Good board - bottom view
Good board - top view
Bad board - bottom view
Bad board - top view
I am new here and mainly a hobbyist when it comes to electronics. I work more with electricity than electronics.
Sorry about the Spanish comments on the schematic. I did that when I sent it to the original designer of the circuit.
Please I need some answers here.
I have three identical circuit boards all with the same circuit configuration.
Now two work perfectly and one does not.
On the one that does not work, I have replaced 99% of the components and still no joy. See the diagram.
When I test the voltages on pin 2 and 3 of the LM3900 in the circuit, the output changes but is still unstable.
However the ICs on the good boards are stable.
I did not design this circuit, I am only trying to fix the board.
I have replaced the IC more than once and still get the same issue with the output 2. It should be that output 2 is off and so is output 1 until the supply voltage changes either going higher or lower.
Adjusting P1 and P2 does not help in this case.
This is an edited copy of the whole schematic. Some connections are not shown except those pertaining to the op-amp
The voltages shown are for a good board in green and the bad board in red.
Remember the IC is new, and I have tested the bad board with at least 7 new chips and get the same results. To me, something is really wrong with the design. I have checked the bad board all over for shorted connections and found nothing.
If needed, I can post the full diagram. I used Autotrax dex as my editor so I need to export the schematic as a Jpeg etc. It would be nice if pdf files were allowed.