12 Jun
2006
12 Jun
'06
12:34 a.m.
Tony Duell wrote:
No, but everything discussed on this list should be :-)
Potting compounds can often be removed without imparing the functionality
Yes. But if you don't *know* what's *inside*, exposing things
doesn't buy you much. The Votrax units are (were) largely
analog devices. So, you need to be able to remove all the
compound without disturbing any of the discretes, their markings
or their *settings* (trimmers, etc.)
Not something you want to casually do on a hard to replace,
expensive little device!
I have never found automatically-produced scheamtisc to be readable. I
prefer to do it by hand, checking each connection. The result is a
diagram I can actually follow...
I want the tool to handle the *connectivity* for me.
I can redraw a schematic without any problem. But,
making sure I've got every foil accounted for is tedious
(if I can have a machine do that for me!). I find it a lot
easier to check a schematic redraw against an *existing*
schematic than against a *board*.
Why> Apart from HDAs, I can't think of any
classic computer device that
Not EVERYTHING is a "classic computer
device" :> can't
be dismantled non-destructively. Mind you, desoldering the HP9100B
I note that
most of Votrax's products are troubling to dismantle
non-destructively (lots of potted "hide me so the user doesn't
know the secrets of my design" stuff). of the device. I rememebr i obtained a thing called a
'Modem Maximiser',
back from the days of 1200 and 2400 baud modems. It connected betweem a
computer and a modem, added a real time clock, parallel port, mailbox,
etc. Quite a fun toy. Anyway, one of the options for this was an
encryption module, that was potted for security. I managed to cut away
the potting compount at least far enough to see the ICs it contained
(8031, 74xx373, OTP EPROM, all SMD packages), work out the
interconnections and dump the EPROM contetns. Worked fine afterwards too.
It is quite messy. Doing field repairs is like a trip to
the dentist (i.e. not fun). And, when you are done, you
have to conformal coat it, again. (else the salt air/water
will eat the lands in no time at all!)
Also, any maritime equipment I designed was
always conformal
coated (several of those being "classic microcomputers" :> )
Confromal coating can be removed without ruining the device, surely? Why? Can't they be taken apart without damage?
It adds a level of stress and risk that I chose not to add.
My goal is to get a nice clean PCB that I can scan and then
convert to a photoplot. From there, I have tools that will
help automate reconstructing a schematic.