Re: [CAD_CAM_EDM_DRO] Re: Hp 7475 Plotter Servo's

On Thursday 20 October 2005 05:29 pm, emc3zach wrote:

> I have not tried changing the chips. I'll have a look at that,
> maybe try and do some logic probe testing on them. I would like to
> know what the problem is. Thanks
>
> Victor A. Estes
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Hugh Prescott"
>
> <hugh345@a...> wrote:
> > Just a thought
> >
> > Have you tried changing the 1489, 1488, 751XX RS-232 interface
> > chips that service the serial port.
> >
> > Could also be the 40 pin UART chip.
> >
> > They might have been damaged by static / misswired cable etc.

Those chips (1488/75188, 1489/75189) are designed such that you can connect
two outputs together and not do any damage. There was one situation where I
kept having consistent problems with those blowing out, and that was a
company that had a terminal connected to a computer in another building and a
wire that wasn't buried very deep -- at an airport! Lots of lightning
strikes not all that far from there. The 40-pin UART isn't connected
directly to the port but is buffered by the other parts, and although they
do fail they fail seldom, and this is something I'd want to use a scope to
find out out, or at least a logic probe.

> > probably common to all HP plotters of that era.

They were pretty common parts to a *lot* of serial equipment over a fairly
long period of time, and I've used bunches of them.

OT: I just snipped literally *hundreds* of lines of stuff from the tail end
of this post, including multiple copies of the yahoo junk and the
list-specific stuff. PLEASE have a little consideration for those of us who
have to download these posts on a dialup line and trim your quoted material
to the minimum necessary to make your point. We will all appreciate it!

--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, a critter that can
be killed but can't be tamed. --Robert A. Heinlein, "The Puppet Masters"