apple Lisa2. One working!! - one to go?

Tony Duell ard at p850ug1.demon.co.uk
Wed Dec 15 13:06:20 CST 2010


> 
> Yes, there is always the possibility that his ROM or IWM is also faulty but 
> we'll see what happens.

Indeed. If it works you know where the fault (probably) is, if it 
doesn't, you've not gained any information, but I think it's unliklely 
you'll ahve done any damage...

Can you not try the IWM in your working Lisa, or is it not socketed 
there? I assume the ROM is different between a machine with a 2/10 I/O 
board and an older I/O board + Lisalite, so you can't try that in the 
other machine.

> 
> I actually took the working PSU in question apart last right and replaced 
> all six of the old filter capacitors.  These are the ones I've found tend to 
> blow and smoke eventually.

There's 'preventibe maintenance' and there's 'need;less component 
replacement' :-). 

More seriously, I would always replace suspect components if there's a 
chanve they will do further damage if they fail (e.g. causing a PSU to 
overvoltage.) In the case of an HP120 I repaired a year or so ago, I 
repleaced a dodgy-lookingsmoothing capacitor in the PSU becasue it was 
aimed straight at the CRT. Had it burst, it would probably have broken 
the CRT neck. 

But my experience is that capacitors (at least good qualitiy capacitors) 
are much maligned. Sure I've had to replace some. But it's not as common 
as some people make out. I've got plenty of 30+ year old machiues still 
will all theire original capacitors.

I actually suspect that the capacitors used in modern-ish PCs are going 
to be less reliable now than those used in, say an HP or DEC machine from 
the 1970s.

-tony



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