[Coco] [coco] video signal generation

[Gene Heskett]

On Friday 05 January 2007 17:09, RJRTTY at aol.com wrote:
>In a message dated 1/5/07 3:28:57 P.M. Eastern  Standard Time,
>
>gene.heskett at verizon.net writes:
>>>Y ou may want to  consider changing the electrolytic to ceramic if the
>>> value is not to  high.  Albeit somewhat expensive, ceramic caps to
>>> about 10 uF  are available.
>>
>>I've not found them to be terribly dependable  James.  Very low
>> tolerance for any overvoltage.  The Panasonic  dvc-pro's had a few of
>> those here and there, and the failure rates were  about 20% of the
>> teeny little surface mount electrolytics around  them.  So we carried
>> them on the shelf too. Smallish qtys of  course, but then we were
>> buying the electrolytics on 100 count tapes  toward the last of my
>> tenure in that chair.  The electrolytic failures were opens and high
>> esr's, generally non-destructive, the ceramics crowbared, so we
>> noticed the destruction quickly.  Things  get interesting when you
>> have to figure out which trace in a 6 layer  board goes where so you
>> can jumper the burnout.  I gave up and  started replacing the whole
>> board after a while, it was  quicker.
>>
>>I could say do it, but use ones rated at least 2x the supply  voltage. 
>> 6 volters on a 5 volt line don't cut it for the long  haul.
>
>Well I am going to include the input filter since it does work even
>if it is the cap on the GIME's supply line.  I have to build for  the
>worst case situation were the cap is bad and the customer has
>no interest in replacing it.
>
>Also I have personally tried the converter on a half dozen different 
> machines and have gotten feedback from customers and in every case the
> behavior  is the same.   You would think that with random failures at
> least a  few would still have good supply caps on the GIME.
>
>Roy

I agree with the thesis here Roy, but I just looked it up on the 
schematic, and its a .1 ceramic (C8) in parallel with a 100uf x 16 volt 
as C9.  The ceramic is intended to give some decent bypassing in the 
1mhz+ range, and is probably doing a good job yet.  But at 20 years of 
age, there simply is no way there is not at least 5 to 10 ohms worth of 
esr in that 100uf cap.  But, that's what the .1 is there for, so I 
withdraw my concerns about it.

The only other concern is that the average gime and its socket probably 
need, after all these years, an exercising by lifting it 20 thou or so, 
and pressing it back in, several times just to grind through the oxide on 
both the contacts and on the chips little nubs used in place of legs.  
Generally the need for that is pretty obvious though.

-- 
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)
Yahoo.com and AOL/TW attorneys please note, additions to the above
message by Gene Heskett are:
Copyright 2007 by Maurice Eugene Heskett, all rights reserved.