If reset is at 0.24V relative to ground, then the CPU is being held in reset.
It's an active low input, so it's active.
Measure pins 5, 6, and 8 of IC5 please.
Pin 5 should be roughly 1.1 volts DC.
Pin 8 should be 5.0 VDC +/- 0.1 volts
Pin 6 must be less than what you have at pin 5.
Also, make sure you have installed R35, as IC5 can only pull
reset low. The resistor is needed to pull it high when the IC is not
pulling it low. (Google "open collector")
If reset is asserted to the CPU, there is no point to look at any
other CPU pin except the two oscillator pins (with a scope, not the meter)
and the power pins. So 2,3,40, and 20. Check all 4 of these with the scope
and tell us what you see.
But it won't run until you get the reset issue sorted out.
Bob
--------------------------------------------
On Mon, 2/8/16, jw_dewdney@yahoo.com [PolySix] <PolySix@yahoogroups.com> wrote:
Subject: [PolySix] Re: The Post I wanted to make....
To: PolySix@yahoogroups.com
Date: Monday, February 8, 2016, 11:54 PM
HI Bob - sorry it took me awhile to dig the scope
out and find the probes etc.
So - I got it
all up and running and damned if i can see a signal
ANYWHERE. From both TP4 and from the RESET (pin 4 according
to the drawings i found) I get only positive DC offset and
no pulses whatsoever. I double checked my with my Tek TX1
dmm - which does a nice job as a frequency counter also -
and from TP4 I got 0.004 Hz (meaning zero) pulse activity at
plus 4.9v offset... and from the reset pin I get about
0.24mV dc offset (positive). I'm getting positive
offsets of betwen 1.5 and 5 volts on nearly every pin on the
CPU. TP1 gives me 0.6-ish volts positive - so maybe
that's got SOMETHING to do with it? Not sure. Still
driving me crazy why that should be... I'm trying to
follow the circuit back to the power connector but get a bit
lost when i do...
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