JDM PIC programmer question

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I just built a JDM programmer (http://www.jdm.homepage.dk/newpics.htm )
and am trying to bring it up.

I noticed that the CLK line (pin 6 on the PIC) is going between -.7V
and 0V depending on the state of the RTS line on the serial port.  The
-.7 looks like the diode (D3) from the ground line clamping the
negative voltage off the serial port.  The GND level source isn't as
obvious to me.

Regardless, I'd expect the signal to flip between 0V and 5.1V (the
zener diode, D2).  Does anyone have any idea why I'd see these two
voltages?  The Data line's voltages also look weird to me... but the
MCLR, Vdd and Vss look exactly as I'd expect them (13.26V, 5.1, 0V).


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