(Mad Dog: Did you ever find the PLL resistors on the 2300 motherboard?)
I'm not certain, but I suspect they aren't in a "bank" like we see on most other Macs. It will take some investigating to confirm, but I'll bet they are on the underside to the left of the PBX (big TI chip under the 603e, I think that's the PBX). There are a few empty resistor pads. It might be that because space is so precious on the Duo mobo that the resistors are spread out. Look at R79 through R109 - there's a semi-vertical column of resistors there... A continuity tester will tell if they connect to the PLL pins on the 603e. PLL resistors set the bus clock to CPU clock ratio. The 2300c operates at 3x the bus speed. Increasing that to 3.5x ought to be possible with the 603e, but the problem is finding the resistors!
I'm finally getting around to my stereo headphones hack.
It looks like pins 71 and 72 on the PDS are SND R & L (sound out right & left), respectively. Pin 150 is /SPKR SEL. Bringing that to ground will tell the PowerBook to turn off the built-in speaker, I think.
So. I've got a 4-pin stereo mini-jack I lifted off my 190 motherboard. The two smaller pins closer to the opening of the jack are clearly the left & right audio pins, but I don't know which is which. Does anyone know which segment of the 1/8" stereo mini-plug is right and which is left?
The two pins towards the end of the jack probably connect to ground (the tip) on the plug. I imagine that when you plug in a mini-plug, those two pins are connected. One of them should probably connect to pin 150 on the PDS. The other should probably go to ground either on the PDS or elsewhere. Can anyone confirm that this is the behavior of the jack Apple uses? Or that if /SPKR SEL is brought to ground that it will disable the internal speaker?
I'm also going to post this to LEM PowerBooks and the 68kmla, so I'm sorry in advance for the cross post.