Low voltage on IC pins on pcb

dyno

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Working on a pcb and some of the ic's are showing low voltage on some of there pins, I thought I had a bad ic somewhere on the board but I have check them all and they seem fine. Could a bad capacitor, resistor or a transistor be causing low voltage on an ic?
 
Is voltage good on the pcb at or near the edge connector ?
Back track from one of the IC's until you find good voltage.
 
Working on a pcb and some of the ic's are showing low voltage on some of there pins, I thought I had a bad ic somewhere on the board but I have check them all and they seem fine. Could a bad capacitor, resistor or a transistor be causing low voltage on an ic?

Some ic's are supposed to have lower voltage at some of the pins depending on if it's in a high or low state. Not every pin should be at 5v. Are you testing every pin on each IC?
 
The voltage at the edge connector is good, are they ic's suppose to have voltages in the 1v to 1.5v range? I thought the logic low was anyhting below .8v and logic high was anything above 2v and anything inbetween those meant there is a problem.
 
The rise/fall time is too fast for you to measure with a multimeter. You must use an oscilloscope or something equally fast...
 
Just got an oscilloscope a few weeks back and just waiting for the manual for it, the company that sells it is local and had to get the manual from the factory in taiwan because they didn't have it in there files so hopefully by next week I will have the manual. Would a curve tracer help figure it out any easier? Thinking of buying one to use with the scope.
 
The board I am working on is an old Atari Avalanche pcb from the 70's, I have being trying to get it up and running for quite some time. It would have been easier to send it out for repair but I want to learn how to do it myself.
 
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