It might be worth noting whether your water is "soft" before applying it to your
boards. The minerals in may municipal water supplies might be sufficient to
cause problems. Getting them off might be a bigger problem than with "normal"
mineral content.
Dick
----- Original Message -----
From: "Pete Turnbull" <pete_at_dunnington.u-net.com>
To: <classiccmp_at_classiccmp.org>
Sent: Saturday, December 15, 2001 1:50 PM
Subject: Re: [PDP8-Lovers] how to clean a PDP8/A, dishwasher?
> On Dec 15, 12:28, Matthew Sell wrote:
>
> > Typically, the time spent "in the water" isn't long enough to damage.
> Even
> > items made of steel and iron won't rust if the water is removed after the
> > cycle is complete. If they sit overnight, well, that's a different story.
> >
> > The only production problem I saw with untreated water was with an
> > electronic test instrument that had a lot of high-impedance signal
> > interconnects throughout. Many signal lines ran for long distances next
> to
> > each other. While the design of this piece of test equipment was
> > questionable, it was our duty to get it to work.
> >
> > The two biggest problems were contaminants from the water supply used in
> > the washing process (city water - switched to using a commercial
> filtration
> > system), and humidity (had to paint a sealant on all of the boards).
>
> That's a well-known problem. Some of the residues from a domestic water
> supply -- especially in hard water areas -- are mildly hygroscopic, and as
> a result, the boards would acquire very small amounts of moisture on the
> surface, especially when exposed to a humid atmosphere. In combination
> with the salts in the residue, this makes for leakage across the board,
> which could easily upset very high impedance circuits.
>
> I heard of someone who had the opposite problem. He designed a CMOS
> circuit which worked fine when forst contructed, but stopped when given
> anti-environment protection or was potted. He'd inadvertantly relied on
> the normal leakage across a PCB to hold the unused inputs of a CMOS gate at
> a particular level. Remove the leakage current and the gate stops working
> properly. Solution: add the pullup resistor that should have been there in
> the first place.
>
> --
> Pete Peter Turnbull
> Network Manager
> University of York
>
>
Received on Sat Dec 15 2001 - 21:35:00 GMT