The legs of the chip in question aren't rusty by any chance are they? I've had that cause signal / voltage drop before and just going through and replacing the worst of the rusty chips on the board in question resolved it's issues. Just a thought :) Martin. On Saturday 02 April 2005 16:00, Robert C. Bullock wrote:
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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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. _______________________________________________ Techtoolslist mailing list Techtoolslist@flippers.com http://seven.pairlist.net/mailman/listinfo/techtoolslist
_______________________________________________ Techtoolslist mailing list Techtoolslist@flippers.com http://seven.pairlist.net/mailman/listinfo/techtoolslist
participants (4)
-
Adam Courchesne -
Andy Welburn -
Martin White -
Robert C. Bullock