| David Farber <farberbear.unspam@aol.com>: Aug 26 04:14PM -0700 On 8/24/2022 7:00 PM, Phil Allison wrote: > Lotta resistors about too. > Dead easy to check them for opens. > .... Phil I removed the 8-pin DIP op amp and tested one of the amps as described here: https://www.circuitbread.com/ee-faq/what-are-the-golden-rules-of-op-amps I used the schematic at the very bottom of the page as the test setup. The result of the test was that the non-inverting input voltage (4.5V) did not match the inverting voltage input (0.7V) and according to one of the golden rules of op amps: "In a circuit with negative feedback, the potential difference between the inverting and non-inverting inputs is zero...." That means the op amp is defective. By the way, many of the voltage +/- inputs for the quad and dual op amps when measured in-circuit were amiss. In other words, the non-inverting input voltages were not equal to the inverting voltages but perhaps there was no feedback loop? (too many pc traces for me to keep track of.) In summary, I'm going to replace both chips. I think I checked every semiconductor, resistor and capacitor on the board and I'm fairly confident that my diagnosis is correct. Thanks for your reply. -- David Farber Los Osos, CA |
| Phil Allison <pallison49@gmail.com>: Aug 26 04:52PM -0700 David Farber wrote: ================= > > Dead easy to check them for opens. > > .... Phil > I removed the 8-pin DIP op amp ** What op-amp? FYI the LM2903 is a *comparator* so is the LM2901. https://www.st.com/resource/en/datasheet/lm2903.pdf > and tested one of the amps as described here: ** Irrelevant. > By the way, many of the voltage +/- inputs for the quad and dual op amps > when measured in-circuit were amiss. ** Normal for comparators. Your circuit is * non linear * and uses switching to control the SCR and hence output of the charger. ...... Phil |
| David Farber <farberbear.unspam@aol.com>: Aug 26 08:39PM -0700 On 8/26/2022 4:52 PM, Phil Allison wrote: > ** Normal for comparators. > Your circuit is * non linear * and uses switching to control the SCR and hence output of the charger. > ...... Phil I missed that point. I will reconfigure my test circuit and report back... Thanks for your reply. -- David Farber Los Osos, CA |
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