Faulty OTA?

[bassmeister]

I'm having trouble with several OTAs, I think... Looking at the datasheet of a CA3080, it seems like I should measure ~ 0,7 V at pin 5 (one diode voltage drop)? Correct? I measure 0 V. I measure on different OTAs mounted in a socket on a Tonepad Small stone (IC3).

Is it safe to say that every OTA on which I measure 0 V at pin 5 is broken?

[R.G.]

Not necessarily. The pin could be shorted to ground externally, or could have no drive current to it. Both of those would cause 0V on the pin and the OTA would be good. If you socketed the chips, remove the OTA(s) and measure the voltage on that pin of the socket to verify or eliminate the OTA as the short to ground.

If a wire measures 0V, it can be shorted at either end, or may simply not be driven.

[bassmeister]

Thanks!

I'm right in the middle of trying different OTAs (new ones and presumably broken ones) in different combinations. With just the LFO OTA (new) and one other "broken" socketed, I still measure 0 V. However, when i switch the latter to a new one, I measure ~ 0,7 V at pin 5 (varying slightly). Can I now say that the first one tested is broken?

Does anyone know a good source for a simple test circuit for an OTA?

[R.G.]

However, when i switch the latter to a new one, I measure ~ 0,7 V at pin 5 (varying slightly). Can I now say that the first one tested is broken?

Yep. It's dead.

[gez]

R.I.P...(sniff)

[bassmeister]

All five tested the same way, all dead :cry: I read somewhere on this forum that the CA3080 (perhaps all OTAs?) are very sensitive to currents over 2 mA on pin 5 (instant breakdown). Could be that I shorted pin 5 (they're all interconnected on the Small Stone) to a not current controlled source somehow. Gotta be more careful when probing. This could become an expensive hobby otherwise...