I had some time today so I did the diode mod and tested with an internal BlueSCSI v1.1 using a IDC 50 to DB25 adapter.
I used the same SD card from my previous post and didn't have any issues.
Boot up video here: Macintosh Plus Booting BlueSCSI
I booted a similar setup last night with my newly repaired Mac Plus and thought I would share what worked for me.
I have not done the diode mod on this system yet so I'm powering the BlueSCSI v1 off a power bank via USB
Attaching my BlueSCSI LOG.txt for reference
Can you bypass the switch in the headphone jack with a jumper wire?
Maybe the port is just shot or corroded inside.
I think you would need a scope to properly diagnose the sound chip. Above my level of knowledge.
The ohms you are seeing on the meter make be believe the speaker is good too.
Mine was open circuit so defiantly bad.
Test continuity from the speaker back to the board on both wires to rule out a broken wire to the speaker.
My classic II speaker was dead too. I replaced mine with one from a Macintosh SE. The ohm ratings printed on the back of both speakers were the same so I drilled out the rivets on the classic II speaker and replaced with the SE speaker
I don't know the history of this machine but it's really clean inside and out.
At boot the machine chimes but displays a Sad Mac error 01FA00.
Searching around and it seems like a Mac Plus should not throw an 01xxxx error.
I've tried swapping the ram chips around but got the same result.
The Classic II was completely dead when I got it.
I cleaned and recapped the logic and analog board and it booted right up but with no sound and the screen seemed a little dim.
I tested resistance on the speaker and found it was open loop and replacing with one from a SE/30 (same specs as...
I'm not sure the chips for 8MB or 16MB SIMMs are documented anywhere but I have seen posts where folks have made them using the same boards. The ebay seller I got my SIMMs from is https://www.ebay.com/str/memorymasters
They were super helpful. I messaged them with the link to the...
So the system freezes when I plug in or unplug the headphones while the machine is running. If I plug the headphones in while the system is powered off I don’t get a boot chime but audio from the headphones is nice and loud.
I just buzzed out all the sound chip pins in the image you provided and everything checks out.
Interesting thing is I do get low volume sound when booted into the OS from the sound control panel but no boot chime.
Any other thoughts?