Should you correct production mistakes?

Tony Duell ard at p850ug1.demon.co.uk
Thu Aug 26 13:22:59 CDT 2010


> 
> Tony Duell wrote:
> > When you are cleaning up and restoring a piece of classic computer 
> > hardware, would you correct any minor mistakes made in the original 
> > production?
> >
> > .....
> Personally I'd correct it. I've generally tried to restore the few 
> machines I have owned in my "rolling collection" to a working state. Now 

I think it's fairly well-known here that I like my classics to be 
working. I don't want a shelf of ronaments :-). However, AFAIK this 
terminal will work even with the problem (it had been used for some years 
before I got it, I suspect the fault was there from new, there is no 
evidence that this video monitor PCB has ever been swapped. 

> in my case I'm not so competent at the circuit level so for example I've 
> been known to replace the power supply in an Indigo with a modern PC 
> unit but hidden in the original casing. Asthetically you wouldn't know

I bet I'd know :-). I gerneally take machines apart...
 
> and the machine has several more useful years as a result.
> Like you, I think these machines should be shown to work, and ideally 
> used for some purpose. The heat and stress inside a CRT casing is no 
> place for shoddy construction!

This particualr PCB is right hehind the CRT. It's one of the HP 'ET Head' 
units, and inside the casing are 3 PCBs. A large logic board on the 
underside of the unit (accesible by hinging the case up on the stand and 
releasing 4 Nylatch cips) containing some 200 ICs, the monitor PCB mouted 
behind the CRT, and which is got at by removingthe logic board, 
disconencing cablesm ad fiddlign it out downared, avoiding damaging the 
CRT. and the PSU (along with a mains transformer [1]) which fits at the 
very back is is accessed by removing the top cover. So the monitor PCB is 
not trivial to get to. 

[1] Mine is not the Opto 050 version with a built-in thermal printer. 
That has a full SMPSU. The normal one like mine has a mains trasformer 
giving about 24V AC, and then a linear regulator for the -12V line and 
switching regulators for the +5V and +12V outputs.

> 
> On the other hand there's a strong case for not tinkering with "quirks" 
> that made it to production and affect all machines of a given type since 
> they define the character.

I don;t think this fault has 'chracter'. If it was an open connection, or 
intermittant, the most likely there would be nothing on the screeen at all.

On the otehr hand, I suspect that prodsuction erorrs from 'classic HP' 
that have made it into the field are rare, so perhaps it's worth keeping 
as an example of that ;-)

-tony



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