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TECH: Fix for Low TTL levels? HC chips?

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.

Ideas? Does anyone talk fairly serious tech here or should I take all this to sci.electronics.repair?

--
"Quality is the enemy of production."
Homepage - http://members.cox.net/rcbullock/ 'It's lamer than Spaeth's!'
** Replies to rcbullock '"AT"" cox.net ** Sorry, I detest spam.
Reply to
Robert Bullock
Loading thread data ...

whatever

classic

guess.

You've either got a weak chip driving the bus, or something is pulling it down. Try replacing the chip driving first and see where that gets you.

Reply to
James Sweet

No Robert, we are all beneath you and you must take your genius knowledge to a higher level.

Thomas

Reply to
Docrotcod

You cound try an HC, definitely more source/sink current punch, but your switching time may degrade and you'd see some glitching taking place. You may try a 74S86 instead. Still twice more punch than the LS, but with better propagation delays.

Course we don't talk narly well as dem dere sci-ty folk. Us being all out in thu hills I rec-on. ;-)

- Craig

Robert Bullock wrote:

whatever

game

music

1 on

comparator on

classic

guess.

I

wipe

this

Spaeth's!'

Reply to
Craig Yarbrough

According to the schematic, the source of that signal is the 74LS368 chip near the crystal. I've seen that chip fail before. It's not all that difficult to find, so I recommend replacing it.

Then again, the 74LS86 chip that's also connected to that line (as an input) could perhaps be loading down that signal, and may need replacement, instead. But that too is an easy-to-get chip.

Reply to
Matt J. McCullar

Ya know, some folks just take everything as an insult. Hard talk of tech not specific to arcade games is a bit outside the realm of day to day RGVAC, and might be more appropos to sci.* groups. Especially general digital electronics questions.

Let's face it, a the signal tends to degrade around here for many reasons that will be obvious to regular readers.

You too Thomas; if you want to wrongly take what I say as insult, it wouldn't be the first time.

What I should have said was :

"Does anyone talk fairly serious tech here ANYMORE or should I take all this to sci.electronics.repair?"

Spaeth's down to one line responses, and I haven't seen K. Layton, Bob Roberts, Randy Fromm, etc. post in a while.

'Sall I'm sayin'.

And, I'm a sub-genius, just below par in the 130 IQ range. Usually the top couple of percent on standardized tests. 30 on my ACT, 34 in the Science section. Some days I feel smarter than others. For the record. Genius is a strong term. "Needs to apply himself more" would be an accurate statement.

Reply to
Robert Bullock

Ok Rob, no offense meant or taken. I'd tell you to look for the ;-) because it usually indicates a tongue-in-cheek response. But whatever.

If I see posts like yours I usually take the time to help out. It's the least I can do after all the help I've received from the NG over the past few years. If I make a lame attempt to inject some humor, just ignore it and move on.

Cheers!

- Craig

Robert Bullock wrote:

tech not

RGVAC, and

reasons

all this

Bob

the top

Science

is a

statement.

all

Reply to
Craig Yarbrough

I'm just giving you a hard time Robert, no harm intended. That's the bad thing about message boards, it doesn't relay the emotion behind the words.

Thomas

Reply to
Docrotcod

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