22 May
1999
22 May
'99
9:49 a.m.
> > Once those were clipped and a piece of
anti-static foam inserted beneath
> > the motherboard, the machine now talks to the terminal FAR more reliably
> > than before.
Anti-static foam _is_ slightly conductive, but the
resistance would be
too high to cause problems with TTL (or LS TTL) signals. Had this been
CMOS logic (much higher input impedance, so it's possible to drive the
inputs from high impedance sources), I would have been more worried.
Although I do wonder why you didn't simply cut off the excess leads
yourself...
DOH! =-D Actually, I thought about that. I was going to put some
plastic underneath but it tends to slide around unless you tape it
down. I could put tape underneath but that gets icky after a couple
years. I remembered an Apple II mb a friend had mounted in a PC
case, which didn't fit the mounting screws, so he used some anti-static
foam underneath to support it and it worked fine. I've seen it used
and used it this way all over the place so I guess it never occured to
me that it could cause a problem.
It certainly hasn't. If anything the machine is more stable now.
There's just something about a board full of chips with their leads
an 1/8th inch away from an aluminum ground plane that bothers me.
At any rate, I DID clip the excess leads but since the angles make
it about impossible to see UNDER the motherboard when it's mounted in
the chassis, I decided not to take any chances. Plus the back half
of a N* motherboard is NOT well supported. The center tends to sag
I bit I notice and I also wanted it supported so I wouldn't get
intermittants due to cracks in the aging PCB traces.
Note: BTW, I found a reference in the N* newsletters I have to the A2
16k ram board being susceptible to noise on the bus. The A3 board,
which was available also as an upgrade to the A2, has alot better noise
immunity.
Anthony Clifton