[Test-Equipment] Adventures in Test Equipment Repairs

[Chris Trask]

    About four weeks ago I had one of my stalwart HP3330B signal generators
go bad.  The frequency was off and it wasn't consistent from one setting to
another.  Early this week I finally got around to taking the covers off and
troubleshooting it.

    This instrument is one of the earliest Fractional-N synthesizers made
commercially available.  It's all discrete TTL logic, and it weighs a ton.
I have a pair of these for making IMD measurements, along with a pair of
HP8656A's for higher frequencies.

    It took a day to determine that the problem was with the main phase
detector board that locks the wideband VCO to the digital synthesizer.  The
first part found to be defective was a custom part (shudder!) that turned
out to be the TTL equivalent of a 74HC157.  Put in a new one with a socket,
and it started to show signs of life, but still not locking up.  Then found
a second defective part, a 7473.  Took that out and put in a socket, but
when I went looking for a device I found that I had none in LSTTL or HCMOS.
None available locally, so I thought I'd call Mouser and get a few.

    But then I remembered an old parts cabinet that I've had for over 25
years.  It's full of carbon composition resistors, RTL logic (I remember
when the Fairchild uL series was new), and early linear ICs (the Fairchild
uA series).  In it was an envelope with about 10 of the 7473's.  I picked
out a nice clean one (National), bent the leads to fit the socket, and
plugged it in.  Put the unit back on the bench and installed the card.
Attached the test equipment leads.  Turned everything on.  Set the frequency
for 1.0000000MHz and bingo!  The frequency counter said I was right on.  Now
I have to go back through the entire alignment procedure so that it tracks
properly.

    Here's the fun part:  I probably bought those parts almost 30 years ago
from a place called Poly Paks.  They were absolutely the best thing that
ever happened to experimenters.

    Never throw old parts away.

Chris

     ,----------------------.       High Performance Mixers and
    /    What's all this     \    Amplifiers for RF Communications
   / extinct stuff, anyhow?  /
   \  _______,--------------'           Chris Trask / N7ZWY
  _ |/                                  Principal Engineer
 oo\                                  Sonoran Radio Research
(__)\       _                             P.O. Box 25240
  \  \    .'  `.                     Tempe, Arizona 85285-5240
   \  \  /      \
    \  '"        \                     IEEE Member #40274515
     .       (  ) \
      '-| )__| :.  \              Email: christrask@earthlink.net
        | |  | | \  '.       http://www.home.earthlink.net/~christrask
       c__; c__;  '-..'>.__

                       Graphics by Loek Frederiks





----- Original Message -----
From: "Tom Dawson" <wb3akd@earthlink.net>
To: <test-equipment@mailman.qth.net>
Sent: Thursday, December 11, 2003 1:28 PM
Subject: [Test-Equipment] hp 3586 gpib commands?


>
>
> My usual plea.......anybody have a list of 3586c commands? (I never get
> manuals with my stuff)...
>
>
> Thanks to all who replied regarding the peeling meters and all..
>
> 73
>
> Tom
>
>
>
> _______________________________________________
> Test-Equipment mailing list
> Test-Equipment@mailman.qth.net
> http://mailman.qth.net/mailman/listinfo/test-equipment