11/45, sick or not?

Tony Duell ard at p850ug1.demon.co.uk
Wed Jul 6 17:55:08 CDT 2005

> Joe wrote...
> >  Are you sure that the lights aren't blinking too fast to see? Perhaps you
> > can hang a logic probe (with a pulse extender) on one of the lights to be
> > sure.
> I'll try that tomorrow... but I wouldn't think that is what is happening. 

Have you tried single-stepping the program from the frontpanel? 

Be warned, though, that I had a particularly nasty fault on my 11/45. It 
would mess up branch instructions (and some others IIRC) but when I 
single-stepped it at the microcode level (I have a KM11 card), it all 
seemed fine. It turned out to be a chip that was 'going slow'....

> Also, pardon my lack of knowledge, but... shouldn't I be seeing the .2v 
> ripple as an AC component (ie. a sine wave)? It's a very clear perfect 
> sawtooth. And it's exactly the same on all the 5V regulators, which strikes 
> me as odd.

No, that sounds right. Even on a linear supply, the ripple is not 
sinusoidal -- it's an almost-linear ramp down as the smoothing capacitor 
discharges follwed by a little bit of a sinusoid as the capacitor is 
recharged. On a switching regulator (which this is), the ripple is likely 
to look even more like a sawtooth.

You might like to replace the output capacitors in your regulator bricks, 
but I really don't think this is the problem.


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