1771 floppy controller questions

From: Tothwolf <tothwolf_at_concentric.net>
Date: Thu Nov 22 05:12:29 2001

On Thu, 22 Nov 2001, Tony Duell wrote:

> > It's more a matter of room than time right now, as my old "shop" is packed
> > floor to ceiling with computers, parts, and so on. My benches are also
> > currently covered up with even more parts and boxes.
>
> I know exactly what you mean.... :-)

Guess it comes with collecting eh?

> > I seem to remember one of these machines had a chip in one of the ram
> > banks that was missing a pin. It looked like it had corroded off. It was a
> > ceramic package with gold plated leads.
>
> Ah, if you have a visible problem like that, then you'd better fix it
> ;-). The machine is unlikely to work if a chip is missing a pin. Once
> you've fixed that, you can start the real troubleshooting...

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
its lead corroded off like that. There's no visible water/moisture damage
on the rest of the board either, which seemed very odd.

> > replace it with either a similar cable, or an IDC cable, as you suggested.
>
> I've not found a source of the original type of cable. And I don't like
> it much anyway (it seems to have reliability problems, which get a lot
> worse if the cable is inserted and removed a few times).

Have you thought of trying a similar cable made from the newer plastics?
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?

> What I normally do is unsolder the connector from the PCB. Replace it
> with an SIL header (maybe just a row of pins, maybe one of the 'box
> headers used with the IDC sockets with one row of pins removed). Then use
> IDC cable/sockets to link the headers. Make sure you use the same row of
> holes in both sockets, of course. I've done this in several machines and
> not had any problems.

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.

> > My model 1's keyboard cable had the same problem, and I replaced it with a
> > short bit of ribbon cable soldered directly to the boards. I'm planning to
> > replace that again with something better the next time I work on it.
>
> The origianl M1 keyboard cables was a solid-core ribbon cable soldered to
> both PCBs. It breaks if you unfold/reassemble the boards a few times. A
> piece of normal ribbon cable seems to be a suitable replacement.

That's exactly the problem mine suffered from.

> > I think I saw some sort of temperature alarm/sensor plugged into the
> > output of one of the supplies in one of these machines. Was that a 3rd
> > party add-on or something that came standard?
>
> If that's what it is, it's certainly not standard.
>
> But disk-based M4s have a sound board. A small PCB with a 74LS74 chip, a
> transistor and a beeper-thing on it. It has 4 wires coming off it, ending
> in a 4 pin 0.1" Molex socket. It looks as though it could plug into a PSU
> output connector, but it doesn't (doing so will kill the '74 at least).
> It connects to a 4 pin plug on the CPU board just above the keyboard
> connector. If yours was plugged into the PSU when you got the machine
> then the previous owner was terminally clueless, and expect all sorts of
> other problems!

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
wish I could get to these machines right now, I sure want to have another
look and fix em :P

-Toth
Received on Thu Nov 22 2001 - 05:12:29 GMT