Re: Apple II Minus Question

[mjmahon@aol.com (Michael J. Mahon)]

Bryan Parkoff wrote:

>    I give you an example.  GR and HGR are not working on second motherboard
>while Old Monitor Routine is not powered up on first motherboard.  I tried
>to swap ALL 74xxxx and DRAM chips from working motherboard to both defective
>motherboards.  The status is still the same.  There is no solution for Old
>Monitor Routine Start-Up and GR & HGR working.

If you have properly switched the chips with a working main board
and the fault did not "follow the chips", then you have demonstrated
that the chips are OK and are not the problem.

The problem is in what was _not_ different in the non-functioning
system--the main board.

>    I must admit that it is necessary for me to purchase electronic
>diagnostic equipment to test three defective motherboards.  I still have
>voltimeter.  Is it worth to obtain several different diagnostic tools?

Hardware "diagnostic tools" are needed to diagnose hardware
problems that make the system incapable of running software
diagnostics.

I assume that you already have a Volt-Ohm-Milliammeter,
preferably with an audible continuity test capability.

If you know your way around digital circuits, I'd suggest at least
a logic probe and a logic pulser.  An oscilloscope is essential for
more advanced work.

Since many board problems are mechanical in origin, I'd also
suggest a good light and a magnifying lens.  For temperature-
related problems (not so common on an Apple main board) some
canned "freeze spray" is a good investment.

And, of course, a good, temperature-controlled soldering iron
with a clean damp sponge, some good fluxed solder wick, and
some small-guage rosin core 60/40 (or 63/37) solder is essential
to make repairs once you've found the problem.

-michael

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