ALE looks great.
OK, the signal on pin 1 is 6 MHz, so it's probably simply capacitive
coupling from the adjacent pin 2, which is the main oscillator signal.
In other words, this signal is not changing state.
With crystal oscillators, unfortunately, many times the schem doesn't
show which is input and which is output. One will be a smaller signal
closer to a sine wave (that's the input to the osc) the other will be a larger
signal, closer to a square wave. That's the output. I suspect you are on
the input. Better to look at the output. Also, scoping the output is usually
safe, but putting a scope on the input can stop the circuit from oscillating
or change its frequency. Anyway, I think the oscillator is probably OK.
Power cycling just means turning the power off and then back on once. Not
over and over or anything.
What are you using as the scope ground?
Also, when displaying waveforms, I think it's best to first show the waveform
in a scale that matches how the CPU sees it. In other words, pick a place on
the scope for ground and use that same place for all of your pictures, so that
we know where ground is. Then set the scope to 1 volt/div, since these are
5V logic levels. That way we know right away if the signal will be considered
a "1" or a "0". If the picture shows a low amplitude high freq noise, I can't tell if
that's at 0V DC (low) or if it's at 4V (high). THe hf noise is just the 6 MHz of the
main oscillator, which makes me wonder how you are grounding the scope probe.
Also, we wouldn't normally look at a digital signal at 20mV/div unless we are
interested in the noise level. At this time we are more interested in whether
signals are sitting low or high, so zooming in to show us the noise is not really
that helpful. All digital systems will have some noise on the signals, but it's
usually ignored.
Pin 6 is INT, not INH. Looks like it is not switching, but I can't tell from your
photo if it's 0 or 1.
Pin 4 of the DAC is a current output, so you can't really scope it. We are
interested in the voltage output of the DAC, which would be the output of the
op amp that is fed by pin 4. The number isn't on the schem that I can see,
but I think it's pin 1 of IC27. That would be the one to look at with the scope.
So anyway, sorry but I can't tell much from your photos as they are sort
of focused on the noise in the system, which is the thing that digital systems
are designed to ignore. We need to zoom out and look at these signals from
a 0-5V distance, not see how much noise is on them.
We need more waveforms like ALE, even if they are flat lines. That will tell us
what the logic levels are.
If you do take more photos, please include the DAC voltage output, and P20 and P23.
Those are signal names, not pin numbers.
The "normal" trigger mode in many situations would be DC, IMO. THen you should have
a control called trigger level, and also a +/- selector. WIth these controls, you select
either a positive-going or negative-going section of the waveform as the trigger point,
and also the exact voltage level at which to trigger. If you don't use the trigger level
control, then AC might be the only mode that would work, since you are not setting
the level to match the DC level of the waveform.
Some of your photos look like the result of not triggering the scope at a consistent
place in the waveform.
Bob
--------------------------------------------
On Mon, 7/4/16, noddyspuncture@hotmail.com [PolySix] <PolySix@yahoogroups.com> wrote:
Subject: Re: [PolySix] Another P6 with all LED's lit....
To: PolySix@yahoogroups.com
Date: Monday, July 4, 2016, 7:25 AM
Hi Bob,
I
uploaded a few photos of my oscilloscope shots into a folder
called "Tom's" in the photos section here. I
named them to include the time & volts settings but
unfortunately the names were cut off... so I've included
the time & volts division settings for each one
below.
I'm not
sure what you mean about "power cycling"... do you
mean repeatedly turning the synth off and on in between
turning the controls...?
Nothing happens to the DAC output
waveform when I turn those controls in TEST
mode.And Pin 6 on the 8048 is sitting
HIGH
Pin 32 has a
waveform - the one I called 'washed out' or
'blurred'. It isn't an actual pulse like the one
on pin 11, as you can see... it's not a single line but
a mush of weak looking lines all together. That is how I
tried explaining the difference.
When I switch the test switch it
stays much the same just becomes smaller in
amplitude.
The oscilloscope shots I've
uploaded are -
Pin11: ALE (2v/.5uS)
Pin1: T0 (10mV/.5uS)
Pin3: Xtal (50mV/.5uS)
Pin4: Reset (20mV/.5uS)
Pin6: Inh (50mV/.5uS)
Pin32: in normal mode (50mV/.5uS)
Pin32: in test mode (50mV/.5uS)
DAC pin4: output (1V/2uS)
Cheers,Tom