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PC oscilloscopes and real oscilloscopes

Discussion in 'Hobby Electronics' started by Mike, Aug 28, 2004.

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  1. Mike

    Mike Guest

    My 40 year old valve oscilloscope blew the mains fuse. I replaced the fuse but
    now it just makes suspicious something-is-getting-hot-and-might-explode sort of
    crackling noise (as if one of the electrolytic capacitors is getting ready to
    make a quick exit). Given its age it's probably not worth spending the time
    trying to figure out what's wrong.

    I'm looking for a replacement with 2 channels and a 10MHz bandwidth. Looking at
    Dick Smith and Jaycar it looks like $500 for a real scope or $300 for a single
    channel (low resolution) LCD screen scope.

    Does anyone have experience or recommendations for a PC scope, either a plugin
    card or an external box that plugs into the parallel or USB port ?
    Using the sound card isn't an option because of the low sample rate.

  2. John Smyth

    John Smyth Guest

    Did you have a look at what scopes you can get secondhand on ebay?
    John Smyth
  3. Hi Mike,
    Unless you need the digital storage or spectrum analysis capabilities
    of a PC scope, stick with a proper analog scope. You will find analog
    scopes still have the lead in ease of use, responsiveness, bandwidth
    and dynamic range. You need a fairly expensive high end digital scope
    to even start to come close.
    Also avoid the cheap handheld LCD scopes unless you obsolutely need
    the portability, they are just toys.
    Don't buy a new scope from the like of DSE or Jaycar, they are very
    poor value for money. Instead get yourself a second hand or
    reconditioned scope. These can be had on eBay, Oatley or Macservice
    ( For the same price as a new 20MHz
    Jaycar/DSE no-name unit you can get yourself a nice 100MHz+ brand name

    Dave :)
  4. **Find a nice used Tektronix. They go forever and perform beautifully. My
    favourite is the 465B.
  5. What is the make and model is your faulty scope? Just interested to
    know. Maybe it is not as bad as you think. Have you had a look inside?

    John Crighton
  6. Hi Trevor,
    I have been hankering after one of those 465Bs for a a couple of
    decades but I haven't been lucky enough to come across a good
    cheap one for less than $400.
    Just lately I must admit that my opinion of old BWDs has risen and
    that of old Tektronix scopes has dropped slighty. Special Tek ICs
    makes fixing old Tek stuff a lot harder. I have been told that there
    are only a couple of hard to get special bits in the 465B so I am
    still interested in finding one.
    More of a want rather than a need. :)
    John Crighton
  7. **$400.00 is still pretty decent value. After you've used one for awhile,
    you begin to appreciate what quality is all about.
    **I know the feeling. I have three Tek 'scopes (454, 465b and 2430A
    digital), one Philips PM3256 and a BWD 521. The BWD and the Philips require
    regular cleaning of switches and pots. The Teks do not (the 454 and 465 get
    used every day). The BWD has required some power supply rebuilding too.
    Having said all that, the BWD is easy to work on, the Philips is a PITA. The
    Teks don't ever need servicing, apart from calibration (and the odd Nuvistor
    replacement in the 454). Well, except for the 2430A. It requires some work
    and I don't have the balls to attempt it (yet).

    BTW: If you do buy a Tek 'scope, get a Tek probe with it, if you can.
    They're bloody excellent.
  8. I just bought an old 454 recently. It is working but has a few little
    problems that I can live with for the moment.
    When changing the input attenuator switch, the trace shifts up or
    down. The shift control has to be readjusted to bring the trace back
    to the same reference position. A slight pain. :)
    This 454 uses nuvistors also. Where did you find your spare
    nuvistor Trevor, locally or overseas?
    I like the transistor sockets on this 454. Not all the boards have
    transistor sockets, just some, but it is a nice thought for the
    maintenance techs.

    The BWD 820 model is nice to work on. Easy to get at everything.

