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Tektronix FG507

Discussion in 'Electronic Repair' started by Charles, Nov 8, 2012.

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  1. Charles

    Charles Guest

    I fired it up today and no joy. Took off all the covers/shields and tested
    all the fuses and still no joy. Reseated all the connectors and ICs.

    Finally, after repeated power on/off cycles it started to work.

    Any ideas? I need this generator for an important project but can't rely on
    it now. Any suggestions?

    Thanks!
     
  2. tm

    tm Guest

    Is there a memory backup battery in it? Is it good?
     
  3. hr(bob)

    hr(bob) Guest

    Bad switch contacts, did you check for any voltages after the pwer
    switch?
     
  4. mike

    mike Guest

    Assume the first thing you did was test it in another mainframe?
    Or at least moved it to another socket in the same mainframe?
    I also assume that you have something else in the mainframe so you
    can rule out a bad power switch or corroded fuse holder or any
    other common stuff.

    The FG507 post-dates my tenure with TM500 engineering.
    It's been 35 years and I'm OLD...so much of what I'm about to
    say may be correct...maybe...YMMV.

    The mainframe supplies unregulated DC.
    ~7V intended to be regulated to +5.
    +/- 20ish intended to be regulated to +/-15V or so.
    Because of the wide line voltage specs and cross loading,
    it's difficult to get more than +/-15V regulated under worst
    case conditions.

    There are two floating transformer windings per hole. You can
    get +/-20VDC if you're careful with the rectifier and regulator
    design.

    Each hole has one NPN and one PNP transistor allocated to it.
    These are often used as pass transistors for power supply regulation.
    I believe that all TM500 stuff of this era had linear regulated power
    supplies.

    A common failure is that the mainframe pass transistors come unsoldered
    at the backplane board and become intermittent. Some plugins run them
    hot, so the transistors themselves can become intermittent.

    FG507 schematic doesn't seem to be available, but almost any TM500
    signal generator from that era will have a similar power supply topology.
    The tm503 manual has all the mainframe parts and pinouts.
     
  5. Charles

    Charles Guest

    "mike" wrote in message
    Thanks Mike. I tried it in every position in the mainframe. Also, other
    plug-ins work.

    I never turned it off and it is still working. I will leave it powered on
    until this project is completed and then look for a new function generator.
    Darn, I really liked the FG507.
     
  6. Guest

    "I never turned it off and it is still working. I will leave it powered on
    until this project is completed and then look for a new function generator. "

    You are SO looking at bad capacitors. If it stops working when you are done and you need it again, put it in the oven on keepwarm. Or change the capacitors of course.

    J
     
  7. JW

    JW Guest

    Manuals Plus claims to have a service manual.
    http://www.manualsplus.com/catalog/product_info.php?sku=82316

    You could also try asking on one of the Yahoo Tekscopes group.
     
  8. JW

    JW Guest

  9. tm

    tm Guest

  10. JW

    JW Guest

    I sent an email, and the search now finds it. It's more $ than the
    Qservice manual that tm linked to.
     
  11. mike

    mike Guest

    Spoken like a man with experience.
    How many DEAD FG507's have you fixed by replacing caps?
    Which caps?
    Please share so others can benefit.
     
  12. Guest

    Do I have to actually fix that particular model to have enough experience to know that tings that have trouble starting up usually have bad caps ?

    J
     
  13. mike

    mike Guest

    My pet internet peeve is people who state with certainty and authority,
    things they know nothing about.

    I stopped short of criticism and asked about your credentials.
    It appears that you have none in this area.

    If you looked at a pile of dead LCD monitors, it's likely that a
    many of them would have bad caps.
    If you looked at a pile of dead TM500 stuff from the FG507 era,
    it's likely that ZERO of them died from bad caps.

    As I stated, that model post-dated my tenure in TM500 design,
    but not by much.
    I can almost guarantee you that the FG507 won't stop working
    intermittently because of "bad caps".
    The symptom of bad caps will be hum on the output and FMing.

    Are we having fun yet?
     
  14. Guest

    "Are we having fun yet? "

    Getting there.
    it's likely that ZERO of them died from bad caps. "

    I read the OP. It didn't die. It fails to start. There is a difference. If you think I was recommending a bunch of caps be changed at random you are mistaken. Any digital thing need proper reset and Vcc or Vdd or whatever to run. If it is not there initially it will never run. If there eventually itwill run forever, but only gets one chance to start.

