Function Generator Help

Discussion in 'General Electronics Chat' started by dude_500, Oct 22, 2009.

  1. dude_500

    Thread Starter New Member

    Oct 22, 2009
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    I just got an old function generator on ebay (Wavetek 143 20MHz). I put the output straight into my scope and it seems to be working, however the output is on the single digit millivolts range. What limited information on it I can find says it has a 30V P-P output. Is there something I'm not doing to get this or is it damaged? Something is rattling inside so I should probably take it apart and check on that.

    Front ports are: VCG IN, TRIG IN, SYNC OUT, FUNCTION OUT,
    Back ports are: GCV OUT, EXT DC OFFSET IN

    Is there something to hook up to these to get more voltage out of it? This is the first function generator I've used so I don't know much about it. No manual for it.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    If the output is in the mV range, something's wrong.

    Can't help you out with your exact manual offhand, but here's a resource:
    http://bama.edebris.com/manuals/wavetek/

    Many oscillators/function generators have similar construction.

    You have to get whatever it is ratelling around inside out first. Do that before you try powering it up again. Then make a full inspection to see if anything is amiss; bulged capacitors, resistors that look burned, vacuum tubes that are burned out (if yours is that old.)

    Primary suspects would be old electrolytic capacitors. Sometimes, even really old electrolytic capacitors can be saved if they haven't started leaking their electrolytic fluids. If you see corrosion around capacitors, they've leaked - and need to be replaced.
     
  4. dude_500

    Thread Starter New Member

    Oct 22, 2009
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    The rattling turned out to be two screws inside that were not in anything. Can't seem to find where they went. I realized that I wasn't turning the attenuator up all the way (the knob was missing so I was just using pliers and not going far enough), but it still only goes to 0.8V P-P. I'll check the calibration knobs inside on the amplifier tomorrow, hopefully that's the problem. The 145 instructions appear to be nearly identical to this model so that should be helpful. I didn't see any obvious internal damage, but I didn't look over it in great detail yet.
     
  5. russ_hensel

    Well-Known Member

    Jan 11, 2009
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    Are you sure about the scope? Try a 9 v battery on the scope (if dc coupled ) Or drop to 60 hz an use the ac scale on a multimeter.
     
  6. dude_500

    Thread Starter New Member

    Oct 22, 2009
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    Yes I use this scope a lot, it is fine. I also just noticed that when I set the scope to DC mode it shows that the offset coming out of the function generator is -13.8V. The offset knob on the generator has no effect on this.

    I found about a dozen capacitors that look like the attached picture. Are these damaged caps or just cheaply made? (note the cracks and holes along the edges)
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    Sorry, but I can only see partial detail in the left photograph.

    The right photo is just black.

    Take more photos on a cloudy-bright day, and re-post.
     
  8. dude_500

    Thread Starter New Member

    Oct 22, 2009
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    Sorry about the bad lighting, here are some better pictures.
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    I've never seen disk capacitors look like that! I can't tell if they split, or were made that way.

    In the left photo, see the 560k Ohm resistor with the dark brown body? That's the old style carbon resistor. Those type will change their value quite a bit over time; usually increasing in value. The newer "dumbbell" shaped carbon film resistors (light tan bodies) are much more stable; they hardly ever change unless they've been overheated.
     
  10. Audioguru

    New Member

    Dec 20, 2007
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    Pointless commentary removed.
     
    Last edited by a moderator: Oct 24, 2009
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