1771 floppy controller questions

From: Tothwolf <tothwolf_at_concentric.net>
Date: Fri Nov 23 03:55:50 2001

On Thu, 22 Nov 2001, Tony Duell wrote:

> > At the time I thought the particular lead might have not been used, and or
> > someone damaged it when installing the chip. I had never seen a chip with
>
> IIRC, the DRAMs in the model 3 are 16K * 1 4116s or similar. All the pins
> are used on these chips. If a pin is missing, then you are going to have
> problems...

I wonder if it would be worth soldering a new pin to what's left of that
chip's lead? It looked like it had just corroded off, but with no other
signs of moisture, I was kinda puzzled.

> > Teflon seems to be very very tough compared to whatever kind of plastic
> > they used in those older cables. What kind of current goes thru these
> > cables? Would it be possible to use one of the more flexible carbon types
> > instead of tin plated copper?
>
> In the Model 3/4 it's just logic level signals. There's a separate power
> connector on the disk controller board. But I suspect that carbon-cable
> would have too high a resistance to be reliable (if nothing else it's
> going to delay the signals somewhat due to the RC time constant of the
> cable and the input capacitance of the chips on the board). Probably not
> a good idea.

Sounds like I may have to experiment a little once I get some clear bench
space ;)

> > Could also use an SIL amp/berg connector and crimp pins to ribbon cable.
> > Might look a little more original, but it would take allot more work to
> > assemble then pressing on an IDC connector.
>
> It's a lot slower to assemble, and it's actually slightly taller. Also,
> those SIL Berg/Amp/Molex connectors are difficult to find in >10 way
> sizes (yes, they're made, but nobody seems to stock them). I prefer to
> use parts I can get in 1-off quantities :-)

I can often find them in large sizes, and use an a sharp X-acto to trim
them to whatever pin count I need. [If anyone decides to try this, be very
very careful, those blades are extremely sharp, and will cut thru the
connector slow at first, then slice thru the remaining material very
fast.] The leftovers can be recycled for even shorter connectors. This
would not be economical for more then a few dozen connectors however.

> > Well, if this is the machine that would not even turn on, that could
> > explain something...I know the factory seals had already been broken. I
>
> Argh!. If the sound board has been plugged into the PSU output there's no
> way of knowing what else has been misconnected and what damage has been
> done. That's one reason to give a machine a complete visual inspection
> before applying power, hoping that if things are totally misconnected
> that the previous owner didn't power the machine up like that (some hope,
> I know).

I think that machine is the model 4, which I think came from a surplus
dealer. There is no way of knowing what all someone tried to do to this
thing before I bought it. The model 3 came from a thrift shop, and seemed
to be in much better overall shape, and may have still had its factory
seals intact.

-Toth
Received on Fri Nov 23 2001 - 03:55:50 GMT