Testing chips on PCB

scottsmith

Member

Donor 2012
Joined
Jan 25, 2011
Messages
335
Reaction score
1
Location
Duncan, South Carolina
Read through the sticky writeup on testing PCBs above but have a question...

Do you test ALL chips (e.g. RAM/ROM/EPROM/etc.) using the lower left and upper right pins (to check for good 5V)?

Assuming of course that the notch is in the correct place...

Thanks -

-scott
 
Read through the sticky writeup on testing PCBs above but have a question...

Do you test ALL chips (e.g. RAM/ROM/EPROM/etc.) using the lower left and upper right pins (to check for good 5V)?

Assuming of course that the notch is in the correct place...

Thanks -

-scott

I learned in college that usually when you see ALL it is usually wrong. Most chips are like that but some have little or no dc voltage and others like a z80 have the voltage in about the center of the chip. Most of the 16 pin chips will be like that.

I usually will just probe a few chips for the +5 on the 16 pin chips. First near the edge connector and then further and further away from it, looking for voltage drop.
 
Even some ttl has the voltage coming in on non standard pins. Most will have +5 across from pin 1.
 
Last edited:
If you are not sure where to probe, just probe the 4 corners of a few 16 pin chips after you plant the black lead to ground (of your multi meter).
 
I think you mean across from pin 1 (highest pin #) has +5V.

Oops, yes. And ground is usually on the opposite corner.
I flipped through my ttl book and found one that is non standard. 74LS83 uses pin 5 for +5 and pin 12 for ground. When in doubt pull the datasheet. I love my ttl databook. Its much faster to flip through it then to download datasheets. You can pick them up off ebay for $10-$20.
 
Do you test ALL chips (e.g. RAM/ROM/EPROM/etc.) using the lower left and upper right pins (to check for good 5V)?
There are plenty of chips where this is the case. You can also use a logic probe or multimeter to confirm very general information - e.g. are any pins high/low/toggling. But in my opinion, it is a better habit to just grab the datasheet, confirm the pinout, and do an informed test of the chip instead.

LeChuck
 
I love my ttl databook. Its much faster to flip through it then to download datasheets. You can pick them up off ebay for $10-$20.

+1 on the digital electronics reference bible. I snagged mine, in hardcover, from a used book sale for $1.
 
Thanks to all.

I will get too checking asap. BTW...I am checking for voltage on my Millipede board. I get solid 5v on the test pin, but I am afraid it may be dropping at some point.

thanks again

scott
 
I flipped through my ttl book and found one that is non standard. 74LS83 uses pin 5 for +5 and pin 12 for ground. When in doubt pull the datasheet. I love my ttl databook. Its much faster to flip through it then to download datasheets. You can pick them up off ebay for $10-$20.

I have it as a PDF file and it saves a lot of time when I am just looking for the pinouts.

ken
 
Thanks for the PDF. I really needed one of those.
Agreed, that would be a handy book to have while debugging (I just keep a stash of datasheets). For books that need quick access / flipping, I still prefer hard copies though .. if anyone wants to sell a copy, let me know.

LeChuck
 
I cut and pasted the pinouts from the PDF onto a couple of cheat sheets for the most common chips I use and now I am going back and adding the logic charts and the common output pins for the logic comparator.

ken
 
I cut and pasted the pinouts from the PDF onto a couple of cheat sheets for the most common chips I use and now I am going back and adding the logic charts and the common output pins for the logic comparator.

ken


If you use a compatator there are some ttl you can use the same reference card for. I socket my reference cards and just swap out the reference chip as needed on the ones that can be used for other chips. I prefer to use the standard cards rather than the zif card whenever possible.
 
Back
Top Bottom