Re: Fixing low TTL signals

I aggree with Andy. If you don't want to replace the IC then just
slap on a pull-up resistor.
-Adam

On Apr 2, 2005 12:52 PM, Andy Welburn <warlords@punkass.com> wrote:
>
>
>
> I have seen another IC piggybacked on top and soldered in place before.. if
> it works, then heh, who cares? J
>
>
>
> The other method I found was to put a 1k resistor to the leg in question,
> then the other end to either +5v or GND, thus pulling the line high or low,
> depending on what you needed. With an oscilloscope, you can often see the
> problem and experiment adding components to help weak gates. When you can
> see the right signals, but their thresholds are just too low, then yu can
> help them along.
>
>
>
> This is a dirty fix method, and some would say that it would die eventually,
> but I disagree, often multiple chips driven off of one signal can get more
> power hungry over time, so rather than replace up to 6 IC's being driven
> from one signal, I tie high or low with a resistor and havn't had any
> problems.
>
>
>
> Sometimes instead of a resistor, I will try a 1pf ceramic capacitor, but I
> usually do this if a signal has too much 'noise' on it, or there's a timing
> issue.
>
>
>
> This doesn't often happen tho, it's a sort of 'tried pretty much everything
> else and I'm shit out of options' scenario. It has got me out of a several
> scrapes in the past, but in general you can find the problem elsewhere and
> fix it properly. But I understand there are certain times when its necessary
> J
>
>
> Andy Welburn
> www.andys-arcade.com
>
>
>
> -----Original Message-----
> From: techtoolslist-bounces@flippers.com
> [mailto:techtoolslist-bounces@flippers.com] On Behalf Of
> Robert C. Bullock
> Sent: 02 April 2005 17:01
> To: techtoolslist@flippers.com
> Subject: [Techtoolslist] Fixing low TTL signals
>
>
>
> I have a Pac with a low 6M* line, when I piggyback a 74LS86 (IIRC, whatever
> chip generates that signal) on it, it's fine, but taking it off, the game
> 'bogs down', sometimes, but plays with no glitches but somtimes the music
> slows down speeds up, etc. Looks like low TTL levels measured at Pin 1 on
> the z80 sync buss card. When I say piggyback, I put my logic comparator on
> it and it raises the levels by about .4V
>
> Do folks just slap some HC chips in the circuit or is there a better
> classic
> way to fix this? Course I could just solder a duplicate chip on top I
> guess.
> I suppose something else tied to that line may be pulling it down but I
> haven't gotten that far yet. Replacing the crappy sync buss single wipe
> socket may help of course.
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Received on Sat Apr 02 16:05:54 2005