Software Counter/Oscillascope

[Byron G. Jacquot]

>I've been over the circuit board dozens of times checking 4 broken 
>traces and the such, tested 100's of parts, but with no avail.
>The last thing that i feel sus about in this unit is maybe the CPU 
>clock and/or "INT Clock" (is this interupt clock?) is mis aligned.
>The "Int clock" adjustment is made via trimmer TM1 while the CPU is 
>one of those tuning coil "thingie majigs".
>I asked this question on AH with no responce about what the symtoms 
>of an mis alligned CPU clock and INT clock would be in an XOX 
>machine???

I seem to recall that the int clock is being used to do the panel scanning.
Every 1.8 mS, it tells the processor to try to look at the next group of
buttons.

If the clock were misaligned, there might be two different scenarios.  If
the period were too long, it wouldn't be watching the buttons as often, so
it might seem a little sluggish or unsreponsive when you push buttons...but
I'd venture a guess that it's have to be significantly slower than 1.8 mS.

If the clock were faster, yopu might find that buttons didn't register,
because the scanner would move on before the contacts on one button were
done bouncing.  I think that if the Int clock is sick, the switch scanning
will be sick.

>I've been working 4 a couple of weeks now on a non funtioning 606, 
>all the sound generators are fine, yet it refuses to write anything 
>to memory (playing previously stored patterns and tracks work 
>though).
>this might not be the case as it has no problems playing back 
>previously stored patterns and tracks, just anything involving 
>writing to memory.

Check the health of the "-WE" lines to the Ram chips.  When you're writing a
pattern, those lines should be hopping up and down a bit...of course without
a scope, they'll be very hard to see...those cycles are probably darned
quick...guessing somewhere in the 1 or 2 uS range.

Even if you don't have a scope, at least check the continuity between them
and the glue logic that generates -WE...and then from the glue back to the
processor.  It could be that the Glue is dead...assuming all of the above
suspects are getting power.

Byron Jacquot