure of one of the small electrolytic capacitors is much more likely, compared to a solid state component like a ferrite bead.
The 22 µF caps at SC2, SC5, SC6, SC13, SC18, SC20, and SC41 should all be checked. There may even be tell-tale wetness beside one or more of them.
Good point. I should have looked on the motherboard before I spouted off about failed inductors, becasue these particular ones are basically wires threaded through a bead.
Mind you, I haven't come across failed capacitors on a ROM 1 yet, but that does seem the most probable culprit.