[Coco] Floppy controller - 7416 failure symptoms?

Gene Heskett gene.heskett at gmail.com
Mon Nov 1 00:53:33 EDT 2010

On Monday, November 01, 2010 12:23:25 am Mark Ormond did opine:

> Still trouble shooting floppy problems and was wondering if anyone can
> tell me type symptoms that failing 7416 chips would have in a
> controller? It's a fd500.
> Also on the fd500 note, does anyone know of a way to add the missing
> cart connectors? (Pin 37 actually, I need a13.)
> I was thinking maybe a rear defroster repair kit to make a contact with
> 30g kanar wire painted in and super glued running to the rom?
> Later,
> dabone

I have used several different methods over the years, with the longest 
lasting being a strip of copper foil from a tape it up and solder it PCB 
kit from 25 years ago.  A 3/8" long piece of that, laid where the trace was 
missing, and pressed in place by rolling it heavily, stuck it tightly 
enough that it never came loose.  I did form the end of it so it rolled 
over the edge by about 5 thousandths so the socket connectors couldn't 
catch it and get under it at insertion time.  That board was in and out of 
an old grey ghost many times as I did not have an MPI back in those days.

I think today, that I would see if I could get under a finger pattern that 
was gold flashed with an exacto knife or similar, and roll it back flat & 
super glue it with a very small drop of glue so it only glued the piece.

The most extreme bit of tom foolery along these lines is still in service.  
I sawed the whole gold plated finger pattern off an expired ISA bus pc card 
as its the same finger spacing as the coco's cart socket, then sawed most of 
the fingered nose off the main board in my MPI.  Then I set both pieces on a 
new 14" mill bastard file and filed them both dead flat & square.  2 teeny 
drops of super glue joined the ends of the boards together well enough I 
could apply a drop of solder (3% silver, much stronger than normal solder) 
across the thousandth of an inch gap between the old solder plated MPI PCB, 
and the gold flashed strip from the old ISA buss card.

I had gotten tired of cleaning the MPI at 2 week intervals just to get it 
to work at all.  Whoever invented the phrase "solder plated" should be 
doomed to eternity keeping about 30 of them clean enough to work.  He was, 
and if he still lives, is an idiot.

That was at least 20 years ago, and that MPI is currently in my system 
running in the basement with the monitor turned off right now.  That was the 
complete and total end of the dreaded crash because the coco or the MPI got 

But, I'll be the first to advise that such an operation should only be 
contemplated if there is no other affordable choice AND your hands are 
steadier than mine are today at 76.  I've lived with a hot soldering iron 
in one hand, and a scope probe in the other for 60 years.

Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Don't get mad, get interest.

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