    I was removing a fan and some associated bits from a junked carcass
    453 for another enthusiast and I was disappointed by the way the
    wiring prevented assemblies from being moved more than slightly.
    I was expecting assemblies to neatly flip out the way on their wiring.
    Nope! They didn't.
    The Rolls Royce quality that I was expecting from that famous
    Tek myth wasn't here, accessibility wise, on this unit.

    The other problem with my 454 is all time base ranges are slightly
    out by the same amount. I can get over this by just moving the
    red knob in the centre of the timebase switch slightly away from
    the "cal" position. There is a pot inside that is supposed to adjust
    the overall time base accuracy but it is not adjusting as expected.
    The displayed waveform lengthens then shrinks as the pot is
    turned in the same direction. The pot doesn't check open circuit
    but I will look into that later. I have a habit of trying to make
    things just a little bit better and then stuffing something. :)
    $100 for a 150MHz CRO, I am happy with it.

    If you are into Tekscopes Trevor or if anyone else is interested,
    I have a couple of boat anchor size valve types that I would like
    to give away to a good home for free. Model 533A and model 549.
    Both not working but there was signs of a trace on both scopes.
    Here is a picture of similar scopes.[email protected]/images/533 scope frmed.jpg
    The ones I have are a bit shabby not nice like the pictures.

    You mentioned Philips scopes Trevor. Maybe you know this
    model from my description. I just can't remember the model
    number. Twenty years ago at one place I was working there
    was a little two tone grey Philips cro with a grey hard plastic
    pouch like container at the back of the CRO for storage
    of the operators manual and probes. Pouch suggests something
    soft , this thin container was hard plastic but I don't know
    what else to call it. The CRO was 15 Mhz bandwidth.
    I have been looking for this model PM??? for use as a battery
    operated CRO. Back then, I modified one of these CROs to
    run off 24 Volts DC.
    The power supply was just transformer, bridge and cap to one
    main regulator, approximately 24V DC input. So it was easy
    to use a couple of small batteries for a few hours running
    where 240V was not available on outside jobs or for using
    it for testing circuits where the CRO could float. Not earthed.
    It was very handy for that.
    I just missed out on buying one years ago for $30 and haven't
    seen another since. I can't recall the model number. Maybe
    you know of it Trevor.

    John Crighton
  9. Mike

    Mike Guest

    It's a Telequipment D43.

    There's no obvious burn marks or bulging caps.
    I'm concerned that something may go bang if I try to find the source of the
    sound while it's switched on. Bits of capacitor flying around the room is
    something I'd rather avoid.

  10. Hello Mike,
    here at the aus.electronics factory the boys are not going
    to let you off with that weak excuse for not fixing your CRO :)

    Cripes! you are more likely to get hurt slipping on a floor at the
    supermarket, getting run off the road by a driver who is drunk,
    dopey on medication, high on drugs or just plain stupid/senile
    or hasn't been to sleep for 24 hours or more. You go out on
    the road and and mingle with dangerous bastards like that and
    now you are backing off from helping a nice little CRO that is
    crying out for your help. Aw c'mon Mike :-(

    Here is a place to down load the circuit diagrams.
    The fourth item down the page is your D43.

    We are all here to help you.

    John Crighton
  11. **I don't think you need be worried about that. Your description sounds very
    much like a buggered power tranny. Expect lots of smoke and a smell which
    will take weeks to dissipate.
  12. Mike

    Mike Guest

    Switched on, after about 20 seconds a thin trail of smoke started
    rising from the mains transformer. As you say, the smell is quite
    distinct and does linger. Makes you wonder what they put into those
    old resin encapsulated transformers.


    (posting via Google as iinet's news server is broken again!)
  13. Hello Mike,
    try disconnecting all the secondary windings and see if the
    transformer still overheats/smokes. There is still a chance
    that you might not have a dud transformer. Try it and see.
    John Crighton
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