More Bringing up a CPM

From: Dwight Elvey <elvey_at_hal.com>
Date: Wed Jun 2 13:22:50 1999

"Richard Erlacher" <edick_at_idcomm.com> wrote:
---snip---
> It worked quite well with the fastest DRAMs and it had features I
> never got around to using, yet it was not as interoperable as the rather
> "schlocky" SD Sales board.

Hi
 I have an SD Sales board but didn't try it. I'd modified
it so that I could run RAM all the way up to the video
board in my Poly88 and still do a full 48K. This was in
the older days when 16K DRAM chips were costly. I've
since populated it with 64K and don't need the additional
address decoding so maybe I should try it. I'll have
to remove the IC I dead-bugged in place of the address
switch.
 Since I got the Static RAM working, this is a less pressing
issue.
 On the subject of LA/scope/logic probe/voltmeter. I personally
consider a LA as the shot gun approach. It will often find
problems when one has no idea where to look. The only problem
is that someone with an oscilloscope can often have the
machine repaired by the time one gets the leads connected
and the LA setup right. Still I have used LA's in the past
when nothing else would worked.
 I rarely use a logic probe because I don't have one. I
can use an oscilloscope just as well with the additional
features that an oscilloscope can provide when needed.
It is like a logic probe with more added.
 Still the best overall trouble shooting tool I have is
an analog voltmeter. I can move quicker with one of these
than many can with other tools. As far as I'm concerned,
DVM's are only good for setting power supply voltages.
I have one ( an accurate 5 digit unit ) but the analog meter
is still the first thing I reach for.
 I find that most don't know how to trouble shoot. The
sequence is simple but many still don't get it:

1. Observe symptoms
2. Make predictions
3. validate predictions
4. If predictions do not pan out add this
    to the observed symptoms and go back to step 2 or 1.
5. Repair bad part.

 I find that most don't understand the importance of steps
2 and 3. They try to go from 1 to 5 and usually it doesn't
work. Step 2 does require that you understand what to
expect from each kind of failure.
Dwight
Received on Wed Jun 02 1999 - 13:22:50 BST