14 May
2007
14 May
'07
4:50 p.m.
On 5/14/07, Jules Richardson <julesrichardsonuk at yahoo.co.uk> wrote:
I'm guessing that old (circa early-70s) electrolytics which have a
green cap
at one end and a red cap at the other are polarised
and that the green
end is
-ve. Can anyone confirm to save me tracing out
schematics?
They're in the power supply of an IME-86s calculator and are decidedly
past
their best :-) (At least four of the ten in the PSU
are showing signs
of major
leakage)
The rest of the machine *looks* healthy enough; once I've replaced the
electrolytics is there any good reason not to slowly run the system up
on a
variac (rather than giving it full AC from the start)?
Not sure on the capacitors. My IME-86 doesn't have any capacitors like
this -- all of the ones in mine are actually marked + and -.
If you've replaced the capacitors, there's really no need to use the
variac to power it up. Typically, the variac is used to slowly ramp the
power up to allow old capacitors to be observed to make sure none start
leaking or smoking. Other times variacs are used (typically with a
dummy load in place of the actual calculator circuitry) to perform
capacitor reformation.
One thing that using a variac to power up a machine like this is that
power--on initialization circuitry can become quite confused when the
power doesn't come up at the normal rate. This can mean that when the
variac gets up to full voltage, the calculator may "act" dead, and
require pressing "CLEAR" to reset the machine. Sometimes, though, this
doesn't even work as the logic is so locked up that the "CLEAR" key
won't even make it right.
The suggestion of powering up with a smaller fuse in place is a good
idea, though you have to be careful, as if the fuse pops, you're not
really sure if it popped because the rating is too low, or if there's a
fault which caused it to blow.
One thing that I'd recommend before powering it up is to pull all of the
cards (except the core card, which is hard-wired in IIRC), and clean all
of the edge connector fingers. Even light levels of corrosion on the
edge connector fingers can cause enough resistance to throw off the
logic levels and cause the machine to malfunction.
IME's early calculators are quite wonderful machines. The machines have
a particularly interesting legacy in that the Japanese company Nippon
Computing Machine (a.k.a. Busicom) copied the early IME designs to
create their first calculator. NCM/Busicom became famous for developing
the first electronic calculator (in conjunction with Intel) to utilize a
microprocessor (the Intel 8008) rather than a hard-wired or
microprogrammed calculator-specific architecture.
Rick Bensene
The Old Calculator Web Museum
http://oldcalculatormuseum.com