Testing an opamp

[mrosso]

Smoked a J99 opamp. Is there a way to test if a John Hardy 990c opamp is good or blown?

[tele_player]

You'd need to rig up a few resistors and a power supply, or plug it into a known good preamp.

[mrosso]

Can I test it by plugging the 990c in to my A12? Any potential hazzard to worry about like damaging the A12?
thanks

[tele_player]

Maybe Tim will chime in, I won't say if it's safe or not.

[tpryan]

You can get some idea of the condition of the output transistors by measuring the resistance between the output pin and the power supply pins. Measure "in both directions" and compare to a known good part. If the bad one doesn't appear to have wildly different values, post them here.

If you suspect the op-amp to be faulty, I wouldn't recommend plugging it into an A12 without taking some precautions first. Adjust the regulators down to +/-15v and open the output circuit so current can't flow in the OT primary.

[mrosso]

Thanks, Tim.
If I can get squeeze out some free time this weekend, I'll give it a try.
Mario