Repair methods (was Cromemco 3101/Beehive B150 score)

[Tony Duell]

> Of course, one is hopelessly lost fixing power supplies without some
> analog knowledge. Understanding feedback and how each part effects

I would love to see anyone understand an SMPSU without understanding 
analogue electronics...

> the other is the key to fixing these parts. I see so many times that
> some fellow will say, I've replaced all the capacitors and it still doesn't
> work. They ask for help but I often don't know where to start. Should
> I begin with elementary electronics or just use them as a remote VOM and
> oscilloscope.

That depends, IMHO, on who it is, and what they are trying to do. If they 
just need to get the machine up and running again, then ask them to do 
some tests, and tell them what component to change. If they want to learn 
about repairs, then explain what they are doing.

Anyone who askes me how to fix their classic computer gets the latter 
approach. I think it's important that you should understands what you are 
doing. I remember talking to a chap in Germany about repairing a 
(digital, but the principle is the same) fault on an HP9810. I had a 
pretty good idea where the fault was at the start, but I wasn't prepared 
to tell him -- that is to make a guess. I got him to do a number of tests 
(including teacing bits of the CPU microcode) to fidn out where the fault 
really was. He ended up fixing his machine _and_ understanding the processor.

-tony