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Failed op amp in my HP 3311A Function Generator — Parallax Forums

Failed op amp in my HP 3311A Function Generator

mojorizingmojorizing Posts: 249
edited 2012-11-27 19:34 in General Discussion
I left my 3311A on last night and found that it wasn't working so well this morning. Looks like U5, the "tuning amplifier", isn't working as it should. The parts manual has it as HP part # 1826-0066 made by Fairchild with their part # as U587777312. Can't find it on the interwebs.

It's a TO-99 8 pin can style op amp. Does it looks familiar to anyone?
op amp.jpg
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Comments

  • Mark_TMark_T Posts: 1,981
    edited 2012-11-26 15:45
    photo of the markings? some of that number is likely the date code.
  • davejamesdavejames Posts: 4,047
    edited 2012-11-26 19:10
    mojorizing wrote: »
    It's a TO-99 8 pin can style op amp. Does it looks familiar to anyone?

    I'm gonna guess it's of the LM101/201/301 family from National:

    http://www.utm.edu/staff/leeb/LM301.pdf
  • YanomaniYanomani Posts: 1,524
    edited 2012-11-26 19:20
    Hi mojorizing

    Studying the original circuit of your instrument, the age of its project, the external capacitor for frequency compensation (if possible with a magnifying glass or pencil microscope, check if its value is 47pF or .47pf as shown in the schematics) and the presence of a symmetry control (offset null) after the current source driver I strongly believe that you can use a LM748QML<=>LM748H/883 from Texas Instruments<=>National Semiconductor. Unfortunately I've found them only at Arrow at >US$ 17 each. Hope you can find a better/cheaper alternative;)

    Yanomani
  • CircuitsoftCircuitsoft Posts: 1,166
    edited 2012-11-26 19:29
    The part number he mentioned is straight out of the service manual.

    Looking at the circuit, you can probably substitute just about any op-amp there. I don't really see anything special with that one.

    LM301 is probably a decent bet. If you can wire an 8-pin-DIP into the board, you'll save a lot of money; 8-DIP LM301 is $0.71 at DigiKey, while the metal can is $8.35.
  • CircuitsoftCircuitsoft Posts: 1,166
    edited 2012-11-26 19:29
    Actually, part number ends in 312. You probably want an LM312, if you can find it.

    http://www.ebay.com/itm/120922013514 Possibly dubious.
  • davejamesdavejames Posts: 4,047
    edited 2012-11-26 19:50
    Circuitsoft wrote: »
    Actually, part number ends in 312. You probably want an LM312, if you can find it.


    An LM312 may functionally work, but the pinout is different.
  • frank freedmanfrank freedman Posts: 1,983
    edited 2012-11-26 22:18
    What is it that makes you suspect the U5 to be the problem? What does not working so well mean? Are all ranges dead, low output, offset by how far etc. Just maybe a few more details so that we all can make (less)educated guesses.......

    mojorizing wrote: »
    I left my 3311A on last night and found that it wasn't working so well this morning. Looks like U5, the "tuning amplifier", isn't working as it should. The parts manual has it as HP part # 1826-0066 made by Fairchild with their part # as U587777312. Can't find it on the interwebs.

    It's a TO-99 8 pin can style op amp. Does it looks familiar to anyone?
  • mojorizingmojorizing Posts: 249
    edited 2012-11-26 22:52
    U5's output on pin 6 has a constant 1volt or so when cycling through the ranges and changing the freq knob. I'm going with either the LM312H or as a second choice the LM301H depending on who carries it when I make my next order for components.

    Today, I've got a Rigol DG1022 function generator coming as an early xmas present. I'll fix the HP and have it for back-up.

    Thanks for the quick replies.... it's nice to see analog experts in this digital forum!
  • mojorizingmojorizing Posts: 249
    edited 2012-11-27 17:17
    Frank, your post got me to look Q9, a PNP 2N5087, downstream of U5. I injected a signal and got nothing, swapped it out with a 2N3906, and everything works. The original Q9 had failed open, unloading U5.

    Thanks again,
    Kevin
  • frank freedmanfrank freedman Posts: 1,983
    edited 2012-11-27 19:20
    Yeah!!!!!!!!
  • davejamesdavejames Posts: 4,047
    edited 2012-11-27 19:34
    mojorizing wrote: »
    Frank, your post got me to look Q9, a PNP 2N5087, downstream of U5. I injected a signal and got nothing, swapped it out with a 2N3906, and everything works. The original Q9 had failed open, unloading U5.

    Thanks again,
    Kevin

    Thank you for the follow up. It's always nice to know "the rest of the story".
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