5 Sep
2009
5 Sep
'09
9:43 a.m.
If a simple fault really makes all or even most of the
signatures wrong,
then the test engineers didn't design the test mode(s) of the product
My experience is that the systems that are hard to debug are those with
multiple 'feedback loops' -- things like complex state-machine based
control systems. And with those any fault is likely to affect just about
every waveform in the system.
Signature analysis might be useful for simpler systems, but those are not
hard to sort out anyway.
properly. I haven't observed that problem with HP
or Atari products
that have documented signatures.
Perhaps that why few of the HP service manuals I have contain signatures
(I think the only one that does is the one for the 82163 HPIL video
interface). Any whay in at least one case (the HP7245A printer/plotter)
HP provided some extra circuitry on the processor board (a 7474
dual-D-type and bits) to control a signature analyser but didn't put any
signatures in the service manual. I guess the signatures would tell you
if it wasn;'t working correctly but wouldn't help you find the fault.
-tony