What would cause my logic probe to do this?

dyno

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Working on a board that had some broken traces, fixed one more last night and since then when using my logic probe to check the ics it go from high to low rapidly. It does it on ic legs that are are pulsing, is this a power issue on the board? It doesn't do it on all ics pins that are pulsing just some like on the z80, roms and other associated with that area.
 
It wasn't doing it before. Sorry I didn't state if correctly, the hi/ lo aren't stying solid but flickering hi/lo rapidly back and forth not looking solid. If that makes sense
 
So.....they're more flip-flopping back and forth......fast. This isn't an uncommon state......especially if the boardset you're probing is "watchdogging".

Edward
 
Like ed said, if the board is watchdogging you will see this all across the board on many ic's. Check the watchdog pin on the cpu with your logic probe. On a Z80 it will be pin 26. See if the board has a WD disable.
 
A steady stream of pulses is normal on any data/address line. If it runs for a second then stops, runs, stops...the board is prob'ly stuck in a reset condition. You'll see the reset pin on the CPU toggling hi/low when this happens.
 
No, it's on pulse.Also I can hear like a pulsing noise coming from the speaker when the probe goes from hi to lo.

What was the probe doing before you fixed the traces? Is the pulsing noise coming from the probe, or the speaker of the game?

Some lines pulse high only, low only, or flip between high/low. Check the datasheet of whatever chip you're probing to figure out what you should be seeing.
 
Like ed said, if the board is watchdogging you will see this all across the board on many ic's. Check the watchdog pin on the cpu with your logic probe. On a Z80 it will be pin 26. See if the board has a WD disable.

What is the probe doing on this pin?
 
Watchdog is a term Atari used.......basically meaning the reset circuit. It has kinda become a generic term (like,how some people refer to any soda as a coke).....basically meaning the reset circuit.

Watchdogging basically means your CPU/motherboard is stuck in a loop.......getting lost in it's bootup routine......and starting over.......again.....and again.......again.....etc.

While it is possible to have an issue in the reset circuit/watchdog circuit, this is the least likely place to have issues (speaking from my experience).

Edward
 
Would you say there is a "most likely place" for that issue then, conversely?

My experience, something's gone bonkers on the address bus or the databuss.....RAM, ROM, buffers, mux/decoders, and a slew of other stuff. Not always an easy fix.

Obviously, check the reset circuit first. Like anything else, it can have issues.....and it's generally quick and easy to check out.

Edward
 
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