[rustbucket]

Hi All,

I finished populating a CMOY using the Tangent layout today. When I completed the power stage, I tested it, and it V+ to ground was +4.6v, V- to ground -4.6v. After I finished putting in the amplification stage, I soldered a few resistor leads on to clip alligators to for testing, and... nothing. I starting checking connections for resistance, couldn't find any bad joints or solder bridges.

I discovered that with the OpAmp plugged in, I'm getting 7.5v @ V+ to ground, and -1.6v @ V- to ground. What gives? Take the opamp out of the socket, and all is well again.

Pics will be forthcoming tomorrow if they're needed.

All assistance greatly appreciated!

 

[leftshoe]

What opamp are you using?

When I tried to build a cmoy without using the opamp tangent suggests I had the same problem.

 

[rustbucket]

I'm using the reccomended one from Tangent's web site - It says OPA2132PA on the chip.

Right now I'm not even sure what problems to look for...

 

[The Monkey]

Try to eliminate some of the simplest things first:

- Recheck your soldering. I know you did already, but look one more time, under magnification if possible.

- Clean the board of flux.

- Check your resistor values to make sure you didn't pop in a 10K for a 100K or something to that effect. This is a very common mistake.

- Make sure the opamp is oriented correctly.

Once you post pics, we'll be able to help more.

 

[Pars]

Make sure the electrolytic caps are in with the correct polarity, and are actually connected into the circuit. Hint: with the opamp out, ohm out pins 4 and 8 on the socket to virtual ground. If the caps are not connected, you will see the 4.7K ohm resistance as a steady reading. If they are connected, you will see the cap charging up to infinity (or near... OL on most meters).

 

[rustbucket]

Quote:

Originally Posted by Pars Make sure the electrolytic caps are in with the correct polarity, and are actually connected into the circuit. Hint: with the opamp out, ohm out pins 4 and 8 on the socket to virtual ground. If the caps are not connected, you will see the 4.7K ohm resistance as a steady reading. If they are connected, you will see the cap charging up to infinity (or near... OL on most meters).

The polarity of the caps is definitely good, but I'll definitely check out whether they're acting in the circuit. I'm run the tests mentioned tonight & post pics as well. Thanks for the help!

 

[irchel]

Quote:

Originally Posted by The Monkey Try to eliminate some of the simplest things first: - Recheck your soldering. I know you did already, but look one more time, under magnification if possible. - Clean the board of flux.

why? Shouldn't the circuit be able to run WITH the flux still on it? Cause I've the same problem atm... no sound at all out of my cmoy, although I soldered it pretty well together. But I hadn't much time for tests.

 

[Excalibur]

From what you described there are only 3 things you need to recheck:

Miswired (or short)
Backwards capacitor
or a bad opamp

The easiest thing to do is verify the cap polarity, then throw in any compatible, cheap opamp and see if it works. If not, you'v already narrowed the problem down to one thing...the wiring.

 

[Pars]

Well, actually in addition to just verifying that the caps are in with correct polarity, you also need to make sure they are actually connected into the circuit (had one of those in a troubleshooting thread... they missed a jumpered row by 1). That could also cause the symptom. Beyond that, with the opamp out, just ohm the opamp socket out pin by pin to virtual ground and see what you've got (should match your resistor values other than the power pins... those you should see the caps charging). Then ohm it out adjacent pin to pin (black on one pin, red on the next) and verify you aren't seeing any shorts etc.

Then clean the board