Connect with us

Need Help Identifying IC

Discussion in 'Troubleshooting and Repair' started by MBrantley, Jan 28, 2016.

Scroll to continue with content
  1. MBrantley

    MBrantley

    8
    0
    Jan 21, 2015
    Hello everyone,

    I am attempting to identify the ICs shown below. This small circuit was taken off one of our instruments and the two long leads (CURRENT INPUT 1 & CURRENT INPUT 2) are connected to plates from which current is induced by gas phase ions. The outputs (VOLTAGE OUTPUT 1 and VOLTAGE OUTPUT 2) are digitized by an ADC. I am assuming PIN 1 and PIN 2 are Vcc and Ground, however I'm not sure how to determine which one since there are no discernible markings on the IC itself. This board is typically under ultra-high vacuum (roughly 5x10E-10 torr) if they helps in any manner. How would one go about identifying what these ICs are?

    Thank you for your time,

    Unknown_Preamp.png 20160127_203058_resized.jpg 20160127_203133_resized.jpg 20160127_203142_resized.jpg
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,499
    2,839
    Jan 21, 2010
    Well, "what they are" is easy. They're simply op-amps.

    The part number... could be almost anything.

    - pin 2 - inverting input
    - pin 3 - non-inverting input
    - pin 4 - Vcc
    - pin 6 - output
    - pin 7 - gnd

    What value are the resistors?
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,499
    2,839
    Jan 21, 2010
    And what is the supply voltage?

    Oh, and by the way, if you've touched the board other than with gloves, I would recommend you clean it before putting it back.
     
  4. MBrantley

    MBrantley

    8
    0
    Jan 21, 2015
    Hi Steve, thanks for the response. I'm unsure of the supply voltage - the board that was originally driving this is defunct and the manufacturer has gone through two different buyouts. The resistors measured as 5 MOhm.

    This board is identical to the one in the instrument, it's not actually removed from the instrument. However, yes in general we keep our UHV components very clean. :)
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,499
    2,839
    Jan 21, 2010
    Ok, given that the resistors are fairly low resistance (as compared to gigaohms) then you can possibly use a fet input op-amp. You would be looking for one which has low input current and has a valid input voltage range which includes the negative supply rail. Clearly it also needs to be able to drive the output to the negative supply rail as well.

    A reasonable test would be a 9v battery in series with 20M connected to the input (w.r.t. Ground). Measure the output voltage of both your potential replacement and your spare. Differences in output will be due to either resister tolerance or input current.

    similarly, shorting the input to ground via a 20M resistor should produce a similar output (0).
     
    MBrantley likes this.
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-