Friden EC-130 calculator schematics?

[Tony Duell]

> I've been looking for schematics for this machine since the early 1990's,
> and
> as yet have come up dry.  They just don't seem to be out there.  My
> understanding
> is that generally, service technicians in the field were trained to repair
> the machines
> on a module basis, e.g., replace this circuit board if it exhibits this
> symptom.

HP had much the same policy. AFAIK there is no HP desktop calculator 
service manual that contains schematics of the logic stuff. If you're 
lucky you get the PSU scheamtics. This includes the 9100, 98x0, 98x5 and 
even the 46/81 machines. For some odd reason, the HP80-series computer 
service manuals did include schematics, but the HP9000 ones didn't. Oh 
well...

The HP serivce manuals (the ones I've seen) are mostly useless _BUT_ I 
still recomend reading them. The reason is occasionally you get some 
information 'in passing' which is very useful if read with a hackish eye

> Service technicians didn't need schematics, because all they really needed
> was
> troubleshooting guide, a knowledge of general operating theory, good test
> equipment,
> and a kit full of every spare assembly needed.  This made it unnecessary for

I am not going to post my rant about board-swapping again. Suffice it to 
say that's not how I reparied any of my HPs. And it's not how I'd repair 
a Friden if I was lucky enough to have one.

> them to repair things down to the component level, except in the case of the
> power
> supply, which may require replacement of individual components.  Everything
> else was modular.  As a result, field techs likely didn't need schematics --
> and
> that was a good thing, because field techs could be 'loose' in their care
> of schematics, allowing copies to be made, leaving them behind, etc., which
> will
> generally not maliciously intended, could result in competitors getting
> their hands
> on the design, which, in those days as it is today, can be a big problem.

Hmmm..... Having done battle -- and won -- with producing repair 
schematics for the HPs, I am not sure this is valid. Certainly for the HP 
machines there's a lot more needed than just a schematic for copying the 
machine (ROM contents, and there were custom chips in some of the later 
machines, for example). And it's not _that_ hard to produce a schematic 
given time. The lack of official schemaitcs might slow down copying 
efforts, but it wouldn't make much difference in the end (it's either 
going to be easily possible with or without the official schematics, or 
very difficult with or without the schematics, depending on the prsense 
of custom parts).

To copy the machine, a simple netlist would be essentially all you need, 
along with a rough PCB layout (assuming you're not just going to copy the 
PCB foils as well). That would be next-to-useless for repair, you need an 
annotated, logically set out schematic.  

-tony