e/chaos2.pdf
From the other comments it really sounds like bad parts. But, if not, is there any possibility of ESD via the body of SW1? Do any of the "good" units' U2's show increased Vos? And, on the bad units, are the inputs fused/shorted/open, etc?
The answers to those sorts of questions might narrow the possibilities.
1ke/chaos2.pdf m d s .
Hi James, I'm afraid I don't have much good data. Each integrator has a gain of two section in it's other half. And for those I can look at input and output to see if they agree. In two of the cases the output was railed. (I don't recall which rail.. sorry) Opamp was riped out, replaced and no problems. (I'm getting fast at clipping, pulling leads, solder sucking, cleaning and reinstalling... Through hole parts are easy that way.)
For the other two (of four) bad ones I just ripped out U2 and put in a new one, in one case I had to replace the Z opamp also... maybe U2 wasn't blown??? Mostly I've been just trying to get product out the door.
Thanks for everyone's ideas... (I'm still scratching my head.)
George H.
circuit.https://www.dropbox.com/s/afy4kb63ftdo1ke/chaos2.pdf
What's the weather like there? Not to start a weather thread, but are you getting ESD zapped much lately?
Yeah, this can be quite frustrating. My experience with the grey market OP275's was a bunch of boards with 25 op-amps per board. Power was applied, and then you ran your finger down the rows of chips, looking for a hot one. Replace all the hot ones, then maybe one more that didn't get hot but didn't perform correctly, and the board worked. Gave me the willies, but those boards are still running in the field!
You might rig up a pair of resistors to the power supply for the next batch, so you can detect amps that are fully blown without applying full power to the board. Maybe put an LED-resistor across the current limiting resistor, so you get an immediate indication of a shorted op-amp. This would pretty much prove that the amps were blown before you got the board. You are having these made at a contract manufacturer? No telling how good, or bad, their ESD procedures are. If some of the parts are through-hole, it is possible they are getting charged up by handling or maybe test procedures before assembly. Geez, somebody takes 50 V caps out of the box and checks them on a 50 V power supply for leakage, then immediately installs them on the board. That would do it!
Jon
tdo1ke/chaos2.pdf
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No very hot and humid here, (70's), till today... (freeze warning for tonight)
George H.
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mWell there are a bunch of different circuits sharing the same power supply. I might be able to tell if there's a lot of current draw. But maybe not worth it. I'll just test the chaos bit first.
George H.
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ww.highlandtechnology.com jlarkin at highlandtechnology dot com
opam blown b 4 installation ? could it be counterfeit ? how many suppliers you hvae on this part?
so, blame the supplier
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