Dropping Voltages Over Time

Hi gang, I'm a newbie and I just build a set of 4 green pres (great project!). I'm in the testing/troubleshooting phase and I noticed that several voltages on some IC pins vary over time. They drop, slowly. The reference voltage is .07v, and mine ALL register around 4v which drop to 3.99, 3.98, 3.97, etc.

I'm just curious if anyone could point me to what could cause such behavior? I'm assuming there's a problem with my boards since they exhibit this behavior.

The PSU puts out a steady 15v, so the supply voltage into each board is solid.

Any thoughts? I checked zener diodes, the regular diodes, a transistor...could this be caused by a bad cap? Why would all boards behave like this?

I know it's a "general" question but I've bugged the green pre meta folks enough; I'm not savvy enough to figure this out without someone giving me at least a pointer or two in the right direction.

Thanks for any thoughts,

Mike

you can measure the supply voltages to the chip, the output voltage, but that is about it.

pins 2 and 3 on an 8 pin opamp have a really high impedance,

so it is easy to get goofy numbers while measuring them.

the meter is acting like a resistor on those hi-z pins,

which can change a hi-z circuit and maybe make the opamp rail out or something,

That is a very small drop (1/100th of a volt).  How far down do they go and over how much time?  If it is a fairly rapid drop (a minute or two) and then it levels out, I wouldn't worry about it.

Your voltages are in the ballpark, stick some opamps in & go for it!

I would, if I were you........

LOL ok gang I get it! I just thought, a difference of .07v to 4.5v was a LOT! But hey, if the designer says go for it, I WILL!

I will put the opamps in this afternoon and retest voltages with the chips in place and report back - here, and also in the green pre meta for completeness.

Thank-you all! I'm excited about this project!!!! My relay boards for the LED switches all work, and all my LED's light up. Fun stuff!!

Mike

Just a followup...boards stuffed with IC's still had wrong voltages. After replacing zeners, transistors, and caps in the path, the voltages still fall with no IC's but...they are steady after IC's are installed.

So I guess it was a bad cap or two; they were brand new "expensive" ones but I'm going to test them and find out for sure.

Thanks for the help.

Mike

caps might have been in backwards, but they should have blown up by now,

I did check for that! NO blow ups...all electrolytics face the same way in this board (green pre)...still no clue why but...sigh.