LM4250CN

[Randall]

I have an Ovation guitar preamp in that is dead, no output. I have determined that it is getting power and that the pickup is working as it makes some noise on my scope when I tap it with a little sccrewdriver. The thing has six LM4250CN op amps in it, the most likely source of the problem I think. TI labels it a programable op amp. With no schematic I am in the weeds. The only thing I can think to do is shotgun all of them. Problem is, it is listed as obsolete, and I don't have a clue what or how to deal with a progammable op amp.

What to do?

[loudthud]

"Programming" is accomplished with a resistor from pin 8 to the negative rail, pin 4. If you can figure out how much current is going through that resistor (Ohm's Law), the current draw for that opamp is roughly 5 times that current. If you need to replace one of the LM4250s, any modern low power opamp should do, just remove the programming resistor.

[The Dude]

Here's the datasheet for the LM4250CN:

https://www.digchip.com/datasheets/p...4250CN-pdf.php

I'd start by checking output pins and seeing if any are stuck to the rail, which is probably 9V. You may be able to narrow the problem down to a single op amp instead of replacing them all.

[Jon Snell]

Having repaired many older pre amps, leaking electrolytic and other capacitors are a common failure, as is years of sweat/humidity affecting the pcboard itself.
I doubt an IC is faulty but there is always time for a first.

[Randall]

There are no electrolytic caps on this preamp.

[Jon Snell]

Model number?
Here is a general example of a pre amp output stage with organic electrolytics employed. They don't look like standard axial or snap in capacitors.

[g1]

There are no electrolytic caps on this preamp.

There must be some tiny surface mount cans, or chip type tantalums in there.

[Randall]

It's from the 80's, no surface mount. I'm out. I'm trying to be amp amp repair shop, not all things to all people. No schematic, no component designation. Obsolete ICs. Done. Out.

[Jon Snell]

A TL071 ot uA741 will work in those positions. I doubt they are in fact faulty though.
Each to their own. Why not take the easy way out and fit a new preamp from Shadow. (The company that made it for Ovation), at least you will be making something out of the repair and keep another customer happy.

[Helmholtz]

Advantage of the LM4250 is extremely low current draw.