Fixing Mac Plus sound/speaker

[DrJosh9000]

I have a Mac Plus I'm repairing and cleaning up bit by bit. The next major problem is the internal speaker not working.

Via the 3.5mm audio jack on the logic board, I can tell it produces audio correctly so the speaker must be busted. I don't know how it broke. Maybe overdriven? Plenty of white noise out.

Without removing the white protective cardboard I can tell it's a 63ohm 0.25W speaker which is riveted to the analog board, with wires going near the cables going to the logic board.

What I don't know (yet) is:

* Is the speaker connected directly to the audio out from the logic board, or if there's any other circuitry/amplifiers involved on the analog board that could be broken? classicmac2.pdf is no help here.

* Anywhere to buy a replacement? Fallback plan is an impedance matching transformer. Problems?

* How to cleanly take the rivets out and the old speaker off without doing too much damage? Or not bother and glue the replacement elsewhere?

* Other thoughts?

 

[Macdrone]

The speaker is connected directly to the logic board.  I would almost guess its unplugged.  I personally have never seen one go bad but anything is possible at this age.  If you do have to drill it out, new rivets will cover it right back up.  I have replaced ones on the classics that way.

 

[jack]

A good way to test the speaker on the A/B is to remove the A/B and connect some leads from your favorite audio producing device (Cell Phone, CD player, etc.) to the speaker directly.

I think the speaker sound goes through a few other pieces of circuitry on the logic board than the headphone port does. But this is very likely not the source of failure.

 

[jgk]

If you're getting solid, expected volume audio out the audio jack, then the circuit that's amplifying the audio is likely fine, and it's just your speaker. The schematic I have shows R1 (27Ohm) between the audio jack, and the pin going to the analog board that's connected to the speaker, so I'd check that too. Oh, and the audio jack itself has an embedded switch that disables the path to the speaker when something is plugged into the jack. Might want to check that too. 

 
 

 

[jgk]

Correction to my above post: I was (erroneously) looking at the original Mac schematics, not the Mac Plus.  Looks like it's R22 on the Plus.

 

[DrJosh9000]

Thanks for the info all! I'll probably be having another go at it this week, will report back here.