The maximum voltage you can set on 200B is +- 200 mV. In the same time the maximum output is 20 nA. If your resistance is low and the voltage set would require mora than 20 nA the overload led goes on.

I have used this amplifier without any problem. You can use +650 mV or even more.

The most logic reason is that carbon fibre electrodes are broken (low resistance). Check with another potentiostat. Other problem could be a bad selection in the switch a/ b.

Good luck

HI, Ricardo, Thanks a lot. What do you mean for the switch a/b?

Send me a photo of the frontal of the Axopatch with the switches in the position that you are using.

My email is [email protected]

1- You have to work in the whole cell configuration (middle position) ß=1

2- MODE: voltage clamp

3- OUTPUT gain 10x

4- HOLDING COMAND x5 to reach +650 mV (check with an oscilloscope)

5- External command: Off

6- Low pass (start with 1 kHz)

7- All other commands set to O

Another question is where do you connect your ground?

Try and let me know how is going

Good luck!

Thank you, Dr. Borges. One end of my ground is in the bath, and the other side connects to the back of the 200B. This is a regular configuration, but anything wrong?

Are the carbon fibers extended cylinders or beveled disk? Depending on the surface area and quality of the seal between the glass/carbon fiber, you can easily saturate the amplifier.

Thank you, Dr. Hoffman. My electrode is from WPI. It is CFN30-250. 

You should be using smaller electrodes, no more than 7-10 um diameter and either insulated/beveled or no more than 30um extended beyond the glass. Not sure if WPI makes them, other suppliers might.  They aren't too hard to construct with a little patience and a conventional electrode puller, but it takes some practice.

Also a built an electrode grinder is easy. 

I am attaching a couple of papers.

Good luck!

I agree with Ricardo and Alexander. However, we buy our electrodes from Dagan Corporation. They are quite expensive (almost $15/electrode) but they work.