So far, the only signals we have seen that looked reasonable
were ALE and the oscillator input. You have lots of signals
that show very small wiggles that look like capacitive coupling
from either the oscillator or ALE. So far, I haven't seen pics of
anything else that's changing. If the CPU were stuck in reset,
that would explain it. You did say something about the data bus pins
changing, except for 2 of them. But didn't post any photos of that.
Were they swinging 0-4V? Of course with the data bus, you need to
see who is driving it. If the RAM is enabled, that data may be coming
from it, and not from the MCU.
Anyway, hope you can try that 8048 in another Polysix. That would
certainly be a useful test.
Not sure what other chips could have failed that would cause the MCU
outputs to be so quiet. In the test mode code, it should be writing values
to the DAC over and over in a loop. The only thing it checks is the T0 input,
and that won't cause it to stall, just changes the digital value.
--------------------------------------------
On Wed, 7/6/16, noddyspuncture@hotmail.com [PolySix] <PolySix@yahoogroups.com> wrote:
Subject: Re: [PolySix] Another P6 with all LED's lit....
To: PolySix@yahoogroups.com
Date: Wednesday, July 6, 2016, 8:00 AM
Yes Bob, all those power pins to the 8048 are
fine...!
Although I am
actually getting waveforms and "activity" around
the 8048, it all seems to be in the millivolts and not at
logic levels as you say.
The Xtal osc is fine... but there
isn't anything on the 'clock' TP pin 32. And
Reset is sitting high.
I have checked each and every 8048
pin to see of it connects to all destinations on the
schematic and it's all fine so I think it must be component
failure somewhere, the problem is finding
it.
I am assuming that other
IC's having failed elsewhere could also give the
symptoms I have...?
I suppose if I buy one of those new
boards and transfer all my IC's onto it I'll still
have the same problem which would be annoying to say the
least...!?
I have a
friend with a Polysix - I'll see if he'll let me
swap the 8048's.
Cheers,Tom