Apple IIgs question..

Hi, all.. ( Gee, I get to ask a legitimate classic comp question.. ) Anyways, I've a A2GS sitting here, that I've been beating myself over the head with for about two days now.. (Yes, I'm stubborn) I've been trying to get ADT (serial) working between the GS, and my PC. I've gotten it to work just fine PC -> GS. (I even had my PC type a copy of Dos3.3/ADT/ADTgs in via the serial port at 300baud.) Anyways the stumper is in the GS -> PC direction. Nothing works. I've tried the modem port on the GS, as well as 2 different super serial cards. I finally got desperate enough to pull out a RS-232 break out box, and a scope. (Plus a couple of dweebie basic programs) What I find is the Apple serial communications looks like its running at about +/- 4v. (This is on the builtin modem port. I can't get a SSC to work either.) (The waveform also appears to have a fair amount of ring on the voltage swings, but that may be normal) I'm guessing that the +/-4volts isn't enough for my PC to recognize it. Question #1: Does anyone have any thoughts about my theory that the PSU is weak, or suggestions where else to look? Question #2: Presuming question #1 is reasonable, schematics for a GS PSU? Thanks, David