Logic Probe Advice

vicjw66

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Up to now I have never tried to work on game boards other than test voltages and replace chips that might be the culprit. The game sounds on my spyhunter just went out and I found the voltage to be low (2.5v) on the Ram chip at A6. I don't know if its the chip or something effecting the chip like the Z80 (tests 5.15V)to be the problem. On the schematics it shows all the inputs/outputs of the chips. I would like to buy a logic probe for this and future problems. Whats the consensus on a decent but inexpensive one to buy, and is there a good tutorial on how to use it and interpret the results? Thanks.
 
I was in the same position a few weeks back. I bought a cheap ($7) Eistar probe off Ebay, and it seems to work fine. I've since picked up a very cheap (99 cents) logical test kit from Ebay of the type shown here:

http://www.eandl-global.co.uk/logic.htm

They come up quite often on Ebay too, though they may have different brand names on them. With these kits, you get a probe, a pulser, and a logic clip.

HP Agilent probes also come up often on Ebay, though they usually go for a bit more.

As for how to use them, I'm still learning, buit the PacMan guide at http://lawnmowerman.rotheblog.com/logicprobe.html is a good start. Also get yourself the game schematics and read the logic and electronics chapters of the Atari Book. I'm interested in any other links anybody can suggest.

Dominic
 
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the trick is knowing what the state of the pin you are testing SHOULD be. you could be seeing a "high" state but knowing its supposed to be "high" and not stuck on is the trick.
thats experience. looking at schematics can help but still deciphering is needed. having a second test rig with a known working board can help a bunch. that way you can test a pin on a chip on the working one, know what the "right" state is, and see if you have the same output on the non-working PCB.
 
i also need a logic prob kit found some
do the little cheap pin type work well? liek this one item 170413257776 on ebay if so ill buy one of them

or shoudl i get the kit type?

dont mean to hyjack just was same topic ?
 
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I prefer this type: 400035282608

Has audio outputs which makes troubleshooting easier. You don't have to always stare at the LEDs AND you can use it when troubleshooting audio sections.
 
An oscilloscope is the best way to observe active signals and if they are toggling correctly or look like they should - you can compare the trace on a bad board to a good board. You can also measure voltage with it. Also great for debugging power supplies. They are your eyes in a circuit. You don't need to understand all of the functions of the oscilloscope to use one as a beginner, just basic functions to set beam position, voltage range, and to adjust for a steady signal. You could remove over 2/3 of the controls and it would still be useful for your purposes. I bought my HP 100MHz scope for $25 on craigslist. The clip with all of the leds to show the logic states of all pins is also very handy. I can clip it on the control IC on the board then observe the controlled signals with my scope.

If I could only afford one test instrument, it would be the oscilloscope due to it's versatility. The other would be a multimeter, one that also measures frequency and capacitance and audio for continuity. I bought a talking one that has proven very handy - I can focus on placing the probes on the correct pads and hear the readings.

Logic probes with audio are the way to go - again that audio lets you train your eyes elsewhere.

But nothing beats an oscilloscope..... Like a desoldering station, you'll wonder how you ever managed without it.

Bill
 
Thanks everyone for your input. Scanned over the atari book and it has got some good info. I'll look out for a cheap oscilloscope. My brother the engineer threw his away without asking me if I wanted it. I especially like the idea of an audio feature. Just the other day I was trying to test voltages in my cab and had a heck of a time trying to read the multimeter. I guess I'll start with a logic probe with audio.
 
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