Ed Price wrote:
"Michael A. Terrell" wrote in message
...
Ed Price wrote:
"John D. Farr" wrote in message
...
It seems that if one owns the equipment, he has a right to the docs
for
it.
John
Would that were true! g
Yeah, in days of old, equipment always came with at least a schematic,
even
if it was glued to the inside of the wood case.
But along the way, stuff got a lot more complicated. In 1960 or so, when
you
bought a Tek 555 scope, you got a full manual too, a couple of inches of
docs. But the pressure builds to trim costs, and by the 70's, you spend
$15k
for an instrument, and all you get is an Operational Manual. The
two-inch
thick Service Manual, with theory, parts list, diagnostic trees, and
typical
waveforms is $100 extra.
If I want the full docs now for say, an HP-8566B or an HP-8471A, I
better
bring a cart. There's an Operator's Manual, a Service Manual, a
Programmers
Manual, and a Parts List, Spares List & Calibration Manual. And they
each
fill a 3" notebook binder!
Actually, the days of big manuals may be gone already. New equipment now
is
much more disposable; you don't find a master tech troubleshooting a
complex
equipment. Instead, they slap on an IEEE-488 diagnostic cable, run the
factory supplied calibration and diagnostic, and, if it can't be fixed
in
software, it likely gets declared too expensive to fix. Junk it!
And if you think that's gonna mean a new golden age of surplus, you're
wrong. Modern gear is more computer than anything else. There's not much
you
can do when you see the signal go into a proprietary chip, and nothing
comes
out. And the construction is now all surface-mount stuff, with trace
spacing
so close it looks like a Moiré pattern. I defy you to probe any ONE
trace.
OK, so maybe you like using a microscope. g
Ed
WB6WSN
Fine pitch surface mount isn't that hard to work on, after a little
training. You do need a steady hand, and the right tools to do good
work. I spent four years doing fine pitch surface mount PC board work,
both testing and repairing boards that make a motherboard for a PC look
simple. Because of my poor vision I had to use a stereo microscope to
see the solder bridges and solder joints that cracked while the board
was cooling in the reflow oven.
--
Michael A. Terrell
Central Florida
Mike:
I'm glad you agree with me, even if I had to read between the lines to find
it!
I'm pretty acquainted with fine-pitch surface-mount assembly. For years, my
company has been doing military command and communications products, all
with multi-layer boards and surface mount and flexible circuitry. We got
dozens of nimble-fingered, tiny ladies working micro-manipulators under
hideously expensive stereo microscopes or even video-cam microscopes.
Robotic assemblers pick & place with a speed that's amazing. We do computer
optical scanning of assembled boards to check for faults. And when a board
doesn't work right, we don't spend much time trying to fix it. If a tech
can't fix it in a few minutes, she harvests a couple of expensive parts and
the rest gets shredded.
And all my experience with a soldering iron and perf boards and wire wrap
simply means nothing in this world. Manual mucking around on equipment like
this scares the hell out of quality guys. They figure that anything you fix
is more than offset by your big, clumsy intrusive actions. Up to the point
where you touch the board, they figure they have most everything under
control about that item's history. You go at that board, poking and
prodding, sticking a needle-point probe who knows where. (Just for fun, if
you have a probe with a 0.01" diameter tip, which is about 7.8 x 10^^-5
square inches, and you push with 3 pounds force, you are exerting some
38,000 psi on the target!) So don't tell me you never broke anything just
trying to find the initial problem.
Let's see, it's not hard to work on. All you need is a stereo microscope and
a reflow oven, and some more "right tools."
So, should the beginner start saving for the oven or the microscope first?
g
Ed
WB6WSN
My favorite SMD tool is a modified Exacto knife carefully shaped on a
sharpening stone to fit between the pins, and the sharp point rounded
off so you don't scratch the fiberglass board. Some of the boards were
16 layer, and cost $8,000 to build and test. They were part of the
L-3com/Microdyne RCB-2000 telemetry receivers.
As far as tools for surface mount work I recommend some type of
magnifier, a good quality adjustable soldering iron. (we used the Ungar
"Loner" series) with a small tip and very fine solder. We used
Ersin/Mulitcore that looked like a hair. A small bottle with RMA flux,
and a hypodermic needle to apply small amounts of extra flux. The
smallest solder wick you can get to clean bad solder off the bad joints,
and use the wet wick method of dipping the braid into the flux and use
it wet so it reduces heat damage to the board. Also, you need to leave
about 1/16" of solder saturated braid when you clip off the used part.
That way you transfer the heat to the joint, not the circuit board.
Like any other repair/rework, it just takes the right preparation, a
steady pair of hands, and common sense.
I am currently out of work, after L-3Com closed the Microdyne plant
and moved it to the rust belt. A doctor at the VA hospital in Gainsville
recently diagnosed me with carpal tunnel in my right wrist and nerve
damage to two fingers of my left hand so its unlikely I will get a lot
of use out of those skills, now. I have been trying to find some
contract board repair, or small assembly jobs I can do from home. The
only electronics work left in the area is Lockheed-Martin, and they have
been shipping jobs to Texas. I have a decent shop, and I have been
working to make it more usable, under the circumstances.
--
Michael A. Terrell
Central Florida
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