PCB IC repair question

dyno

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Working on a pcb that is not working, I have randy fromm's big blue book and in it he says you can use a 6volt battery and some wires to track down a bad IC by grounding the one wire and connecting the positive lead to a node of one of the IC's and if there is a bad IC it will get hot. Not sure if anyone else has tried this but I am having no luck unless I am doing it wrong(which is a possibility). When the board is powered up there are a few IC's that are getting hot, does that mean they are no good? On a handful of ICs the power reading on the legs are in the mid 1vdc to just over 2vdc which means something aint right. Any ideas to isolate the problem?
 
The first thing is to make sure the board is getting the correct power. Check the voltages at the board connector.

Second, lots of IC's run hot. That is their normal mode of operation. Randomly poking them with 6Vs just sounds like a good way to make sure they are bad. You just fried them. Not all chips run at 5V. You need the data sheets to know which leg to power up and which to ground and these are not always consistant.

I could be wrong, but that just sounds like a bad idea.

ken
 
isn't there a way to measure continuity or voltage across like the first and last legs of an IC to see if it's good or not?

like I have a board where the inputs are stuck closed on a few switches, and I'd like to see which driver IC is bad. or do you just "shotgun" (replace all, right?) them all and see if the problem goes away? :)
 
Working on a pcb that is not working, I have randy fromm's big blue book and in it he says you can use a 6volt battery and some wires to track down a bad IC by grounding the one wire and connecting the positive lead to a node of one of the IC's and if there is a bad IC it will get hot.

Another horrible idea from our dear uncle Randy. :( I would suggest sending it out to someone for repair if you're not 100% sure of how to fix it. What board is it?

EDIT: Check that, it's Avalance isn't it? Yes, some ICs on those old Atari boards do run hot.
 
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Most boards have chips that run hot under normal circumstances. A good example is ram, proms, customs. If a TTL is hot there is probably an issue but that doesnt mean the the issue is with that particular chip, just a result of another problem. Then there are some TTL's that run a little hot so its certainly no sure fire troubleshooting method.
 
isn't there a way to measure continuity or voltage across like the first and last legs of an IC to see if it's good or not?

You can find some blown ICs using the diode test on your meter. Applying a voltage across a chip with a battery is not a good idea... more likely to cause problems than find them.
 
Skip the 6V battery and get a logic probe (one with a tone for logic high and low is best). With a little googling on logic probes and how to read a schematic you will be on your way and we are here to help. Just be fearless and have fun.

Bill
 
Not to mention its pretty damn hard to mess something up using a logic probe...unless your extremely clumsy and short pins out.
Get a probe and spend alot of time poking around on a working board and look at the schematics while your doing it. This will help you understand what your seeing.
 
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