    That's what I read in the OP. Also, being the type of equipment it is, it'snot likely to be a bunch of caps, just one. It is most likely from the description in the OP. I would be looking at whatever feeds the microprocessor(s) and the associated reset circuits, unless they are all internal. That would be my first thing to do, even though it is not a common failure. (of course it is possble the OP already looked into that)

    I have an intenet filter in my brain. When someone writes something I know that it is just one person saying it and they could be worng, as can I. Maybe I should have phrased it differently, maybe others do not have that automatic filter. You save alot of keystrokes by not including all the "maybe","could be" and all that every time. I thought it was a foregone conclusionthat it was just a suggestion.

    I never claimed to have fixed one of those generators with the exact same symptom and it was C XXX or whatever.

    This is not worth an argument really. I will just take note of what you wrote and perhaps phrase things a bit differently in the future.

    J
     
  15. mike

    mike Guest

    It's unlikely that there's anything digital in that FG507...unless you
    want to call
    the trigger comparator digital.
     
  16. Guest

    It's unlikely that there's anything digital in that FG507...unless you want to call the trigger comparator digital.

    I find that a bit hard to believe but surely is possible. Maybe I'll just STFU now lol. And no, even if a comparator is considered digital that's not what I meant. I guess the thing is older than I thought.

    So really, what do you think is wrong with it ?

    J
     
  17. mike

    mike Guest

    late 70's design.

    My first response discussed the likely power supply topology and things
    to look for.
    My money was on the pass transistors coming unsoldered from the backplane.
    He seems to have eliminated that possibility.

    The symptoms were not clear. "No joy" is insufficient specificity to
    provide much help. I made the rash assumption that the power light was off,
    but who knows.
    There are a bunch of mainframe issues. They get bent.
    The fiberglass is abrasive and wears the socket and can lead to
    misalignment of the contacts and intermittent contact.
    The instrument is likely very simple and should be easy to figger out
    with a scope.
     
  18. tm

    tm Guest

    There is no processor in the FG507.

    The main capacitors are in the mainframe. This unit does not use the AC
    voltages from the mainframe.

    One thing to take a look at is the IC sockets. If they are the TI type, it
    would be the first thing to check as it is a known issue.

    You might google for information on that problem.

    Have fun,

    tm
     
  19. Charles

    Charles Guest

    "mike" wrote in message
    late 70's design.

    My first response discussed the likely power supply topology and things
    to look for.
    My money was on the pass transistors coming unsoldered from the backplane.
    He seems to have eliminated that possibility.

    The symptoms were not clear. "No joy" is insufficient specificity to
    provide much help. I made the rash assumption that the power light was off,
    but who knows.
    There are a bunch of mainframe issues. They get bent.
    The fiberglass is abrasive and wears the socket and can lead to
    misalignment of the contacts and intermittent contact.
    The instrument is likely very simple and should be easy to figger out
    with a scope.

    Thanks mike. I always had a power light. The FG is still running (I will
    not turn it off until later) as my project is not over and I don't want to
    risk that it won't start again.

    My guess is that the mainframe is OK as my other plug-ins all work fine.

    The FG is repairable but difficult if there is no extender card available!
     
  20. mike

    mike Guest

    I jumped to the "dead" conclusion.
    You're likely right about the mainframe if you switched holes.
    But don't generalize that to any failure modes. There are hole
    specific functions that can cause problems.

    You still need all the supplies working, so check that.
    What were the exact symptoms of "not working"?
    What was the output voltage? did it vary with offset/amplitude
    settings? Did it vary with the frequency dial setting?
    waveform settings changes?
    See any output glitches when you changed frequency ranges?
    What did the sweep settings do? It's possible for a failed
    sweep to cut off the current to the ramp.
    If there's a sweep output or a trigger output, see if anything
    comes out there.

    It's basically a pair of current sources charging a cap.
    The triangle is the basic waveform function.
    It gets "rounded off" for sine wave. Square comes out
    of the peak comparator. Make the triangle work first.

    It's a two-wide plugin. If it has two connectors out the back,
    your extender problems multiply. Depending on the internal
    connections between boards, you may need extenders there too.

    Assume if you had a service manual, you'd have said so?
    Try to find it.
     
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